As I keep going through these updates, some are pretty easy since we’ve learned little since I originally wrote them last year. For cattle, that’s largely because the initial take home message was “they’re not susceptible to SARS-CoV-2, so mooove on.”

That’s not a completely accurate assessment since “susceptible” isn’t really yes/no distinction in many species when it comes to this virus. However, initial studies showed that cattle were so minimally susceptible to SARS-CoV-2 that there was no real concern about health risks to cattle, or about cattle being able to infect other cattle or other species.

The disclaimer I now must add for most of our experimental study results is that we don’t know it this is still true with current variants. Studies in cattle, as with most other experimental studies performed early in the pandemic, used the older / original SARS-CoV-2 strains. As we’ve moved through waves of different variants, particularly alpha to delta to omicron, this virus has changed a lot. For example, omicron is much more transmissible in humans, and behaves differently in multiple other ways too.

Might that impact susceptibility of different animal species?  Maybe. We really don’t know (or at least I don’t).

Experimental studies with a containment level 3 virus like SARS-CoV-2 are a lot of work and expense, are only possible in a small number of facilities, and they require euthanizing experimental animals, so such studies are not common. It would be useful to know if omicron behaves any differently in cattle, but it’s hard to say whether we’ll see any more experimental studies to investigate this.

We can also learn from field studies, such as testing of cattle that have been in contact with infected people. However, there’s often a pronounced aversion to testing in situations like this, in large part due to a desire of some people not to know (because they would then potentially have to deal with the ramifications thereof). Our research group hasn’t tested any cattle, and I haven’t heard of any other field work being done in cattle.

So, we’re left with what we know from experimental studies involving strains of the virus that are basically no longer circulating.  Cattle are probably still minimally susceptible, without relevant human or animal health risks, but it would be nice to be able to say something more specific than “probably”.

Here’s the recap of those experimental studies:

  • One of the first experimental studies in cattle (Ulrich et al. 2020) supported the notion that cattle are pretty resistant to SARS-CoV-2.   The researchers found viral RNA was transiently  detected from nasal swabs of 2/6 cattle that were exposed to the virus, and those two animals mounted a very low antibody response. Viral RNA levels were also pretty low, based on the PCR results, suggesting there wasn’t enough being shed for the animals to be infectious to others, and no cattle that were co-housed with the inoculated cattle became infected. So, in two animals there was some degree of infection that stimulated the immune system to respond, but it was a minimal response.
  • Another study (Falkenberg et al. 2021) infected colostrum-deprived calves (i.e. calves that didn’t get antibodies from their dam and are therefore more susceptible to some infections). After inoculation, the researchers only occasionally found detectable viral RNA by PCR in swabs from the calves, which suggests a very low viral burden. Other tested tissues didn’t show any evidence of infection. Infectious virus was not isolated from any calf, leading the authors to conclude that there was no replication of the virus in the animals.
  • One other study (Bosco-Lauth et al. 2021) tried to infect 3 cattle with SARS-CoV-2. None shed infectious virus. One of the three had a positive PCR result after inoculation. When tissues were tested after euthanasia, live virus was isolated from the trachea of one calf but antibodies against the virus were not detected in any calf. They concluded cattle were “minimally permissive to infection”.

So, going back to our two key questions (and basing our answers on what we know from older SARS-CoV-2 strains):

1) Can cattle get sick from SARS-CoV-2?

  • Probably not. Studies have been limited, but nothing suggests that cattle are high risk of getting infected and sick.

2) Can infected cattle shed SARS-CoV-2, posing a risk to other cattle or other animals (people being part of the “other animals” group)?

  • That doesn’t look like a concern either. Even if the odd cow can get transiently and mildly infected, it’s very unlikely they would be able to pass the virus on to anyone else.

My conclusion in the first version of this review was “…let’s not ignore cattle completely, and still try to keep infected people away from them. But, we can probably relax when it comes to SARS-CoV-2 and this species.”

I’d say that’s probably still a fair assessment, but lack of information about current variants reduces confidence in this statement a bit.

Here’s one that’s pretty easy to update because we don’t know much more than when I posted the original review. That’s partly because it’s not exactly easy to get data on exposure and infection of marine mammals with SARS-CoV-2. I assume no one’s going to do an experimental study on such animals, and we also haven’t been able to get samples when there were potential issues related to captive animals (because some people have a desire not to know, since knowing means you might have to act, and that requires a plan…).

We therefore still know very little about this virus in marine mammals, but there are still some relevant issues to keep on the radar, even though it’s presumably not going to be a major animal health risk in this group, nor a significant human health risk in terms of animal-to-human transmission.

Are any marine mammals actually susceptible to SARS-CoV-2?

We don’t know. As I’ve discussed before, we can look at ACE2 receptors (the structures the virus uses to attach to cells to infect them) for clues regarding potential species susceptibility.  We have to be cautious putting too much faith in predicted susceptibility from this method, and most ACE2 studies have not included marine mammals. However, a couple of studies ranked various marine mammals as having “high” potential susceptibility (Damas el al. 2020, Luan et al. 2020).

A more marine mammal focused modeling study (Mathavarajah et al. 2020, available in pre-print) predicted various whales, dolphins, seals and otters would be highly susceptible to SARS-CoV-2.  Sea lions were lower risk, which might be a very good thing given how they congregate in large populations, often close to human populations. In contrast, they predicted other species, like beluga whales and bottlenose dolphins, may be even more susceptible to the virus than people. High risk species from this study also included a large number of species that are already vulnerable or endangered.

So, if marine mammals are potentially susceptible to SARS-CoV-2, will they actually be exposed?

That’s hard to say. However, this virus has spilled over into many animal species, including wildlife, so we need to think about this careful and consider if there are any ways to mitigate any risks of exposure. As with other species, the greatest risk of exposure of marine mammals is from infected people. There’s the potential for exposure from other infected wildlife if this virus establishes itself more in wild animal populations, but the biggest threat is still humans.

What about direct human-to-marine mammal contact?

This is obviously of concern for a very select group of people, but human-to-marine mammal contact does occur with captive marine mammals and sometimes in field research. Any direct contact poses some risk of passing pathogens (e.g. viruses, bacteria) in either direction. We saw the potential for transmission through the human-to-marine mammal route a few years ago in an MRSA outbreak in dolphins and walruses that we investigated. If we can pass MRSA to marine mammals, we can presumably do the same with SARS-CoV-2. However, in the big picture, infection of captive marine mammals is of limited concern.

How could wild marine mammals get exposed to this virus?

