I usually link blog posts to Tweets, rather than re-hash my Twitter musings (weese_scott) on the blog, but two things I posted on Twitter today may be of interest here.

COVID-19 in captive gorillas

Not surprisingly, COVID-19 has been identified in captive gorillas, in this case at the San Diego zoo.  It’s suspected that the gorillas were infected by an asymptomatically infected keeper, despite the intense precautions that have been taken to try to protect the animals since the pandemic began. It’s not at all surprising, since we assumed gorillas (and other non-human primates) that are relatively closely related to humans would be very susceptible to the SARS-CoV-2 virus, just like we are. With COVID-19 running rampant in California, it’s also completely unsurprising to have had an asymptomatically infected keeper at the zoo.

The more interesting aspect might be how the virus was actually transmitted from person to gorilla. Zoos tend to have very strict control measures in place to prevent this from happening (even when there isn’t a global pandemic), and the San Diego Zoo is an excellent facility. Figuring out how this occurred (e.g. inadequate practices, inadequate compliance) will be important to guide control measures at other facilities.

Toxoplasma gondii associated with brain cancer

Toxoplasma gondii is a protozoal parasite that has been linked to lots of issues in people, often with somewhat questionable evidence. Cats are the definitive host of this parasite, for which they get a very bad rap, but most human exposure is from the environment or food.

A recent paper has made some interesting but tenuous links between Toxoplasma infection and glioma, a type of brain cancer. It was interesting research, involving a large prospective study in which they collected blood samples from cancer-free people, and then followed them over time. After 13 years, they looked at the risk of gliomas in those who did or did not have antibodies against T. gondii prior to diagnosis (probably no real reason for picking 13 years… long enough for cancer to develop and it happened to be when they were ready to look at that).

There were some weak associations between one type of Toxoplasma antibody and development of glioma and glioblastoma. The data aren’t too convincing, but there are some similar results from elsewhere, which shows the subject needs more study.

What does this mean for cat owners?

  • Very little. Gliomas are a rare cancer, and while Toxoplasma exposure is quite common, it’s not usually from someone’s pet cat. Toxoplasmosis is a “don’t eat poop” disease, so there are lots of simple, routine things we can do to reduce the risk from pet cats (like not touching cat feces and washing your hands after cleaning the litter box).

More of my comments are posted on Twitter here: https://twitter.com/weese_scott/status/1348707854430167040

We have more information about Toxoplamsa on the Worms & Germs Resources – Pets page.

Here’s the latest version of our pandemic guidance document for Ontario veterinary clinics, produced in collaboration with the OVMA.  Previously entitled “A guide to reopening veterinary medicine in Ontario” it has been retitled “A guide to mitigating the risk of infection in veterinary practices during the COVID-19 pandemic (04-Jan-2021)“.

Previous versions of the guidance and other related documents can be found on the Worms & Germs COVID-19 Veterinary Resources page.


Not surprisingly, COVID-19 has been identified on a mink farm in British Columbia, Canada, in the midst of Canada’s 2nd wave of the COVID-19 pandemic.

It’s important note that so far, the virus has only been found in people on the farm, not in the mink. Eight farm workers were reportedly diagnosed with COVID-19 over the weekend, so now testing of the mink is underway. With 8 infected people at the facility, it’s pretty likely that the mink are infected as well, since they are quite susceptible to the SARS-CoV-2 virus, but we’ll need to wait for the test results later this week.  If there are a few infected mink on the farm, that can become lots of infected mink pretty quickly.

This is a breaking story so more information will no doubt roll out over the next few days.

The big questions are:

Have the mink been infected with SARS-CoV-2?

  • We’ll know soon enough.

Has there been any mink-to-human transmission of SARS-CoV-2?

  • That’s a bit harder to discern, especially if all of the infected workers have had contact with each other. If the virus is detected in mink, sequence analysis and comparison of the strains in the mink versus the workers will be part of the picture.

Has/will the SARS-CoV-2 virus mutate in the mink (as was seen in Denmark)?

  • We’re still unsure about how much of a risk virus mutation is.  Mink farms have  large numbers of susceptible animals, making them good places for mutations to occur. Virus mutations are random events, so they may be good or bad. We’re worried about mutations that negatively impact control measures (like vaccination) or that could make the virus more transmissible or illness more severe IF the mutated strains spill back into people. As above, sequence analysis will be used to look for evidence of significant mutations.

