-Carie M. Telgen DVM, NEAFA Board Member
The Avian Influenza H5N1 virus continues to wreak havoc in parts of the United States. As of July 18th, there have been 164 confirmed cases in 13 states, with the latest confirmed cases reported on July 17th. To date, there have been no positive cases identified in the Northeast Region. However, there are new infections daily that are not only affecting dairy farms throughout the mid-west and plains states, but neighboring poultry flocks. Since the outbreak, millions of chickens and turkeys have been euthanized due to this outbreak. Although H5N1 does not cause severe disease in dairy cattle, it is often fatal to poultry flocks and has far reaching implications when poultry flocks are infected.
As the entire agricultural industry continues to try to understand how this virus is behaving in dairy cattle that is different than other species, universities and governmental agencies are actively researching various aspects of the disease. USDA National Animal Disease Center recently completed two pilot studies, that are currently in pre-print, in an effort to understand modes of transmission of H5N1. In the first study, using a nebulizer, they inoculated yearling Holstein heifers and evaluated disease progression and symptoms. After 21 days, the heifers were necropsied, and various pathological samples were tested. Results of this study showed that the respiratory disease was mild and sporadic. Heifers were sero-converting as early as 7 days yet; it took a variety of samples to identify virus in the respiratory system. This indicates that aerosol transmission is possible, but much more sporadic and less likely than other modes.
In the second study, 3-year-old lactating cows were inoculated with intra-mammary infusions of H5N1. Within 24-48 hours, cows started showing signs of disease. Milk production decreased, milk changed color and consistency and dry matter intake decreased. After 14 days, neutralizing antibodies were detected and by 21 days, virus isolation was negative. Upon further examination of the mammary tissue, researchers found that parts of the tissue showed fibrosis, suggesting that there is some permanent damage to the mammary gland after infection.
Recent epidemiological data has shown that flocks in Michigan became infected with H5N1 when employees who worked at the poultry farm also worked at a nearby infected dairy farm. Based on USDA’s two pilot studies, the Michigan epidemiological study and multiple field investigations, it is still presumptive that H5N1 is being spread mechanically through contaminated raw milk. This mechanical transmission is why many agricultural officials and veterinarians are encouraging farms to increase their on-farm biosecurity. This not only includes ensuring employees remain vigilant, but also making sure delivery trucks and their drivers, sales representatives, and any visitors, thoroughly wash their boots, hands and if possible, vehicles, before moving from farm to farm. Encouraging dairy farms to work with herd veterinarians on appropriate biosecurity plans is imperative to stopping the spread of this disease.
It is important to remember that there have also been several studies showing that even at very high levels of viral load, pasteurization is still effective in eliminating the virus.
In an effort to encourage dairy farms to test and report suspicious cases, so that we can better understand the scope of this outbreak, the USDA has offered several programs to assist farmers financially. This includes paying for biosecurity plan development, testing of animals and indemnity payments. There is also a herd status program that allows routine testing in an effort to minimize or eliminate the cattle movement restrictions currently in place. The nuances of each of these programs is beyond the scope of this article, however there are several fact sheets and FAQ documents on the USDA website.
In summary, we are learning more about H5N1 in dairy cattle on a daily to weekly basis. This disease is still an active disease among dairy farms that can be devastating not only to the individual dairy, but also to neighboring farms. All of us in the agricultural industry have the responsibility to keep our food supply safe. Encourage your customers to reach out to their veterinary partners to learn what they can do to protect their own farm and help stop the spread of H5N1.