Direct contact between wild marine mammals and people is pretty uncommon, but there are situations where people can have close, or even direct, contact with such animals, such as whale watching enterprises with animals that are habituated to being around people. The other potential concern is exposure to sewage. The SARS-CoV-2 virus doesn’t generally survive well outside of the body, but it will probably survive for a short period of time in sewage. We know that contact with human sewage can result in transmission of other pathogens from people to wild animals. The odds of infectious virus being present in sewage that makes it into the ocean at high enough levels to cause a problem are probably exceptionally low. But, we can’t say it’s zero (especially where there are sewage infrastructure challenges that lead to release of poorly treated or untreated sewage).

Overall, the risk of exposure of marine mammals to SARS-CoV-2 is likely very low, and it’s presumably mainly from the rare situations where people have direct contact with them.

What would the implications be if marine mammals were to be infected with SARS-CoV-2?

Infected marine mammals would likely only spread the virus over short distances and for short periods of time. A small whale pod poses much less risk than a large congregation of sea lions, where there are enough individuals for sustained transmission in the group.

However, since some marine mammal populations are highly threatened, an outbreak localized to an individual pod or small population of certain species could still have significant consequences if infection was associated with disease and their ability to survive. We have no idea about that either.

What about the risk to people from marine mammals?

The risk posed by marine mammals to people is likely negligible. We’re pooping in their habitat more than they’re contaminating ours in any way. Sure, an infected marine mammal would likely pose a risk to a person if there was direct contact, but the odds of that are very low.  Outside of some very population-dense areas, I suspect the potential impact of marine mammal infections on human health would still be very low.

The potential for human-to-animal transmission of SARS-CoV-2 in these animals, no matter how small, can’t be ignored. Places with captive marine mammals should limit contact with them (just like they should be limiting human-to-human contact), and there obviously should be no contact with people who are infected or quarantined because they are high risk.

Similar precautions apply to field research involving marine mammals. This has been a tough situation for any wildlife field researcher, but our goal is to prevent problems, not react to them. We’re still better off limiting contact as much as possible at this stage. When contact with animals is required, we need to maximize protective measures (e.g. masks), minimize contact time, minimize the number of people involved, and do everything possible to make sure infected or otherwise high-risk people don’t participate.

Tourism is another area to address. “Whale watching” should be that: watching from a distance, not trying to get close enough to touch the animal. These animals don’t need any more threats from us – we’re doing a good enough job compromising their survival already without adding in a new infectious disease.

Image from: http://pachicosecotours.com/

This one’s as easy to write as the first version… we still have no clue.

Overall, the health risk to horses from SARS-CoV-2 is probably very low. If horses were getting sick, or at least very sick, we would have noticed by now. I’ve not had any indication that we’re seeing a disease impact in this species. We still don’t know if horses are getting infected from people or whether, if infected, they can spread it back to people, between horses or to other animals. That’s something  we still need to figure out.

Why don’t we have much information about horses compared to other species?

  • Food animals get studied because of concerns about food safety, food security and economics.
  • Pets get studied because of our close contact with them (e.g. they live in our homes and sometimes even sleep in our beds).
  • Wildlife get studied because we’re worried about this virus getting into wild animal populations that could then act as virus reservoirs and sources of new variants.

Horses are a mix of farm animals, companion animals and competition animals. There’s a relatively small pool of researchers who focus on infectious diseases in horses, and there’s limited research support.  Experimental studies in horses are very expensive, because of their size, cost of housing, value of individual animals, and other factors. Field studies are more practical but require people to do the work (we have that) and interest from horse owners and other relevant parties to participate (that’s often missing).

There’s limited interest in (or downright opposition to) surveillance by some, because identifying potential problems leads to having to deal with those problems. If SARS-CoV-2 was identified as a significant issue in horses, that could mean restricting movements on farms with infected horses (which a lot of people want to avoid), as well as dealing with a lot of additional concerns from the general public (including both horse owners and non-horse owners). As a result, we run into barriers to testing in situations where exposure is plausible. I’ve had multiple situations where it would have been very informative to test horses, but where owners/trainers were wary of what would happen if there was a positive result. Since some people are more wary of the impact of a positive result than the impact of the virus itself, we’ve missed out on opportunities to figure out whether there’s any risk to (or from) horses.

So, what do we actually know about SARS-CoV-2 in horses?

One study from Italy tested 34 horses from 2 farms that were exposed to infected people. None of the horses tested positive. The timing of testing isn’t exactly clear, but the study suggests that horses were sampled fairly late after the onset of disease in people, and it’s quite plausible that short, transient infections could have been missed. In some other animal species, individuals tend to only shed the virus for a short period of time, so if sampling is delayed we may not find the virus (but we can still find antibodies after the fact). This was a good initial study to have in horses, but we need more studies where sampling is done closer to the time of onset of disease in people, and ideally with follow-up antibody testing in case we miss the potentially short window when an animal may be shedding the viral bits that can be detected by PCR.

Beyond that, we have older studies that looked at the composition of the ace2 receptor in different animal species. Ace2 is the structure that SARS-CoV-2 uses to attach to the body’s cells. If the virus can’t attach to cells, it can’t infect them. The structure of this receptor varies between species, and that accounts (in part) for differences in species susceptibility. One study ranked the likely susceptibility of horses to SARS-CoV-2 to be equivalent to cats (specifically domestic cats and lions, both of which we know can be infected) and camels (which we also know nothing about, beyond that they are a host for another zoonotic coronavirus that causes Middle Eastern Respiratory Syndrome (MERS-CoV)). We have to take predictive studies like these with a (big) grain of salt, because the real world situation hasn’t always mirrored what was predicted.  These studies tell me that we should pay more attention to horses and see if there’s a problem, not that a problem is likely.

What should we do?

Some surveillance for SARS-CoV-2 in horses would be good. Testing horses that have been exposed to infected people would be interesting and let us know more about the potential interspecies spread of the virus. There have been outbreaks of COVID-19 in grooms in racing stables, a population that’s probably very high risk for infection and for working while sick, and of course they have close contact with their horses, so a situation like that would be a good place to start some equine surveillance.

However, the most important thing we need to do is stay away from any animal, including horses, if we have COVID-19. It’s better to prevent a problem than deal with it, and if we reduce the number of infected people that have contact with horses, we reduce any potential problems.

Mink are not a species most people think about. When they do, they typically think of mink coats or fur farming protests. While the mink industry has been on the decline in most regions for many years, there is still a massive number of mink being farmed for fur internationally. Some of these farms are very large, which makes for lots of animals in close contact with each other, and in contact with their human caretakers, which leads to the risk of pathogens such as SARS-CoV-2 passing back and forth between them all.

Mink aren’t the only critters in the mustelid family that are a concern when it comes to SARS-CoV-2. Any species from the mustelid family probably has similar susceptibility to the virus.  The domestic pet relative of mink is the ferret. Ferrets are “niche” pets but they’re far from rare, and many ferrets have very close contact with their owners.

