This is less of a content update and more of a “here’s what I really want to know,” but it’s still an update, I guess. It’s a bit hard to say where we currently stand with this problem, at least in terms of the most important aspects. That’s not uncommon with emerging diseases, but we’re in more of an information vacuum than I’d like.

What do we know about the current outbreak of H5N1 influenza in dairy cattle?

The case count keeps going up, but there aren’t a lot of details available about the new cases; some media reports about new cases have actually been quicker and more comprehensive than USDA reports. Currently, I think we’re at 21 confirmed infected dairy herds in 7 states. I’m guessing there will be more affected herds, possibly in more states, that we’ll hear about in the near future, as there’s no doubt some reporting lag, there could be continued spread, and in some cases it may be a matter of slower identification of ongoing problems. The latest USDA map is below, but it’s missing the most recent state to identify a dairy herd with H5N1 influenza, North Carolina. The total number of animals affected isn’t reported, but that’s not as important as the farm and state numbers that tell the bigger picture.

What do we not know about the current outbreak of H5N1 influenza in dairy cattle?

Hopefully it’s more of a “what’s not being released” versus “what’s not known” – presumably there’s more information somewhere than what’s been released. That’s not uncommon in a situation like this. Sometimes there are good reasons for certain information to be kept within certain circles, such as information that may be very sensitive or data that are still just preliminary. Sometimes, the information would just be for interest’s sake, but not particularly critical for the average person or stakeholder, so there’s no urgency to release it. But all too often, there’s too much restriction, resulting in information that could inform action being withheld or only slowly released. With emerging diseases, we need balanced and effective action, and if we lack important details, we can’t tailor the appropriate response.

What do we need to know about the current outbreak of H5N1 influenza in dairy cattle?

Inter-farm transmission: We really need to know how this virus is spread.

  • If spread between farms is based on movement of cattle, we can intervene through changes in how cattle are moved and how they are handled after being moved (e.g. isolation requirements at a new farm). We can think about testing associated with cattle movement (e.g. if you’re buying a cow from another farm, test if before it leaves +/- after it arrives) and biosecurity practices to prevent a person from tracking the virus from another farm. This scenario would also suggest that aggressive action now could result in at least temporary eradication of this strain in cattle. Since we don’t have (as far as we know) long term carriers of flu, if we contain the virus on an infected farm, it should die out. If we contain transmission on farms and transmission between farms, we can (theoretically) get this flu strain off farms altogether.
  • If the cases that are occurring on different farms across different states involve repeated wild bird-to-cow transmission, our risk and management approaches are different. It would mean that keeping a closed herd (not allowing new cattle in, and using good biosecurity practices with workers and visitors) would not be enough to prevent exposure. Even if we locked down the affected farms, cattle could still be exposed by contact with wild birds. Preventing exposure to wild birds is really tough on a dairy farm.

From a Canadian standpoint, this is also really important for our risk assessment. If it’s just farm-to-farm spread, we have limited risk of it being tracked across the border if the industry adheres to good basic biosecurity practices. If there’s ongoing spread by birds, we will almost certainly have it up here before long as the spring bird migration continues.

This also ties into the risk to beef cattle. If this strain is being spread by wild birds, beef cattle will be exposed. If it’s being spread via dairy cattle, beef farms will have very limited risk (apart from buying in surplus dairy calves).  

Genomics: Understanding the makeup of the virus is important for a few reasons.

  • Does the strain infecting dairy cattle have more mammalian adaptation markers? There are some genetic changes that make flu more able to infect and transmit between mammals, including people. We want to know if these are cropping up as the virus gets transmitted to more and more cows. The virus is currently a long way from being able to readily infect people, but we need to keep looking to know it’s not continuing to change.
  • Are the strains found in cattle in different states the same? And are they different from birds in some of those areas? This would help sort out the route of transmission. If the virus in cattle from different states is basically identical, and particularly if the strain found in birds from each of those areas is different, that suggests it’s spreading via movement of cattle. If there’s more genetic variation between isolates from cattle in different states, and the strain in one herd is more like those from birds in that state than cattle in another state, it suggests that bird-to-cow transmission is playing a bigger role.

Intra-farm transmission: We could also use more details about how the virus moves around within a farm. It’s been reported that cows seem to mostly shed virus in their milk (with very little in their respiratory secretion), and that transmission between cows on a farm is therefore likely via milking equipment. Having some on-farm epidemiology to support this would be nice. If milk is the main source of transmission, there might be some corresponding disease patterns in the milking cows. I’d also expect to see no (or very few) infections in non-milking cows (i.e. younger animals (heifers) that have not yet calved, older cows that are between lactation cycles). Young calves could also be an interesting part of the story, looking at whether there have been infections in this group, and if so, whether those calves have been fed discarded milk from potentially infected cows (milk from sick cows is not allowed to go into the bulk tank for shipping). If infections are found in non-milking animals, we need to figure out how they might have been infected, because it helps us figure out if the infection control emphasis on farms should be with milking practices or if we have other issues with which to contend.

Cattle illness: More information about what clinical signs H5N1 virus causes in cows would be helpful. Some information has been released, but it’s sometimes vague, and I’ve seen conflicting information about illness being very mild versus fairly severe but short-term, and very obvious mastitis. Knowing the typical signs and range of disease is important for farmers and veterinarians on the lookout for disease. More details about test results are also important, particularly whether the early reports of the virus being present at high levels in milk but not in respiratory secretions are holding. That has major implications for transmission, and therefore infection control measures.

Infection in other species: I assume there’s been testing of other animals on these affected farms. It would be useful to know the numbers and results; negative results are as useful as positive results. It was reported that there were affected cats on at least one of the Texas farms. Is that unique or common? Have there been other positive farm cats? Were they sick, and if so what signs of illness did they show? If not, how many cats have been tested and were negative? This has both animal and human health implications. From a veterinary standpoint, I want more information about disease in other species, both to help care better for those animals and to protect people working with them.

Infection in humans: Obviously, we’re worried about human infections. How many people have been tested, and how many have been monitored in terms of their health?

  • If they are monitoring +/- testing hundreds of people with regular contact with cows and their milk, and no one has been sick, that’s great, and it’s important information to gauge risk for others.
  • If there’s limited surveillance and testing in people, we can’t be as confident about the risk.

Concerns have been expressed about the willingness of tenuously employed (and sometimes undocumented) workers reporting signs of illness, so “we haven’t heard of any more sick people” really isn’t a good enough answer in this scenario. Hopefully there’s a robust surveillance program in place, but that’s not something I’ve seen described.

Hopefully a lot of this information is available at least within certain circles, and simply has not yet been released publicly. If that’s the case, hopefully it will be released soon. As I said, there are some reasons to hold some data, but in general, more transparency and more communication makes for a much better response, and also helps to assuage public concerns, fears and mistrust.