Have other animals on or around the farm been infected with SARS-CoV-2?

  • Testing of any other animals on the farm (e.g. cats) and wildlife on the property will likely follow if the mink are found to be infected.

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.)

Headline:  “Are Dogs Spreading SARS-CoV-2?  Study Finds Living With a Dog Increases Risk of Contracting COVID-19

NO, it did NOT!

Even though the paper said that, it’s not what they actually found.  Unfortunately, a lot of people are reading that headline, or worse, they’re reading “…yada yada… dogs spreading SARS-CoV-2… yada yada.

What did the study really find?

Let’s break down some important aspects of the paper on which this headline is based.  The study, entitled “The spread of SARS-CoV-2 in Spain: Hygiene habits, sociodemographic profile, mobility patterns and comorbidities“(Rodriguez-Barranco et al. Enviro Res 2021), reported that people who walked their pets were 78% more likely to have reported having had or maybe had COVID-19.

  • They didn’t investigate that any further, and it’s not clear what “walked their pets” entailed (e.g. walking a dog once outside the house vs walking a dog on a regular basis).
  • The question, strangely, asks about walking “pets” not “dogs.” It’s reasonable to assume that the pets were at least mostly dogs, but they didn’t actually specify that.
  • How the authors analyzed the data is also unclear. The answer options for the pet-walking question were yes / no / I don’t have a pet. However, for analysis, they combined pet owners who didn’t walk their pets and non-pet owners (further demonstrating that they did not look at the risk of living with a pet).
  • They said that 6.9% of people who walked their pet had been infected, vs 4.2% of those who did not take their pet for a walk, despite the fact that most of the latter group actually didn’t own a pet at all.

So what they really looked at was leaving the house with a pet (vs living with a pet), and that raises some serious questions about how clearly they thought about the results. The focus should be on the “going for a walk” component, since that’s what they actually studied. Unfortunately, they didn’t also ask if people went for walks without pets.

Some of the other study results also raise more questions than answers:

  • They reported that people who used home delivery for food were almost twice as likely to have had COVID-19. Does that mean they were getting infected by delivery people and would have been safer shopping? Presumably not.  My concern is that there was some reason that people were more likely to order food, and that was also a risk factor for COVID-19. For example, if they knew they had been exposed or were in some other high risk situation, that might lead people to avoid stores and also be at higher risk of being infected.
  • Another big issue is the fact that people with COVID-19 were presumably more likely to order delivery after being diagnosed. The survey doesn’t ask what they did BEFORE getting infected (if they had COVID-19), just what they did during Spain’s period of restrictions. So, finding increased risk from home delivery might actually be because people who were more likely to use home delivery were otherwise higher risk or already had COVID-19.

Another concern is who they surveyed. The study population is critical for any study like this. You need to understand the study population to understand the results and any potential bias. You can get really misleading information or not understand your results if you don’t understand the group of people that provided them and how they compare to the general population.

Why is the study population so important? Here’s an over-the-top example to illustrate:  Let’s say a study said “pet owners were significantly more likely to say their dog was an important part of the family compared to cat owners,” but the study only enrolled people through websites like www.ilovemydog.com and www.mycatisademonicpsychopath.org – you can see how we might end up with a biased understanding of the situation.

In the discussion of the Spanish study, the authors mention that most respondents were graduate or post-graduate students, which is a pretty specific group. We have to consider how well they represent the general population. The farther away they are from average, the less confidence we have in extrapolating results to anyone other than graduate and post-graduate students.  I’m not saying there’s a problem using this study population. What I’m saying is we just don’t have enough information to know what it means. That’s one of the (many) things I’d flag reviewing a paper like this.

Survey response rate (and response bias) is also an issue, but I deleted my detailed comments on that since this post is already getting quite long (and probably a bit dry).

The way the authors wrapped things up is a big issue for me.

In the discussion they say, “These results point to living with dogs as a strong risk factor for COVID-19 infection.” Their concluding statement was, “The results of this study demonstrate that living with dogs… have been the main routes of transmission of SARS-CoV-2 during the most restrictive period of confinement in Spain.”

Neither of those is true.

