Has Bird Flu Flown the Coop, or is It a Problem Still to Be Reckoned With?

By Phil Durst

In Michigan, a number of cases of Highly Pathogenic Avian Influenza (HPAI), commonly referred to as “bird flu” affected dairy herds during the spring of 2024. Since then, new cases reported during the summer months have decreased to a total of six over five months in four counties (Clinton, Gratiot, Van Buren and Shiawassee). While these may not be all the positive farms, certainly it appears that the number of confirmed cases have been more sporadic.

National spread of HPAI

However, USDA reported 43 confirmed cases nationally during the month of September, many of which were in California where reports showed herd infections occurring at a fast rate (reportedly 16 dairy herds between September 18 and 23). The bottom line is that the risk is not over, the disease has not passed, and farmers should be diligent.

There is much we have learned since HPAI was first identified as the cause of the symptoms seen in cattle herds in Texas and Kansas in late March 2024. What we know at this point is that when a herd becomes affected, it can spread rapidly with the incidence peaking 4-6 days after the first animals are affected, and that it is most likely to affect older cows (> 1 lactation) in the mid to late stages of lactation, according to “Highly pathogenic avian influenza A (H5N1) virus infection in domestic dairy cattle and cats,” by Burrough, E. R. et al.

From the experience of farms that have had HPAI, we know that feed intake drops, rumination decreases and milk production, therefore, drops rapidly. Most cows recover, and herds recover within weeks. Farms have reported some abortions (likely due to high fever), some increased culling and certainly higher labor and veterinary costs. While it may come and go, the disease leaves behind a bill for services of approximately $200,000 in a 1,000 cow herd from lost milk, greater labor and increased costs.

While we have learned much about the action of HPAI that helps us to react, it is what we don’t know that doesn’t help us, and there is much we don’t know.

The unknowns of HPAI

We know that the milk of an affected cow often has a high level of active virus. Though it has not yet been shown, it is believed that milk is a primary way the virus is spread on dairy farms during the milking process. In fact, the virus may spread for a week or more before symptoms are observed on farms. There may be brief respiratory disease at the start of infection, but that remains to be proven and whether it is a significant factor in spread of the virus on farms is not clear.

While the virus has not been found in cow manure, manure from a farm pit often contains waste milk or milking equipment washings that may have the virus, thus providing another means of potential transfer of the virus. The virus is apparently resilient and able to survive in the environment for days at the least.

We know that animals can be asymptomatic carriers and shedders of the virus in their milk, but whether there are a significant number of these or if it is a significant factor in disease spread, we don’t know. We don’t know if animals develop a robust immune response to the disease and if so, how long it will protect them from reinfection? We don’t know why older cows and cows in later lactation are the ones most likely affected. And we don’t know the risk of a herd reinfection.

The answer to these questions really will only be known through herds reporting disease and being willing to undergo testing. Farmers hold the key to more knowledge about the disease so that more herds can be protected.

First responses

Reacting quickly to suspected disease is critical. If a farmer thinks that their herd may be affected, it is best to voluntarily contact their veterinarian who will report it to the state department of agriculture. Isolate animals showing any signs of the disease (fever, reduced milk), provide supportive therapy with approved NSAIDS to reduce fever and help the animal be more comfortable.

Practice good biosecurity as discussed in MSU Extension’s Biosecurity for dairy and beef cattle farms. This is a disease that can move between farms, even without moving cattle. We don’t fully understand how it moves, but the evidence is there. It can also move to poultry operations, whether backyard or commercial and will be quite lethal in those flocks. Quarantine incoming cattle for 21-30 days to monitor for disease break. Fewer and clean vehicles and people coming onto the farm and clean vehicles and people leaving the farm are keys to biosecurity.

Biosecurity always depends on people, people who are trained and consistently practice the risk-reducing steps of the plan. Farm owners need to monitor biosecurity to make sure that it is being implemented and frequently train or talk about biosecurity.

Testing programs, such as USDA’s program of bulk tank testing for three consecutive weeks are valuable to determine a negative herd status and enable moving lactating cows across state lines. For herds which depend on moving lactating cattle, weekly bulk tank samples after the initial diagnosis of a negative herd, are necessary to allow movement without individual animal testing.

Be alert

As time goes on, it is easy to become insensitive to the information about HPAI and the risks to one’s herd because of information overload. But there are some things that should cause one to take notice. On the farm, the presence of dead cats often goes hand-in-hand with a herd infection where cats have access to raw milk.

On a national level, be alert to these potential developments:

1. Commercialization of a vaccine for H5N1genotype of HPAI. In early September 2024, USDA approved one company to conduct field trials for a vaccine to prevent infection with this strain of the virus. A vaccine would be a tool by which to reduce risks to a herd.
2. Availability of an ELISA test for HPAI. ELISA tests are commonly performed on milk or blood serum samples to detect antibodies against a pathogen. Currently, the problem is that milk samples would potentially contain the virus that could infect those who either take the samples or those who work on them in the lab. For the test to become available, the problem of virus pathogenicity must be solved.
3. Report of HPAI infection in a swine herd. While this has not occurred, the H5N1 virus is prone to mutate in cattle. Mutations are a natural response that enables the virus to survive. If a mutation occurred that enabled the virus to infect swine, the risk to humans would become much greater than it is currently.

HPAI is still a threat to dairy herds. It has a cost and carries a burden for farms. It seemed to have appeared out of nowhere when the diagnosis of this disease was attached to the problems experienced by herds in Texas and Kansas. The reality is this will not likely be the last herd infection to threaten dairy cattle. Daily practice of good biosecurity is important. For those who believe it is burdensome to practice biosecurity, the burden of the disease is greater. Reducing risks should be a conversation that every farmer has with their veterinarian, Extension educator and with their employees.