So, we have widely different issues in how we manage and interact with different mustelids, whether on a farm, in the home or in the wild. Regardless, the net result is situations where there’s a good chance for respiratory virus transmission.

What’s the story with mink and SARS2CoV-2?

There’s been a lot of attention paid to mink during the COVID-19 pandemic, even since the original review I posted last October.  I think it’s fair to say this caught us off guard. No one was talking about mink or risks to/from mink farms at the start of the outbreak, even among those of us who were thinking about risks from other species (lots of people tried to ignore animal risks altogether from what was clearly an animal-origin virus, but that’s a rant for another day).

While we may not have initially paid attention to mink, SARS-CoV-2 did. Mink are highly susceptible to this virus, and there have been widespread outbreaks on mink farms, first identified in the Netherlands but subsequently in multiple countries as well (including Canada and the US).

What happens when SARS-CoV-2 makes its way (from people) onto a mink farm varies, and there are still lots of knowledge gaps. Some affected farms have had few health issues, while others have reported widespread illness and deaths amongst mink, especially older or pregnant mink. The virus seems to have persisted on some farms, at least for a while, with little apparent disease, while on others it seemed to burn through the population and then disappear like a more classic respiratory outbreak. Why? We’re not sure. This virus clearly can cause disease in mink, but it doesn’t always. There may be a predilection for severe disease in mink of a certain age, or in pregnant mink (as with people), but there are still lots of things we don’t understand.

Can mink infect people with SARS-CoV-2?

For most species, I say “we don’t know if they can infect people and it would be hard to figure out”, we know that SARS-CoV-2 can definitely be transmitted from mink back to people, because of the nature of spread and sampling that has been done on mink farms and the people who work on them. If mink and people on a farm all had positive tests, you couldn’t necessarily determine whether some of the people were infected by mink or whether the people all infected each other. However, viral sequencing and the timing of infections on some mink farms has provided more information than we can usually get. Tiny, mainly innocuous changes in the virus commonly occur during replication, and those changes create a kind of “signature” that can help us track the virus better. Using sequencing, you can track how the virus evolves on a farm, where the initial infections are a strain that’s present in people in the community (since that’s where the virus usually comes from), and then the strain changes a bit as it’s transmitted over and over between mink. If that slightly modified strain then pops up in people on the farm, it’s strongly suggestive that the virus was spread from mink back into people.

Are mink farms a reservoir for the SARS-CoV-2 virus?

That’s an important question and a big concern. “Reservoir” can be considered a few different ways. The main concern is whether the virus can spread on a farm for prolonged periods of time, creating an ongoing source of exposure to people (and possibly wildlife) on the farm, including new variants of the virus.

Can the virus spread from mink farms to the community?

  • Yes. That’s been shown. It’s rare in the grand scheme of human COVID-19, but it has happened.

Can the virus spread from farmed mink to wildlife or other animals?

  • When SARS-CoV-2 is present on a farm, there could be exposure of a range of wildlife that may come and go from the property through contact with mink feces (which fall through the animals’ cages and accumulate under them) or from aerosol exposure (e.g. virus in dust particles within the animal sheds). There’s also the potential for exposure of farm animals (farm dogs, barn cats). Transmission to farm dogs and cats has been identified.
  • Infected “feral” mink were found around an infected farm in the US; these were presumably mink that had escaped at some point from a nearby farm, but it shows another way the virus can make its way off the farm.  This has also been seen in Spain, where infected feral American mink were found (and at some distance from the closest mink farm…). Since American mink are not native to Europe, it’s safe to say those mink (or their ancestors) were escapees at some point. Where the virus could go from there is a good question. It might just burn out in the wildlife population (since wild mink are primarily solitary creatures), but if it’s able to continue to find susceptible hosts (e.g. wild mink, certain mouse species, white tailed deer), it’s possible mink farms could be a source of broader spread, bridging human SARS-CoV-2 with wildlife.

Can the SARS-CoV-2 virus be sustained on a mink farm long term?

  • A big factor that might influence the risk from mink farms is whether there is long term, sustained transmission of the virus within the farmed animal population. If the virus enters a farm, burns through the population quickly, and is eliminated (either naturally or through culling of infected animals), then there’s lots of transmission but over a very short period of time. If SARS-CoV-2 enters a farm and continues to spread over months (or even) years by continuing to find new susceptible mink in the population to infect (or re-infect), the risk probably increases substantially. We don’t know how much of a risk it is, but we know there’s some risk because the virus already seems to have maintained itself on certain farms for a long period of time (months). We still have limited information about the long term outcomes, because many infected farms were depopulated, and on those that weren’t long term testing wasn’t necessarily done (or reported).

Are mink a source of new variants of SARS-CoV-2?

In the first 3 parts of this review update that I posted last month, I dismissed the potential for dogs, cats and pigs to be significant sources of new SARS-CoV-2 variants because of reasons like poor susceptibility (pigs), minimal virus shedding (pigs, dogs) or lack of enough animals in close contact for sustained transmission within the animal population (dogs, cats).

Unfortunately, mink create the perfect storm for new variant emergence. They are a highly susceptible species that can effectively transmit the virus mink-to-mink and mink-to-human, and they are raised in large enough groups that there can be widespread and sustained transmission. Since variants emerge due to random mutations, and the likelihood of that is dependent on lots of virus replication, and more transmission leads to more replication, variant emergence is definitely a concern on large mink farms.

“Mink strains” of SARS-CoV-2 have been identified. Whether that’s because the virus adapted to be better able to infect mink or the changes were purely random (i.e. conferring no specific advantage to the new strain in terms of infecting more mink) isn’t clear. However, the new strains provide a way to help track virus transmission in some situations. In early outbreaks, there was concern about a mink variant that was identified in the Netherlands. There was also concern that mink strains with a common mutation (Y453F) that spread from mink farms into the general human population in Denmark might be less responsive to antibody-based treatments used in people  (these are important therapies for high-risk people with early infection). However, there was no evidence that these mink strains would compromise vaccine efficacy, and fortunately they didn’t end up being a significant problem as they weren’t any worse than “regular” strains in people in terms of disease. In fact, there’s some (albeit pretty weak) evidence that mink-derived variants might be less virulent in people. I think we have to assume both things could happen: mink could be the source of new variants of concern that pose more risk to people, as well as new variants that would pose less risk to people. We can’t really predict what will happen, or when.

Realistically, the biggest risk of variant emergence still lies in the human population, since we still have rampant human-to-human transmission of SARS-CoV-2 internationally. But mink are a potential source, and all it takes is one event with the right (or wrong) mutation to cause a problem. Further, as we (eventually) control this virus in the human population, animal reservoirs will become more important, as the relative risk from them will increase if true reservoirs are being created through infection of different wild and domestic animal populations.

How about ferrets? Are they as susceptible as mink to SARS-CoV-2?