Pet ownership was not associated with increased risk of COVID-19. Their statistical analysis of pet ownership did not identify any risk. Walking a pet was a potential risk factor, not owning or living with a pet. There’s a long paragraph in the discussion talking about risk from dogs, despite the fact the paper didn’t actually look at that, and they did not find a risk from pet ownership.

So, what does this study tell us about pets and risk of COVID-19?

It’s hard to say… probably nothing.

This study raises some interesting questions but doesn’t provide many answers. It certainly doesn’t provide answers about risks associated with pets. A more rigourous peer review could have helped catch and address some of those issues.

The study does NOT show pet ownership was a risk factor for COVID-19.

  • If the pet walking risk factor is real, I suspect the critical factor is more “walking” than “pet.”

I’ll stick with the same messaging I’ve had for months about animals and COVID-19:

  • If you have or might have COVID-19, stay away from animals (human and non-human).
  • If your pets have been exposed to someone with COVID-19, keep them away from others (just like you would if you or your kids were exposed).
  • Relax.

I’m going to have to go back to the start soon and update previous reviews of COVID-19 in animals, but there are still a couple of more species worth mentioning first. Cattle are an obvious consideration because they are important food animals that are widely raised in countries around the world, and they are often housed in large groups. Some cattle, especially dairy cattle, have a lot of contact with people. More human contact means more risk of exposure to the SARS-CoV-2 virus, and more animals in a group means more risk of animal-to-animal spread (and possibly mutation of the virus, as has recently been seen in mink in Denmark).

Fortunately, the SARS-CoV-2 virus doesn’t seem to like cattle. We probably can’t say they’re not susceptible at all, but based on what we currently know we can say they’re minimally susceptible at most. In terms of spread of SARS-CoV-2, the risk to cattle is minimal, and the risk to people from cattle is pretty much zero.

There was some interest in determining if cattle were susceptible at the start of the pandemic, because cattle are susceptible to bovine coronavirus, which is also a beta-coronavirus, just like SARS-CoV-2. However, cattle were predicted to be low-risk for infection based on the form of their ace2 receptor, the site the virus uses to attach to and subsequently infect cells.  Predictions from these receptor-based studies haven’t always been accurate, but they seem to be true in this case. One experimental study in cattle has been reported so far (Ulrich et al.), and it supports the notion that cattle are pretty resistant to infection with SARS-CoV-2.  The researchers found that viral RNA was transiently detected at low levels (likely not enough to be infectious) from nasal swabs of 2/6 inoculated cattle, and those two animals developed a very low level of antibodies as well. No cattle that were co-housed with the inoculated cattle became infected. In summary, there was some degree of infection that stimulated the immune system to respond in two animals, but it was a minimal response.

As usual, the two important questions are:

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

  • We have a single study of 6 cattle of one type and age, which is far from definitive, but it doesn’t indicate any health risk to cattle.

2) Can infected cattle shed the SARS-CoV-2 virus? (and therefore pose a risk to other animals, including humans)

  • Virus shedding in cattle doesn’t appear to be a concern. Even if the odd cow can be transiently and mildly infected, it’s very unlikely they would shed enough virus to pass it along to another animal or person.

So, let’s not ignore cattle completely, and let’s still try to keep infected people away from them, but we can probably relax when it comes to SARS-CoV-2 and this particluar species.

Denmark is one of the largest mink producing countries in the world, and mink on numerous farms have been infected with SARS-CoV-2 from farm workers with COVID-19. At last report, 216 farms were affected. That wasn’t too surprising since outbreaks on mink farms have been seen in several countries, with particularly widespread infection on farms in the Netherlands. The issue is a recent report by the Serum Statens Institute (SSI) and some government releases about emerging “mink strains” of SARS-CoV-2 and a large number of human infections with a “mink strain.”

Crap.  Mutated virus. That sounds bad.

Not necessarily. Viruses mutate all the time. It’s a random event. It’s more likely to occur when there are large numbers of infected individuals, simply because there are then more opportunities for random mutation. A mink farm with thousands of closely housed and highly susceptible mink is a great place for that. It’s also probably more likely when a virus moves between species, as some random mutations might make it easier for the virus to infect their new host species.

So, what’s going on with SARS-CoV-2 in mink in Denmark?

