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H5N1 avian influenza spilling over to cows and cats

A new report from the CDC shows that the H5N1 avian influenza virus seems to be moving from birds to domestic cattle and cats. Moreover, there also appears to be cow-to-cow transmission of the virus. This means there may be more ways to transmit the virus to humans, especially in people who consume raw milk (which is not a good idea).

Let’s look at the CDC report and determine if there is anything to these observations and whether we should be worried.

assorted color kittens H5N1
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All about H5N1 avian influenza

Avian influenza, or what everyone is now calling “bird flu,” is a type A influenza subtype designated as A(H5N1). Without getting into all the details of the naming system, the designation is based on antigens common to this influenza subtype. Another avian influenza is designated as A(H7N9), but the current outbreak appears to be the H5N1 subtype.

As the name implies, these viruses usually affect birds but can occasionally pass from birds to humans, cattle, pigs, and other animals. The H5N1 subtype arose in Asia a few years ago and has spread worldwide. It is highly pathogenic (meaning it can cause disease in humans) and has passed to humans several times.

Infected birds shed the virus through their saliva, mucous, and feces. Human infections with bird flu viruses can happen when the virus gets into a person’s eyes, nose, or mouth, or is inhaled. This can happen when the virus is in the air (in droplets or possibly dust) and a person breathes it in, or possibly when a person touches something that has the virus on it and then touches their mouth, eyes, or nose. Human infections with bird flu viruses have occurred most often after unprotected contact with infected birds or surfaces contaminated with bird flu viruses. However, some infections have been identified where direct contact with infected birds or their environment was unknown.

There are numerous cases where bird flu has been transmitted between humans, but most infections of humans are from constant contact with infected birds. Human infection with avian influenza A virus poses pandemic potential, so CDC and other public health agencies investigate every case to assess whether human-to-human transmission might have occurred. Detailed public health investigations can help determine whether person-to-person spread of an avian influenza A virus occurred.

The signs and symptoms of bird flu infections in humans can range from nothing to severe. The infections are similar to other flu infections including fever, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, fatigue, and shortness of breath.

As I have previously written, there aren’t vaccines for the H1N5 virus, but the CDC is monitoring the situation closely, as I will discuss below so that if the virus begins to infect humans regularly, they will be able to quickly respond with a vaccine.

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CDC study

In a paper published on 29 April 2024 in the CDC’s Emerging Infectious Diseases, Eric Burrough, DVM, PhD, of Iowa State University College of Veterinary Medicine in Ames, Iowa, and colleagues analyzed samples from farms in Kansas and Texas taken in mid-March 2024. Researchers from the Iowa State University Veterinary Diagnostic Laboratory received samples from dairy cattle in Texas and Kansas, along with two dead cats from a Texas dairy farm

Here are some of their key findings:

  • Cows infected with H5N1 avian influenza had mild illness characterized by a drop in milk production.
  • Cats fed raw milk from infected cows experienced severe systemic disease with high mortality.
  • The researchers reported that milk and mammary gland samples had very low cycle threshold (Ct) values for H5N1, indicating a high viral load.
  • While the mode of transmission isn’t known, cow-to-cow transmission has been suggested because cattle herds in Michigan, Idaho, and Ohio that received infected animals have also tested positive for H5N1, according to the study.
  • Among about 24 domestic cats that were fed milk from sick cows on a north Texas dairy farm, more than half became sick and died in mid-March. They had signs of systemic influenza infection, including depressed mental state, stiff body movements, ataxia, blindness, circling, and copious oculonasal discharge, the researchers reported. Neurological examination found no menace reflexes and pupillary light responses with weak blink response.

The authors wrote, “Although the exact source of the virus is unknown, migratory birds, Anseriformes (ducks, geese, and swans) and Charadriiformes (gulls and shore birds), are likely sources because the Texas panhandle region lies in the Central Flyway, and those birds are the main natural reservoir for avian influenza viruses.”


As of this time, we still haven’t seen transmission from cows or cats to humans, except in a handful of cases. This doesn’t mean it won’t happen, it’s just that it hasn’t happened as of now.

However, there are a couple of cautions here. Avoid raw milk, because it will carry the virus. Well, there are a huge number of reasons to avoid raw milk, but avoiding H5N1 should be one of them. Second, don’t give raw milk to cats, because they seem to be very susceptible to dangerous complications from contracting avian flu.

The CDC continues to monitor the situation, so there’s no reason to panic. Unless you’re a cat on a farm being fed raw milk.


Michael Simpson

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