Whether ferrets are “as susceptible” to the virus is hard to say, since they haven’t been directly compared. However, ferrets are clearly susceptible and are able to effectively transmit the virus to other ferrets. We’ve seen this in multiple experimental studies where ferrets were infected, got sick and were able to transmit the virus ferret-to-ferret.

I was a bit surprised that we didn’t see reports of naturally infected pet ferrets early in the pandemic. That was likely because of limited numbers of ferrets and limited testing. In our surveillance, we only got to test a handful of ferrets.  Despite the small number of reports, there have been documented infections in pet ferrets (e.g. Giner et al. 2021, Gortazar et al. 2021, Racnik et al. 2021) As with dogs and cats, infection in ferrets is likely under-diagnosed, and may actually be a common event that occurs under the radar in households where people have COVID-19. I assume the odds are 50:50 or greater than a ferret from a household with active COVID-19 in a person is, was or will become infected, if it has close and/or regular contact with infected people.

The health impact of SARS-CoV-2 infection on pet ferrets hasn’t been well described. Some get sick, but it’s mainly been mild disease, which fits with the findings of experimental studies as well. Some report infections with limited or no obvious signs of disease (e.g. Shi et al. 2020,  Schlottau et al. 2020Kim et al. 2020). However, more serious disease, sometimes requiring euthanasia, has been reported. That might be related to the dose of virus, as high doses were used in the experimental study where more serious disease was encountered. The overall health risk to pet ferrets is probably low, but we can’t rule out the potential for severe disease, particularly in older or pregnant ferrets, or ferrets with pre-existing health problems.

Can ferrets infect people with SARS-CoV-2?

We don’t know, but they probably could. Since ferrets are susceptible and can infect other ferrets, and we know that mink can infect people, it makes sense that ferrets could also infect people. However, the true risk to ferret owners needs to be considered.  Being able to infect a person is one thing. Actually being an important source of infection is another. To pose a risk, ferrets have to first be exposed to a person with SARS-CoV-2 infection. This would almost always be their owner. In that situation, the owner poses greater risk to other people in the household than the ferret does. The main risk to others is if the ferret leaves the household (e.g. if it needs to be taken to a veterinary clinic for an exam) during the period when the household members are infected.

What are the recommendations when it comes to mink, ferrets and SARS-CoV-2?

Anyone with COVID-19 should absolutely not go anywhere near a mink farm. Period.  That’s the big one. If we’re going to continue to farm mink for fur, there needs to be a strong focus on biosecurity and surveillance for this virus. Surveillance is an issue because of cost (i.e. who pays?) and the general lack of desire among many parties involved to really know what’s going on (especially if the mink don’t look sick).

In terms of ferrets, the same general approach that we recommend for dogs and cats applies:

  • If you have COVID-19, try to limit or avoid contact with your ferret.
  • If your ferret has been exposed to someone with COVID-19, keep it away from other people and animals.
  • If your ferret has been exposed to someone with COVID-19 and is sick, let your veterinarian know, to help determine whether it might be infected with SARS-CoV-2 (do that by phone, at least initially, rather than showing up to the veterinary clinic directly with your ferret).

Next up for a review update… horses.

What we know about SARS-CoV-2 in pigs hasn’t changed a lot since the first version of this post. It’s still a fairly “good news” situation, but one that could also use some more investigation.

Are pigs susceptible to SARS-CoV-2?

Kind of, but not really.  There are somewhat conflicting experimental data, but the debate is really whether pigs have very little vs no susceptibility to the virus. There is obviously a difference between “no” and “yes, but only a little,” but from a big picture standpoint, we don’t currently have evidence that there are issues for pig health, pigs as a source of infection in people, or pigs as a potential reservoir for emergence of new virus variants.

Why did we talk a lot about pigs initially?

At the start of the pandemic, we were worried about the potential for this virus to infect pigs because of their susceptibility to the original SARS virus, and because it was predicted that they would be quite susceptible based on their ACE2 receptor. ACE2 is the receptor that the virus uses to enter the cells of the host. If the virus can’t enter cells, it can’t infect them. Different animals have slightly different ACE2 receptors on their cells, and the pig ACE2 receptor is quite similar to the human ACE2 receptor, suggesting there could be similar susceptibility in both species. Looking at ACE2 receptors has been interesting, but we’ve seen that it doesn’t always link up with what actually happens, as was the case in pigs.

Trying to grow the virus in cell lines from an animal species can provide some additional information about potential susceptibility. In one study, the SARS-CoV-2 virus was grown in 2/3 pig cell types, but did not damage those cells. In another study, the virus grew in the pig cells and caused some cell damage. Similar results were reported in another cell line study.

These all contributed to the concerns about the susceptibility of pigs; however, there are limitations to what in vitro studies can tell us. To get the real story, we need to look at actual pigs. So far, all the information we have about the virus is live pigs is from a couple of experimental studies.

So, are pigs susceptible to SARS-CoV-2?

In one study,  5 pigs were experimentally infected and mixed with 3 other pigs. In another study, 9 pigs were infected and then mixed with 3 other pigs. A third study infected 9 pigs and added 6 uninfected pigs.

  • Nothing remarkable happened in any of these studies. None of the pigs got sick, and all samples collected were negative for the virus. Antibodies against the virus weren’t found in any of the pigs. This all indicated that the pigs were not infected, and there was a big sigh of relief as it appeared that concerns about pigs were unnecessary.

In yet another study, pigs were exposed to the virus via the nose, the trachea and by injection. All the pigs stayed healthy and the virus wasn’t detected in any samples from the pigs, but antibodies against the virus were found in pigs that were injected with the virus. That shows the body responded to the virus, but since it was injected, it’s not really relevant to the natural situation.

However, leave it to Canadians to be disruptive – another experimental study in pigs changed the story a little bit.  It didn’t raise major concerns, but it suggested things are not quite as clear cut as we’d hoped.

  • In the Canadian study, 16 pigs were exposed to a higher dose of the virus, and nothing remarkable happened. Some developed mild discharge from the eyes for a few days. One had a slight cough and was mildly depressed for a few days.
  • Low levels of virus were detected by PCR in respiratory samples from two of the sixteen pigs, but live virus could not be isolated.
  • The virus was isolated from a lymph node of one pig, and antibodies were detected in the blood of two pigs, supporting some level of true infection.
  • Two pigs were added to the exposed pigs 10 days after inoculation, and they didn’t become infected.
  • So, this study showed some degree of susceptibility in pigs, but with infrequent mild disease and no evidence that pigs are infected to the degree that they would be able to pass on the virus to another animal (or person).

