Bird flu has plagued poultry for more than 100 years, causing the death of birds like chickens, ducks, and geese. Bird flu is caused by an influenza virus similar to what causes human flu and has 4 different variants. The most potent variant is type A, which can infect people and has the potential to cause an influenza pandemic because it is easy to transmit.
In February of 2024, a team of researchers working with the CDC heard reports of dairy cattle with unusual symptoms. These cows were not motivated to eat, had decreased milk production, and produced thick, yellow, creamy milk. The infected cows’ symptoms became most prominent in 4 to 6 days and then tapered off after 10 to 14 days. Afterward, the cows gradually returned to milking.
In March of 2024, there were similar reports of dairy cattle acting sick in the southwestern part of Kansas and the northeastern part of New Mexico. However, this time wild birds and cats were dying at a dairy farm where infected cows were identified. The scientists became concerned that this unexplained illness could spread to humans and cause another pandemic. The team set out to learn about this illness to help prepare the country to fight it.
The researchers went to a dairy farm in Texas where they collected samples of milk, blood, and tissue from 6 deceased cows that were infected by the virus and 2 deceased cats. This farm had 24 cats that were fed unpasteurized cow milk, and over 50% of them died within 4 days of the first cow having symptoms. The researchers wanted to determine whether these animals died of the same disease, which would suggest it could be transmitted between species.
By the naked eye, there were no clear indicators of irregularities on the bodies of the animals, other than lesions on the mammary glands of 2 of the cows. However, the researchers suspected there may be genetic evidence of the infection in the animals, such as viral DNA or RNA. The team tested for the presence of viral DNA or RNA using a method known as a polymerase chain reaction or PCR.
When the researchers performed PCR on the cows’ milk and tissue samples from the cats, they found signs of the Avian influenza virus. The scientists sent samples to the US Department of Agriculture National Veterinary Services Laboratory, which confirmed the virus was bird flu.
Moving forward, the researchers wanted to figure out why the cattle were not motivated to eat and why only 2 cows had lesions on their mammary glands. To do this, they analyzed the digestive systems of the 6 cows. The researchers found that the cows were not fully digesting their food and had small stomach ulcers. When the researchers looked at tissue samples from the 2 cows with lesions, they found elevated white blood cell counts. They concluded that the virus was traveling from the cows’ stomachs to their mammary glands.
Lastly, the researchers wanted to determine if cows and cats were infected with the same virus variant. The researchers used PCR to compare the viral DNA of infected cattle and cats and found that 2 important viral gene sequences, HA and NA, were nearly identical. Furthermore, they discovered that infected cows at different dairy farms in Texas had the same HA and NA sequences in both their milk and tissues. The scientists concluded that one strain of the virus was spreading rapidly between cattle across the country.
The researchers explained that transmission of the bird flu between cows and other species is clear, but the core mechanism of transmission of this virus is not. They suspected that the cows were infected when they accidentally ate the droppings of infected birds and that the cats were infected when they drank contaminated cow’s milk. However, there could be other possibilities. The researchers urged the public to avoid unpasteurized milk to protect themselves from catching the virus.
The researchers stressed that further testing and investigation is needed to determine the potential threat of bird flu. They recommended that if dairy cows are not producing milk and have a decreased appetite, they should be tested for avian influenza to prevent the virus from spreading and mutating to a more potent variant.
