Explainer: Avian flu in dairy cows warrants close attention

Glacier FarmMedia—The recent outbreak of avian influenza virus in cattle in the U.S. is one of the top animal health stories in North America. Here is some background information about the virus. However, as this is a rapidly changing situation, some information in this article may have changed by the time of publication.

An emerging disease syndrome was originally identified in dairy cows in Texas. These cows were identified by animal care workers and veterinarians as having the main clinical signs of reduced milk production and decreased feed intake.

Approximately 10 per cent of the cows seem to show clinical signs on affected farms. No deaths occurred and cows seemed to recover with supportive care within two to three weeks. However, loss of milk production was significant. These same farms reported deceased wild birds on their properties.

On March 25, avian influenza virus was confirmed as the cause of this disease in cows, by isolating the H5N1 avian influenza virus from milk samples and nasal swabs from infected cattle. This is the first reported case of avian influenza virus in cattle.

At the time of writing this article, cases have been confirmed in six states. To my knowledge, it has not been confirmed in beef cattle yet, but there is no reason to suspect the virus could not cause some level of disease there as well.

There are four major strains or serotypes of influenza viruses, A,B,C and D. This particular virus is Influenza A, which has a main reservoir host of waterfowl and shorebirds.

Some other serotypes of influenza virus already exist in cattle. Influenza D has been associated with respiratory disease in several studies, but influenza A has not previously been associated with disease in cattle.

Influenza viruses have a remarkable ability to change and adapt. Re-assortment can occur when an animal or human is infected with more than one subtype at the same time. For example, if a host is infected with H5N6 and H4N1 at the same time, the virus can reassort the surface proteins to become H5N1 subtype.

In addition to that, these viruses can also mutate rapidly. As they do, they tend to become more virulent and require a reduced infectious dose to infect animals. Mutations may also allow them to jump to a new species.

You may have heard of highly pathogenic avian influenza and low pathogenic avian influenza. This term refers to how the disease manifests itself in chickens.

Highly pathogenic avian influenza causes severe disease and death in naïve chickens and is largely controlled by depopulation of flocks that are infected with it. Birds can recover from low pathogenicity avian influenza and outbreaks are controlled by biosecurity and vaccination.

Although this is a “highly pathogenic” strain, it is not highly pathogenic in cattle. It causes relatively mild disease from which animals seem to recover with only supportive care.

Will this new strain infecting cattle make its way to Canada? We don’t know , but it is likely that migrating wild birds will bring it north with them. It might also be moved by transporting infected cattle. Provincial government veterinarians and the CFIA will be working to develop plans for surveillance.

It will be important for producers to identify unusual signs of disease in their cattle and have them examined by a veterinarian. Unfortunately, vaccines will take at least six months or more to develop so we won’t be able to rely on any protection through vaccination.

The American Association of Bovine Practitioners has published biosecurity recommendations to address this newly emerging virus. Minimizing access of wild birds to cattle and the environment might be possible in dairy operations, but it is obviously very difficult in most beef operations.

Most recommendations are basic biosecurity principles such as monitoring cattle health, managing movement and transport, quarantining any new animal introductions for 21 days, cleaning and disinfecting trucks or trailers, and limiting non-essential visitors to the farm.

Avoid feeding raw colostrum from dairy cows to calves and if you are a cow-calf producer, it is a good biosecurity practice to not buy supplemental colostrum from dairies.

H5N1 avian influenza virus can cause disease in people and if cases occur in cattle herds, ensure there are biosecurity precautions to prevent infections in people working with the cattle.

Clean clothing and footwear, hand washing and use of gloves are all basic precautions. Regular disinfection of equipment should also be done.

There is no risk of infection to people in properly cooked meat or in pasteurized milk. This is not a food safety issue and there is no evidence that eating properly cooked meat, eggs or pasteurized milk could transmit avian influenza to humans.

This is another example of an emerging disease issue that we will have to adapt to. So far, it appears relatively mild in cattle. Work with your veterinarian if you identify any unusual disease symptoms in the herd.

—John Campbell is a professor in the department of Large Animal Clinical Sciences at the University of Saskatchewan’s Western College of Veterinary Medicine.