Bird Flu Outbreak in U.S. Dairy Farms

UPDATE

If you have not read my two prior blog posts on avian influenza (bird flu), you will want to do so before reading this update because I am just going to jump into it without providing an refresher.

For the first time to our knowledge, an avian influenza virus [in this case A(H5N1)] is spreading among dairy cows. At the moment, it seems to be only happening in the U.S., but this is a quickly evolving situation, so that may not be the case for long.

There are now at least 25 outbreaks in 8 states: ID, KS, MI, NC, NM, OH, SD and TX.

There are many unanswered questions and much we must learn because while at the moment the risk of spillover into humans seems rather low and primarily a risk for those who work on farms and are in close contact with infected animals, were the virus to further adapt to efficient human transmission, this could potentially cause a very serious pandemic. That is in large part because the human population has no existing immunity to this virus. The seasonal influenza viruses we have been infected with and the viruses that have been used for our vaccines are all distinctly different from this strain of virus and would not serve to protect us from infection or severe disease with this avian influenza virus.

On the reassuring side of things, while it was initially feared that cows were transmitting the infection directly to other cows, USDA animal health inspectors now believe that is unlikely. There are two potential sources of transmission being evaluated.

One is related to a practice in the U.S. that reprocesses chicken waste and feeds it to cows. This is outlawed in many other countries. Avian influenza primarily infects waterfowl and they in turn primarily infect domestic birds and poultry. Many viruses are excreted in the waste, and of course, this is one of the reasons we have found great utility in wastewater testing for many viral diseases. The chicken waste that is being fed to dairy cattle needs to be tested to see if there is infectious virus in it. If this is the culprit, this might help explain why there are so many outbreaks in dairy farms across the U.S., but not in countries that have outlawed this practice.

It should not be glossed over how surprising aspects of these recent outbreaks are. As Thijs Kuiken, a professor of comparative pathology at Erasmus Medical Center in Rotterdam, Netherlands stated: “I want to emphasize really how unusual this is. In other mammalian species with influenza viruses, it’s primarily a respiratory disease, which doesn’t seem to be the case in these cattle.”

Changes in transmission modes of viruses are quite unusual. We saw an example of this with Mpox (formerly known as monkeypox). So, too, we are witnessing something distinctly unusual in this case.

Besides the reprocessed chicken waste feed, the other leading theory is that the virus may be transmitting among cows by the milking equipment given that the virus is detected in high levels in the milk of infected cows.

Obviously, there are immediate steps that can be taken:

1. The USDA could halt the use of chicken waste feed for cattle until tests are done that ensure it is not the route of infection.
2. We need to ensure that there is appropriate cleaning of milking machinery prior to use on another cow.
3. Personal Protective Equipment (PPE) including goggles (the eye is the only place identified thus far that has suitable receptors for this virus in humans) for farm workers.
4. Limiting movements of cattle and isolating cows at the first signs of illness.
5. Routine, screening testing of cattle and other animals on farms.
6. Increasing our supplies of antivirals, or at least having plans in place for streamlining manufacturing, production and distribution so that supplies of these antivirals could be greatly increased and quickly accessible in the event needed.
7. I previously wrote that the CDC and FDA need to determine the effectiveness of avian influenza vaccines already in our National Strategic Stockpiles against the current strain of virus circulating in cattle. Even though we have limited supplies, perhaps we would have enough to immunize farm workers. We have FDA-approved H5N1 vaccines from 2013, 2017, and 2020.  However, testing has revealed that these vaccines do not elicit a protective immune response after a single dose. Unfortunately, even after a second dose, it is unclear that the immune response is sufficient to protect against severe disease. This is an area that needs to be the focus of intense research effort to identify targets for effective and durable immune protection against this particular virus.