Another similar study involving inoculation of pigs with SARS-CoV-2 by different routes (blood, trachea, nose) also found none of the pigs got sick. Viral RNA was detected from oral, nasal or rectal swabs by PCR in some inoculated pigs, but virus wasn’t isolated and transmission to in-contact pigs wasn’t observed. These two studies are still consistent with a “don’t worry” narrative – if there was human-to-pig transmission of SARS-CoV-2, the pig would not likely get sick and would not likely be able infect other pigs or people.

Have any pigs outside of a lab been infected with SARS-CoV-2?

There are no reports of any naturally infected pigs, but I’m also not aware of any actual testing of pigs on farms. (“We don’t think there’s anything to investigate” is often stated with an unspoken “we don’t really want to know.”)

Field data are always useful because experimental studies don’t tell the full story. So, some data about pigs exposed to infected farmers would be useful to have, to round out the story. There have to have been large numbers of pigs exposed to infected people, especially on some large farms in areas where COVID-19 has run rampant. The fact that we haven’t heard rumblings of problems is good. However, without formal surveillance, it only tells us we don’t have evidence of a significant pig health issue. We can’t rule out the potential that pigs get infected but don’t get sick. That’s why we really should have more active surveillance, looking at pigs that have potentially been exposed.

What’s the recommendation when it comes to SARS-CoV-2 and pigs?

The same as for other animal species. If we keep infected people away from animals, we don’t need to worry about human-to-animal transmission, or any subsequent animal health or animal-to-human transmission issues. While the odds of someone infecting a pig are very low, it’s best to avoid exposing pigs to infected people whenever possible. That may not be an option on small farms run by one person or a family, but the more we can keep infected people away from animals (of all kinds), the better.

What about new variants of SARS-CoV-2 in pigs?

That’s the wild card for all our animal discussions. Experimental studies were done early in the pandemic and used the original strain of the virus. The SARS-CoV-2 strains we’re seeing now are quite different, at least in humans. Odds are low that delta or other variants would be much more able to infect pigs, but we simply don’t know. As we see new variants, we need to realize that what we know from earlier work isn’t necessarily still the case. It’s another reason ongoing surveillance would be good, but I won’t hold my breath on that.

There’s not as much to update about SARS-CoV-2 in dogs as there was in cats. We have more numbers than we did before, but the overall issues in dogs and our understanding of them haven’t really changed.

Spoiler alert: dogs and owners can both relax, as the risks are very limited.

Are dogs susceptible to the SARS-CoV-2 virus?

Yes, but… not very… maybe.  It depends on what you mean by “susceptible.”

Nice and clear, eh?

There’s a difference between getting infected and getting sick. Yes, dogs can clearly be infected. However, they don’t seem to be as susceptible as cats, and it’s debatable whether they get sick from the infection… I’m still a bit on the fence about that (more below).

How often do dogs get infected?

This is where we’ve gotten the most information recently.  Studies that have looked at dogs living with COVID-19-infected people have generally identified impressive rates of human-to-dog transmission. In these studies, researchers either look for evidence of the virus itself in the dogs (usually using a PCR test) or they look for antibodies against the virus in dogs’ blood. The problem with PCR testing is that there’s a very narrow window of virus shedding in this species, so it’s easy to miss the window (in which case the test comes back negative even though the dog was infected) based on sampling logistics and timing. With good antibody tests, we can get a good idea of whether dogs were infected in the past (although there are potential issues there too) because the antibodies hang around for a lot longer.

Early in the pandemic, the virus was identified by PCR in dogs from infected households, setting the scene for further studies. The best initial effort was from Hong Kong, where they identified the SARS-CoV-2 virus in nasal, oral and rectal swabs from 2/15 dogs that were quarantined because their owner was infected. Neither dog had signs of infection, both developed antibodies to the virus, and gene sequencing showed that the viruses in the dogs were the same as the viruses in their respective owners. Subsequent work has found similarly, fairly low rates of PCR-positivity among dogs with household exposure to infected people (e.g. Hamer 2021).

Serological studies looking for antibodies against SARS-CoV-2 in dogs have shown that transmission is actually much more common than this, with rates of up to 46% in dogs from infected households (e.g. Stevanovic 2021Hamer 2021). The results from our (hopefully soon to be submitted) Canadian study were similar, with about 43% of dogs with household exposure testing positive for antibodies to the virus.

Some studies have tested blood from undefined populations of dogs, for example by testing leftover samples of blood submitted by veterinarians to diagnostic labs. These studies tell us very little, because there’s no accompanying info about the dogs, particularly whether dogs were exposed to anyone with COVID-19. Not surprisingly, low rates of antibody detection (0.2-3.4%) have been found in these stuies (e.g. Ito et al. 2021,  Patterson 2020, Smith 2021). Whether these positives represent infected dogs from households with infected people vs false positive results isn’t clear.

Do dogs get sick when they are infected?

That’s still unclear. In small experimental studies, dogs could be infected but didn’t show any signs of disease (e.g. Shi et al. 2020, Bosco-Lauth et al. 2020). Field studies are harder to evaluate because there’s nothing specific about the clinical signs we’d expect to see from SARS-CoV-2 infection in a dog (e.g. lethargy, coughing, sneezing, decreased appetite and other flu-like signs). These non-specific signs can be caused by lots of diseases in dogs, so if we find a dog that has evidence of previous SARS-CoV-2infection (i.e. antibodies) and it was reported to have been sick, it’s hard to say whether it was sick because of SARS-CoV-2 or whether it was sick because of something else and had an incidental SARS-CoV-2 infection. Larger and better designed studies are needed to figure that out.

In our preliminary work, we found an association between antibodies in dogs and the owner reporting that the dog was acting sick around the same time the owner was infected. That is to say, this finding was significantly more common in dogs that had antibodies than in those that didn’t, suggesting infection with SARS-CoV-2 could have caused (or contributed)  to illness in (at least some of) the dogs. However, the signs that were reported were very mild and often vague (e.g. “the dog was a little quieter”), so while it might suggest that dogs can get sick, it would seem any illness is generally really mild.

Serious disease from SARS-CoV-2 has been identified in cats, and there has been some chatter about a very small number of dogs getting really sick or dying. However, when you consider the massive number of people that have been infected and the apparent high rate of transmission to dogs, if there was a true serious disease issue, I think we’d see more evidence of it by now. Also, we’re going to find incidental infection in some dogs with serious diseases or that die for other reasons, just because of the large number of infected dogs.

My take-home message on this at this point – with the variants that are currently circulating – is that SARS-CoV-2 poses very little health risk to dogs. More work on that is underway, though.

Can dogs infect other animals or people with SARS-CoV-2?

Probably not. Dogs are probably much lower risk than cats, and the even the risk from cats is still unclear. The fact that the virus has been isolated from dogs (e.g. Hamer 2021) is a concern, because if there was live virus in the dog’s nose, you have to assume there was some risk of exposure to individuals in-contact with that dog. Whether there was enough virus being shed to actually infect someone is completely unknown, and it’s probably exceptionally rare for a dog to be shedding enough virus to pose a risk. Experimentally, dog-to-dog transmission has not been seen. That’s not a guarantee that it can’t happen, since these experimental studies were conducted in an artificial environment with very small numbers of animals, but it provides more support of limited risk.