At this point, five different variant strains of the virus have been found in mink, which include variations in the spike protein the virus uses to attach to (and subsequently infect) cells. If such a mutation makes it easier for the virus to attach to cells of a given species, it becomes more infectious to that species. Conversely, if a mutation decreases the ability of the virus to attach to cells, it makes the virus less infectious. The spike protein is also an important vaccine target, raising some concerns about whether mutations could decrease the effectiveness of some vaccines that are being developed (a bit more on that below).

One particular variant has been found in human samples too, some from people that are connected to the mink farms, and some from people who aren’t.  The variant strain has been found in 214/5102 virus isolates from people, 94% of whom are in North Jutland, where most of the infected mink farms are. This variant accounted for 40% of the isolates in that area, which is pretty impressive (not in a good way).

A translation of the Danish SSI report about the emergence of these variants in mink and their spread to the human population says “SSI estimated that continued mink breeding would entail a significant risk of recurrence of a large spread of infection among mink and humans, as seen in Western Denmark in 2020. SSI estimated that this would pose a major risk to public health. Both know that the many infected mink farms can lead to a greater disease burden among humans, and know that a large virus reservoir in mink increases the risk of new virus mutations occurring again, which vaccines may not provide optimal protection against. Overall, the immunity gained through vaccination or past infection may also be at risk of being weakened or absent. The overall conclusion, which was also supported by the Danish Health and Medicines Authority, was therefore that continued mink breeding during an ongoing COVID-19 epidemic entails a significant risk to public health. Including the possibilities for optimally preventing COVID-19 with vaccines.”

Is this really a “mink strain” of SARS-CoV-2?

It’s hard to say. It’s a strain that has been found in mink. It might have mutated in them or it might have mutated in the person that infected them. Most likely, it did evolve in the mink, spread to people, and then those people spread it to other people.  Everyone’s talking about it like it’s one strain, but there are actually several strains linked to mink now. One is getting the most attention, though.

How did hundreds of people get infected with this strain? Are mink everywhere in Denmark?

No, mink aren’t everywhere, but people are. This is a situation where (I assume) most of the transmission is still human-to-human. It came from people, probably changed in the process of being transmitted between so many mink and then was likely transmitted back to a few people with close contact with the mink, and is now back to being transmitted widely between people.

So, why do we care?

  • Anytime we see movement of a virus into another species, it’s a concern. Mink infecting people isn’t the real problem, since few people have any direct contact with mink. The issue is whether mink can complicate overall control of the disease in people. More species involved means more problems to address. Denmark was already culling affected and neighbouring farms, but as more mink farms get infected, that creates more opportunities for new strains to emerge.  So they’ve now made the difficult decision to cull all farmed mink in Denmark until the COVID-19 pandemic in people is under control.
  • Related to the above, the last thing we want is this virus in wildlife. Transmission to cats has been found on mink farms in the Netherlands, Fortunately, so far, we haven’t seen issues with SARS-CoV-2 infection in wildlife (but we didn’t see issues with mink either until we suddenly had a big issue with mink… if you catch my drift). Mink create a potential bridge to other species, and we don’t want that.

And the big one….

  • Is this mutation a problem for people? Early lab data suggest that this virus isn’t neutralized as well by antibodies from people infected with the more common strains found in the human population. That could impact the effectiveness of antibody-based treatments or vaccines, but it’s too early to say there’s a relevant issue. It’s certainly something that needs to be investigated as if it’s relevant. If it impacts vaccination, we start getting into a situation where we might need a vaccine that protects against multiple strains of SARS-CoV-2 (and none of the billions of dollars in vaccine development money has been spent looking at this new strain).

Some new outlets have talked about the chance for a “new pandemic.” Is that realistic?

No. Our current pandemic is doing just fine and isn’t going to be displaced. We are effectively transmitting the original virus between people, and we will probably effectively transmit this other strain too. It’s not likely to change the character of the pandemic (unless it impacts treatment or prevention). There’s no evidence that it causes more serious disease.

What does this mean in the big picture?

It’s too early to say. Whether this is an academic curiosity, a mutation that might lead to some interesting epidemiological data but has no additional health impact, or is a sign of a looming problem, is hard to say.

What do we do?

  • Relax.
  • Avoid kissing mink (most mink would eat your face if you tried, anyway).
  • Continue to pay attention to animals as potential sources of infection.
  • Most importantly: control human-to-human spread. The best way to prevent the spread of mink-strain COVID-19 is to prevent spread of COVID-19. Period.

