New cases of mammal-to-mammal transmission: several cats died from avian influenza after drinking unpasteurized milk

On March 16, cows on a dairy farm in Texas began showing symptoms of a mysterious illness now known as H5N1 avian influenza. Her symptoms were unremarkable, but her milk supply dropped dramatically and became thick and creamy yellow. The next day, the farm cats, who had eaten some of the raw (unpasteurized) milk from the sick cows, also became ill. Although the cows mostly recovered, the cats were not so lucky. They developed depressive mental states, rigid body movements, loss of coordination, walking in circles, excessive discharge from the eyes and nose, and blindness.. By March 20, more than half of the 24 cats on the farm had died from the flu.

H5N1 in various organs

In a study published yesterday in the journal New infectious diseasesresearchers from Iowa, Texas and Kansas found that cats They had H5N1 not only in their lungs, but also in their brain, heart and eyes.. The results are similar to those observed in cats that were experimentally infected with the H5N1 virus, also known as highly pathogenic avian influenza virus (HPAI). But on a Texas dairy farm, they present an ominous warning about the potential for transmission of this dangerous and evolving virus.

The study authors concluded that contaminated milk was the most likely source of fatal infections. Although It cannot be completely ruled out that the cats became ill from eating infected wild birds., the milk they drank from sick cows was full of virus particles, and genetic data shows an almost exact match between cow milk, their milk, and cat milk. “Our results therefore suggest interspecies transmission of HPAI H5N1 virus from mammals to mammals and raise new concerns about the potential for spread of the virus among mammalian populations,” wrote the authors, veterinary researchers from Iowa, Texas and Kansas.

The H5N1 virus adapts

Early data from a farm outbreak in Texas suggests the virus is becoming increasingly transmissible to mammals, and data from other places suggests the virus is spreading widely among its new host. On March 25, the United States Department of Agriculture (USDA) confirmed the presence of H5N1 in a dairy herd in Texas, marking the first case of H5N1 transmission in cows. Since then, the USDA has documented infections in at least 34 herds in nine states: Texas, Kansas, Michigan, New Mexico, Idaho, Ohio, South Dakota, North Carolina and Colorado.

Meanwhile, the Food and Drug Administration (FDA) found genetic traces of H5N1 in about 20% of commercial milk samples. While commercial milk is still considered safe (pasteurization is expected to kill the virus, and early testing by the FDA and other federal scientists supports this expectation), the discovery suggests the virus may be spreading even more widely among milk-producing cows.

Cows are just the latest addition to H5N1’s surprisingly wide range of hosts. Amid a global outbreak in recent years that has devastated wild bird populations and poultry farms, researchers have documented unexpected and often deadly outbreaks among mammals. As of 2022, the USDA has detected H5N1 in more than 200 mammals, from big cats in zoos to seals, pumas, raccoons, skunks, squirrels, polar bears, black bears, foxes and bottlenose dolphins.