Overall, I’d say the risk of SARS-CoV-2 infection from dogs is very low. I don’t think we can say it’s zero (we can’t guarantee much with this virus), but I think it’s very unlikely that a dog would pose a realistic risk to a person or another animal.

That said, why chance it? If a dog is infected or at risk of being infected (e.g. living in a household with an infected person), it should be kept away from other people and dogs. Dogs interact nose-to-nose and nose-to-bum a lot, and have a lot of contact with their faces, so keeping exposed dogs under control and away from others is a reasonable precaution. We’ve also seen transmission of other respiratory viruses between neighbouring dogs through fence-line contact, so this should be avoided as well, just in case.

Could dogs be an important reservoir of the SARS-CoV-2 virus once it’s controlled in people?

No, dogs are not susceptible enough to the virus to serve as a reservoir. To be a reservoir, the virus would have to be able to keep spreading dog-to-dog. That’s not going to happen because of the low susceptibility and short shedding time in this species. You’d need a very large number of dogs in regular close contact to even begin to have a risk, and then only IF dogs were able to effectively transmit the virus.

What about variants of concern (VOCs) in dogs?

Variants of SARS-CoV-2 such as alpha have been reported in dogs (e.g. Barroso-Arevalo 2021 and Hamer 2021). That’s expected as different variants become dominant in people, because people are the source of infection in dogs. Unless a human variant has more or less affinity for dogs than the original strains (possible, but not very likely), we expect the strains infecting dogs to be a reflection of the strains infecting in humans. I assume that large numbers of dogs have been infected with the delta variant as it now dominates in people as well.

Could new variants of concern emerge in dogs?

Almost certainly not. Variants develop by chance during viral replication. The more transmission, the more replication, the greater the risk of a variant emerging through random mutation. Since dogs are not going to be involved in sustained transmission of the virus, there’s pretty much no chance we’d see a new variant emerge in dogs and spread back to people. Yes, it just takes one replication error and transmission event for a variant to emerge, but the odds of it happening from a human-to-dog transmission AND the dog then infecting a person are pretty much zero.

Could dogs be a bridge to infecting wildlife with SARS-CoV-2?

Probably not, or at least much less likely than cats. Their low susceptibility, short period of infection, limited (if any) infectivity to others, and limited direct contact with susceptible wildlife mean the odds of dogs being infected by their owners and then infecting wildlife are very low.

So, we shouldn’t worry about SARS-CoV-2 in dogs?

Worry, no.  But we still need to pay attention to it.

What should be done with dogs?

Do the same as for cats:

  • If you are infected, try to stay away from animals… all animals, human and otherwise.
  • If your dog has been exposed to a person with COVID-19, keep it inside and away from others.

The risks to and from dogs are exceptionally low, but precautions are common sense and easy… a few short term mild hassles for some peace of mind.

Ultimately, dogs are part of the family – so if your family is isolating, the dog should be included in that too.

Back in October/November 2020, I wrote a series of posts about what we know about SARS-CoV-2 and different animal species. It’s a dynamic field, so it’s about time I got around to updating them. We’ll start back at the beginning with one of the most susceptible domestic species: cats.  A lot of research about SARS-CoV-2 in cats in the last year has largely supported our initial observations and have helped refined what we know.

Are cats susceptible to the SARS-CoV-2 virus?

Yes, cats are clearly susceptible. No change here. We’ve known that for a while and more research has just solidified that. More on that below.

How often do cats get infected?

There are a lot of papers now about SARS-CoV-2 in cats. Some are very good. Some are interesting but low-impact single case reports, and some are rushed studies (“I want to be first, not the best”) that use small sample sizes, indistinct populations or cherry-pick interesting results from what should have been more comprehensive, bigger studies.

Overall, it’s apparent that human-to-cat transmission is common in households where people have COVID-19. A small number of studies have looked at active infection using PCR testing +/- virus isolation, which is tough to do logistically. It’s a lot of work to identify infected people, arrange to sample their pets and (typically) go to the household to do that. A study from Texas (Hamers et al. 2021) identified the virus in 3/17 (18%) of cats in infected households. The results of our Canadian study (which have been presented but not yet published) were fairly similar.

Testing for virus only tells us part of the story, because of difficulty with sampling infected cats soon enough to catch them during their short-term active shedding period. We assume that we often miss infections because we get into the household to sample too late. That’s why more studies are based on looking for antibodies in the blood of house cats as an indicator of previous infection. It’s less definitive than detecting the virus, since the performance of antibody tests can be variable, but with good tests it can really help our understanding of the situation.

When we look at antibodies to SARS-CoV-2 in cats in infected households, the apparent infection rates go up. The Texas study reported a seroprevalence (the percentage of cats with antibodies) of 44% (7/16), and the seroprevalence in our preliminary data from Canada was even higher at 67%.  Other studies have had variable results (for example,  a study from Peru found a seroprevalence of 17-30% among cats from infected households, depending on how the testing was interpreted), but the take-home message is that human-to-cat transmission of SARS-CoV-2 is pretty common.

There are also many studies that have looked at antibodies against SARS-CoV-2 in the general cat population, usually without any information about whether the cats were exposed to an infected person. These studies are fairly easy to do (for example, by testing leftover blood from samples collected for other purposes, or collecting convenience samples from cats presented to veterinary clinics or shelters), but their value is variable. Typically, these studies report low seroprevalence among cats. One study reported close to 10% prevalence, but <2% is more common (e.g. Dileepan 2021, Klaus 2021, Smith 2021, Stranieri 2021, Udom 2021, van der Leij 2021). Positives could be cats that actually had infected owners, but the information wasn’t known or collected, or false positives, due to an imperfect test. In our surveillance study of cats from shelters or spay/neuter clinics, we found there was often very limited history about the cats (e.g. cats recently acquired off Kijiji), so we can’t use the history to put the results into context.

There’s always a lag between disease occurrence and publication of reports, so it would be expected that rates of infection in cats would increase over time as the human pandemic continues and more cats become exposed.

Risk factors for infection in cats haven’t been carefully investigated yet, often because of fairly small study sizes. A Brazilian study reported that cats that slept in the bed were at higher risk of being seropositive (Calvet 2021), something we also found in our Canadian study. That’s not too surprising as things that increase close contact (direct or shared airspace) presumably increase the risk of human-to-cat transmission.

Do cats get sick from SARS-CoV-2?

