Avian influenza virus spreads from chickens to cats
For months, the Avian Flu virus H5N1 has been spreading among cattle herds and chicken farms in the USA. A research team is now testing other livestock species living on these farms and finds that cats and raccoons have also been infected.
According to researchers, the Avian Flu virus H5N1 is likely to be transmitted from chickens to cats and raccoons. Their study provides further evidence for the transmission of viruses between animal species. Now, scientists are concerned that further mutations could make the virus more dangerous for humans. The study by the team led by Diego Diel from Cornell University in Ithaca has been published in the journal "Nature".
"This is one of the first times we have evidence for efficient and sustained transmission of the highly pathogenic Avian Flu H5N1 from one animal species to another," says Diel. The virus genomes obtained from dairy cows, birds, house cats, and a raccoon from affected farms indicate transmission between animal species, writes the team.
The risk of transmission from human to human remains low: "The sequencing of the entire virus genome showed no mutations in the virus that would lead to improved transmissibility of H5N1 in humans," says Diel. The data, however, clearly showed transmission from animal to animal, "which is concerning, as the virus can adapt in animals."
Virus transport via cow across the USA
A highly infectious variant of Avian Flu spread from Southeast Asia starting in 2005, first in wild birds and then in poultry, later also in livestock. Diel and colleagues investigated viruses and animals in nine US farms that reported 2024 cases of sick dairy cows. The infected dairy cows ate less, had nasal discharge, and produced altered feces and less milk.
Five of the farms were in Texas, two in the neighboring New Mexico, one in nearby Kansas, but one also in far-off Ohio. On March 8, 2024, 42 apparently healthy dairy cows from Texas were transported to a farm in Ohio. Five days later, illness symptoms appeared on the origin farm for cattle, twelve days later also for cows on the farm in Ohio. "These results indicate the transmission of the highly pathogenic Avian Flu H5N1 between subclinically infected cows," writes the team led by Diel, who also analyzed the viruses.
Investigations revealed that there was a smaller amount of viruses in the nasal mucus and blood of cows, but a very high amount in the milk. Researchers discovered that H5N1 viruses of genotype B3.13 could multiply in certain cells of the milk glands. This is another piece of evidence that transmission via the respiratory system is not the only way, but that transmission via milk and uterus can also occur, for example through insufficiently cleaned milking machines. The dead cats on several investigated farms were fed raw milk. The dead raccoon on a farm could have also consumed such milk.
Based on these and further findings, particularly through genetic investigations, researchers outline this sequence of events: In an unknown host animal, the genotype B3.13 developed. It was first detectable in a goose in Wyoming, a Peregrine Falcon in California, and a skunk in New Mexico at the beginning of the year 2024. Another unknown host animal, possibly a wild bird, then transmitted the virus to cattle, from which it found further hosts - besides cats and a Raccoon also Pigeons and other birds.
In the USA, the eleven cases of avian influenza in humans since April 2022 have been mild and symptomatic so far. The affected individuals worked on poultry and cattle farms and likely became infected directly from the animals. Researchers are now concerned that the virus could further adapt, potentially increasing its infectiousness and transmissibility to other species, including humans.
The study by Diel's team also found infected house cats on the affected farms, adding to concerns about the virus's potential spread to various animal species. Viren, a researcher involved in the study, stressed the importance of continual education and precautions to prevent human-to-human transmission of Bird flu, especially given the virus's ongoing mutations. In light of the findings, it's crucial for cat owners in the United States of America to be vigilant about their pets' health and potential exposure to infected birds or contaminated environments.