In the big picture (jumping on my soapbox for a moment), this is why I’ve been saying these things since January. It’s why we criticized groups like CDC that said “there’s no evidence animals can be infected” before there was any effort to find out. We need to approach emerging diseases proactively, by looking for potential problems and taking steps to control them early, rather than waiting for definitive evidence of a problem.

Photo by Markus Winkler on Unsplash.

Perhaps this is one you didn’t see coming, but there have been lots of discussions about SARS-CoV-2 and marine mammals. You may think, “people don’t have much contact with marine mammals,” and of course you’d be correct, if you meant direct contact. However, human activity (and waste) can significantly influence marine mammal health.

What’s the risk of direct transmission of SARS-CoV-2 from humans to marine mammals?

This is a concern for a very small group of people, but human contact with marine mammals  does occur, with both captive animals and sometimes during field studies. Any direct contact poses some risk of transmitting pathogens (of many kinds) in either direction. We saw human-to-marine mammal transmission a few years ago during an MRSA outbreak in dolphins and walruses that we investigated.  If people can pass MRSA to marine mammals, we can presumably do the same with the SARS-CoV-2 virus. However, in the grand scheme of things, infection of captive marine mammals is of limited concern (at least beyond the individual animals in a collection).

How would wild marine mammals get exposed to the SARS-CoV-2 virus?

The main issue is exposure of marine mammals to the virus via sewage. The virus doesn’t like being outside of a warm body, but it will survive for a short period of time in sewage. Unfortunately we don’t know exactly how long it can survive in such waste water, or how different sewage treatment approaches influence survival of the virus.

We know that exposure to human sewage can result in transmission of pathogens to wild animals, so the concern isn’t unrealistic in areas where there is close proximity of marine mammals to human sewage effluent, especially if there are sewage infrastructure challenges that lead to release of poorly treated or untreated sewage.

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

We don’t know. As I’ve discussed before, we can look at their ace2 receptors (structures the virus uses to attach to and invade cells) for clues. We have to be cautious putting too much faith in predicted susceptibility based on ace2 receptors, and most of these studies have not included marine mammals anyway. However, a couple of studies ranked various marine mammals (including a variety of whales and porpoises) as having potentially “high” susceptibility (Damas et al., Luan et al.).

There is a pre-print available of a marine mammal-focused study modeling potential susceptibility to SARS-CoV-2. Th study predicted various whales, dolphins, seals and otters would be highly susceptible to the virus. Sea lions were lower risk, which would be a very good thing given how they congregate in large populations, often close to human populations. In contrast, the models predicted some species like beluga whales and bottlenose dolphins may be even more susceptible than people. High-risk species included a large number of species that are already vulnerable or endangered.

Overall, the risk to marine mammals is likely very low, especially in terms of creating a sustained problem.  This virus isn’t as hardy as most pathogens that we know can be spread via sewage. If infected, infected marine mammals would likely only spread the virus over short distances and short periods of time. A small pod of whales poses much less risk overall than a large population 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 population could still have significant consequences.

Is there a risk of SARS-CoV-2 transmission 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 doing it in ours. Sure, an infected marine mammal would likely pose a risk from direct contact, but the odds of such contact are very low.  Outside of some very densly populated areas, I suspect the potential impact of marine mammal infections (should they occur at all) on human health is very low.

What are the recommendations with regard to marine mammals?

  • We need to learn more about sewage, as an indicator of infection of people in the community, but with that we should also aim to learn about the potential for viable virus escaping into nature and exposing wildlife (both terrestrial and marine). Detection of viral bits in sewage by PCR is one thing. Knowing how that correlates to infectious virus is key to assessing the risk of spillover into wildlife.
  • The risk of human-to-animal transmission can’t be ignored. Facilities with captive marine mammals should limit contact with them (just like they should be limiting human-to-human contact), and obviously there should be no contact with people who are infected or quarantined because they are high-risk.
  • Similar precautions apply to field research. This has been a tough topic for any field researcher, but the goal is to prevent problems, not react to them. So, we’re better off limiting direct contact with wild mammals (both terrestrial and marine) as much as possible. When contact 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.

Image source: https://www.news-medical.net/news/20200817/SARS-CoV-2-poses-significant-threat-to-many-marine-mammal-species.aspx