They can, but most often if appears they don’t. Experimentally, clinical signs in cats have been pretty unremarkable. Most infected cats have been reported to be healthy, but it’s not always the case. There are reports of sick cats, including a paper describing a fatal infection in a cat in the UK.

In our surveillance, cats that had antibodies against the virus were more likely to have been reported as being sick at the same time as the COVID-19-infected owner, but most of the time any illness in the cats was mild (e.g. coughing, sneezing, quieter than normal). I get lots of anecdotal reports about sick cats that have been exposed to the virus, and I suspect many of them really are due to to SARS-CoV-2. When an otherwise healthy adult indoor cat with no contact with other cats develops signs of upper respiratory tract infection around the time its owner had COVID-19, there aren’t many other probable causes for the cat’s illness. However, at the same time, since infection of cats seems to be quite common, we’d expect to find incidental infection of cats that get sick or die from various other unrelated things. A small study by the US CDC (yet to be published) explored this, and the take-home message was that some cases of severe disease seemed to occur but much of the time, cats that died while infected didn’t die from the effects of SARS-CoV-2.

Similar to people, most exposed cats probably don’t get sick or get mild disease. A subset get more serious disease, and a smaller subset may even die from the infection. The relative size of those different groups is completely unknown.

Can cats infect other animals with SARS-CoV-2?

Yes. Experimentally, cats have been shown to infect other cats. That’s also been seen outside the lab, such as the high-profile outbreak in lions and tigers in the Bronx Zoo, where cat-to-cat transmission was more likely than all the big cats being individually infected by people. We also investigated one large group of infected cats, and it’s most likely there was cat-to-cat spread there too, rather than all human-to-cat infections.

Can cats infect people with SARS-CoV-2?

We still don’t know for sure if cat-to-human infection occurs. Since cats can infect other cats, we have to assume there’s some risk of them infecting people, but sorting out how much of a risk there is is a challenge. If someone got infected by a cat, it would be very difficult to determine that they got it from a cat vs a human contact, because the virus is still circulating widely in people, and contact with the infected cat would probably coincide with contact with that infected cat’s (probably infected) owner.

I think we have to assume that cat-to-human transmission is biologically possible and has probably happened. However, in the real world, it’s probably very rare given the dynamics of cat-to-human contact. If my cat gets infected, he got the virus from me, my wife or my kids. In that event, transmission from the cat to other people in the household is possible, but transmission between people is far more likely. Most cats don’t encounter a lot of different people, especially when their owners are sick. The biggest risk is likely when a cat leaves the house, such as to go to a veterinary clinic, or is surrendered to a shelter. We’ve detected infected cats in shelters, so it’s a plausible scenario, and it’s why we recommend asking about owner infection status prior to bringing animals into clinics, shelters or other places outside the home.

Do we have a SARS-CoV-2 vaccine for cats, and should we consider vaccinating cats?

My current answers are “kind of” and “no.”  There’s a SARS-CoV-2 vaccine (of unknown safety and effectiveness) licensed for use in cats in Russia.  In North America, there’s an experimental vaccine that has been used in mink and some zoo animals, and it would be the best option if we needed a vaccine. However, I don’t see a need at this point given the apparent rarity of severe disease. There’s more information on the possible utility (or not) of SARS-CoV-2 vaccines in pets in an earlier post. 

Could cats be an important reservoir of SARS-CoV-2 once it’s controlled in people?

Probably not. Cats are pretty susceptible to the virus, but they don’t shed it for long. To maintain the virus in circulation in the cat population, an infected cat would have to interact with another susceptible cat within a few days (and on and on…). Most cats don’t do that. In community cat colonies, I could see it spreading through the group, but it would likely burn out quickly as most of the cats became infected and recovered, assuming there’s some degree of immunity to re-infection (which seems to be the case) . In order to maintain a virus in a population when it’s only carried for a short period of time, you need a lot of animals and a lot of animal-to-animal contact. That’s more of a concern with some wildlife species (but that’s a story for another day).

Could cats be a source of new SARS-CoV-2 variants?

Probably not. Variants occur because of random mutations. These occur when the virus replicates. So, the risk of variant emergence is directly proportional to how much transmission (and therefore virus replication) is going on. Since we don’t expect sustained transmission in the cat population, there’s limited risk of variants emerging in there.

So, should we worry about SARS-CoV-2 in cats?

Worry, no, but we should pay attention to it.  There’s a cat health risk, and we want to avoid that by reducing contact of infected people with cats. It’s probably most important with older cats and cats with underlying diseases that may make them more susceptible to severe disease.

The risk of cats spreading the virus in a household is limited, but can’t be ignored. When you have someone isolating from the rest of the household (e.g. living in the basement), we want to make sure pets like cats are considered, so they’re not tracking the virus from the infected person to the rest of the family. It’s easy to see how someone might do a great job staying away from other people, but not think about the cat that runs back and forth between them and the rest of the family.

We also don’t want cats tracking the virus out of the household and exposing other cats or wildlife. The odds of this causing a big problem or creating a wildlife reservoir are very low, but not zero. A little prudence makes sense.  Keep cats indoors if they’re in contact with any infected people.

What should be done with cats?

This hasn’t changed from the first post….

  • Cats are people too, when it comes to SARS-CoV-2.
  • If you are infected, try to stay away from animals – all animals, human and otherwise.
  • If your cat has been exposed to SARS-CoV-2, keep it inside and away from others.

I figured I might as well hit double digits before circling back to update the earlier reviews of COVID-19 in animals. This group doesn’t get talked about much, but there are some important issues to consider with regard to non-human primates.

Not surprisingly, many non-human primates are known to be, or are likely, susceptible to SARS-CoV-2. In particular, it has been shown that the ACE2 receptor (ACE2) from apes, as well as African and Asian monkeys, is a good match for SARS-CoV-2. New World monkeys are likely not as susceptible because of some differences in their ACE2 receptors. Some lemurs are probably also susceptible.  See the Figure below from the ACE2 receptor study for more details.

My standard disclaimer is that ACE2 receptor assessment can be useful, but it doesn’t tell us the whole story. However, it’s probably fairly accurate here. Experimentally, rhesus macaques, and a few other species, have been shown to be susceptible to infection, as predicted by the shape of their ACE2 receptors.

The relevance of susceptibility is an important question. Specifically, what could it mean for the animals, and for people?

If SARS-CoV-2 got into a group of susceptible non-human primates, I’d expect a similar outcome as with introduction into a population of people. Some would be fine, some would get sick, and some would die from the infection. If the population is small and isolated, the virus would presumably burn out because it would run out of susceptible hosts in the short term and be eliminated. The more animals and the more contact they have with other groups, the greater the risk of longer-term persistence (and possibly mutation from being passed over and over again from animal to animal). My guess is this risk would mainly be sporadic and short term in specific groups.

The big concern is the potential impact on of an outbreak of SARS-CoV-2 in threatened animal populations, since an outbreak in a single group like this could be devastating for the overall population. Ebola had a huge impact on some gorilla populations – in fact Ebola virus was estimated to have killed up to one-third of critically endangered Western lowland gorillas overall, and 95% of individuals in some groups.  Transmission of human respiratory viruses such as respiratory syncytial virus, metapneumovirus and rhinovirus has also resulted in outbreaks (and deaths) in some other threatened populations of non-human primates. Clearly, if we can spread those respiratory viruses to our closest animal relatives, we can presumably do the same with SARS-CoV-2.

The risk TO people from COVID-19 in non-human primates is pretty low. The risk FROM people is pretty high. That’s why there are currently efforts to restrict contact of people with high-risk wild primate populations, including restricting field research, restricting access by tourists, increasing enforcement of boundaries (since human habitats often abut, or merge into, protected habitats), and requiring the use of masks and other preventive measures when people have to be in the vicinity of these animals. Strict infection control measures for SARS-CoV 2 are in place in some sanctuaries, such as those described by the Jane Goodall Institute.

Unfortunately there are also downsides to these precautions, including economic impacts for local communities, loss of research, difficulties with rehabilitation, and potentially increased poaching risks as there are fewer people around. However, the cost-benefit needs to be considered, and these measures are necessary to prevent potentially devastating disease outbreaks in these threatened populations.

What are the best ways to prevent disease from SARS-COV-2 in non-human primates?

  • Control COVID-19 in people
  • Reduce contacts between people and non-human primates
  • Control COVID-19 in people

Figure from https://www.nature.com/articles/s42003-020-01370-w

By the ninth installment in this series we’ve moved away from our familiar domestic animals, but there are still a few species worth highlighting.

Bats aren’t actually one species though, they’re a diverse group of over 1400 unique species. Some eat insects, some eat fruit, some eat small critters like frogs, and some eat blood (yes, vampire bats do exist, but no, they don’t die if they’re exposed to garlic or sunlight). One thing they have in common is they are all flying mammals that live in large groups.

Bats are obviously a concern when it comes to SARS-CoV-2 because this virus (as well as its close relatives, the original SARS virus and the MERS virus) likely originated in bats. Bats can be little coronavirus factories, but remember that there are huge differences between bat species. We shouldn’t talk about “bats” as the source of SARS-CoV-2, because we’re really talking about one particular species, Chinese horseshoe bats (Rhinolophus sinicus), as the likely source.

Just because a virus can infect one species of bat, it doesn’t mean it can infect them all. That’s important because bats are incredibly widespread internationally, and often travel long distances (and obviously aren’t stopped by international borders). We don’t want SARS-CoV-2 to spread to other bat populations. The more we can keep this a human disease, the better, since it’s easier to control a pathogen in one species versus many (especially when some of them can fly).  That’s one reason field research involving bats has been curtailed or suspended in many areas during the pandemic. We don’t want people getting near bats, as more person-to-bat contact increases the risk of exposing the bats to, and potentially infecting them with, SARS-CoV-2.  The odds of such transmission are pretty low to start, given the small number of people who do that type of work and their limited direct contact with bats; however, it’s a small risk with potentially very big implications, so curtailing field research for now is logical.

We also don’t know the potential range of bat species that might be susceptible to SARS-CoV-2. Predictive studies based on ACE2 receptors suggest that most bat species are probably not susceptible. However, many still might be susceptible.  We have to be very careful with these types of studies, as they’re useful but far from definitive.  As you can see from the figure below from one ACE2 receptor study, it actually predicted horseshoe bats aren’t susceptible to SARS-CoV-2, despite the fact they are a leading candidate for being the initial source of the virus.Experimental studies are one way to sort this out, but they aren’t common because they’re expensive and difficult to do with bats (let alone when you toss a dangerous virus into the mix).

One experimental study from earlier this year looked at susceptibility of Egyptian fruit bats (Rousettus aegypticus) and found that 7/9 bats exposed to SARS-CoV-2 developed a transient infection. One of three bats that were placed in contact with those bats also became infected. That’s a bit concerning, since this species can be found in parts of Africa, Asia and around the Mediterranean.

Research involving other common bat species is lacking. So, prudence would dictate that we treat all bats as potentially susceptible until we know they are not. There are a number of other reasons to avoid direct contact with bats as well (rabies being a big one), but keeping bats away from people and people away from bat habitats is particularly wise now.

To finish off… yes, bats can carry lots of potentially harmful viruses. But, they also do a lot of good things ecologically, like eating tonnes of mosquitoes (which are important disease vectors too). Don’t blame this all on bats. We (people) are the ones who got it from the bats and then spread it all over the world.

Image: Horseshoe bat (source: http://www.bio.bris.ac.uk/research/bats/China%20bats/rhinolophussinicus.htm)

This one’s easy. Birds are not susceptible to SARS-CoV-2. Stop reading here if that’s all you want to know.  If you’d like a little more detail read on…

The SARS-CoV-2 virus originated in mammals (most likely in bats, which will be the topic of the next review) and has spread to other mammals (especially people, of course). Birds are, well, birds, so they’re not mammals. Some viruses like both birds and mammals, but most don’t.

Researches have looked at this, and experimental infection studies have not resulted in evidence that birds are to any degree susceptible to SARS-CoV-2. This includes a study that looked at chickens, one that investigated chickens and ducks, and one that looked at chickens, turkeys, ducks, quail and geese.  Those fit with the predicted poor susceptibility of chickens to SARS-CoV-2 based on their ACE2 receptor (the cellular structure the virus uses to attach to and invade cells – no attachment, no infection).

So, why bother investigating birds, since it wasn’t likely that they’d be susceptible to a mammalian coronavirus in the first place?

It was really important to check and verify that birds are low risk for a few reasons:

  • There are massive numbers of domestic birds all over the world. That means lots of potential for exposure to infected people. If this virus got into a large group of birds (like on a poultry farm) and they were susceptible, there’d likely be big risks for the birds, as well as for transmission back to farm workers and issues with contaminated manure (just like we’re seeing in mink).
  • Jumps to new species in large groups is a perfect recipe for unpredictable mutations (which has also been a concern in mink).
  • Perhaps the biggest reason for wanting to know is simply that birds live everywhere we do, and beyond. There’s lots of potential for direct and indirect exposure of domestic (and wild) birds to this virus from human sources, and additional potential for contact between domestic birds and wild birds, which can then rapidly spread pathogens over long distances (as with avian influenza viruses).  So, we needed to be confident that this virus couldn’t establish itself in any bird populations.

That’s why the work was done quickly at the start, and thankfully birds seem to be completely resistant to SARS-CoV-2.

(All that said, if you have COVID-19, don’t cough in your bird’s face. The non-scientific part of my brain still never wants to tempt fate.)