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Since 2020, highly pathogenic avian influenza (HPAI) has posed a threat not only to wild birds, but also to poultry globally. The HPAI virus subtype H5N1 is of concern due to its ability to infect wild and domestic mammals. Last March, cats in Texas died shortly after developing serious symptoms, such as blindness, after consuming raw (unpasteurized) milk from infected cows. This case, which constitutes a first for the virus, raises new concerns.
Toward the end of 2021, the Eurasian strain of H5N1 (clade 2.3.4.4b) was detected in North America, subsequently leading to an outbreak that continues to this day. Between 2020 and early 2024, 28 cases of avian flu were recorded in humans, including 8 deaths.
On March 16, 2024, veterinarians were alerted to a syndrome occurring in cows on a farm in Texas: a “mysterious” illness accompanied by a reduction in their milk production. The milk from the most affected cows had a thick creamy consistency and was a yellowish color, similar to colostrum. The next day, cats from the same farm, having consumed raw milk from these cows, fell ill. While the cattle now had mild symptoms and appeared to recover quickly from the disease, the cats were not so lucky.
The felines quickly developed worrying symptoms impacting both their psychological state (mental confusion, social isolation, etc.) and their physical state (vomiting, blindness, etc.). 4 days later, veterinary researchers from Iowa, Texas and Kansas reported that “the cats were found dead without any apparent signs of injury and were part of a resident population of approximately 24 milk-fed domestic cats of a sick cow.
Samples were then collected during necropsy from the brain and lungs and sent for analysis to the Iowa State University Veterinary Diagnostic Laboratory. The researchers then confirmed that the cats had been infected with the H5N1 virus. They also noted “microscopic lesions consistent with a serious systemic viral infection” in the eyes and brain. Similar results had already been observed in cats experimentally infected with HPAI. On the other hand, what the researchers considered alarming was the transmission and evolution capacity of the virus detected on the Texas farm.
An unknown mode of contamination?
Transmission of HPAI generally occurs through different routes of exposure (direct contact, water, food). Among carnivores (wild and domestic), it is very likely that the latter occurs through the consumption of infected bird carcasses. This possibility cannot be ruled out with regard to infected cats in Texas. However, according to veterinarians, the most likely hypothesis for the Source of transmission is cow’s milk. Indeed, samples were also sent to the laboratory and the results of the analyzes were clear: the raw milk present on site was full of H5N1 viral particles.
“ Our results suggest interspecies mammal-to-mammal transmission of HPAI H5N1 virus and raise new concerns regarding the potential for spread of the virus within mammalian populations. “, wrote the researchers in their study document, published in the journal
Emerging Infectious Diseases.
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This presence of H5N1 in a Texas dairy herd, confirmed by the United States Department of Agriculture (USDA), marks the first transmission to cows to date. Since then, the USDA has documented infections in at least 34 herds across nine states (Texas, Kansas, Michigan, New Mexico, Idaho, Ohio, South Dakota, North Carolina and Colorado). For its part, the Food and Drug Administration (FDA) has detected genetic traces of H5N1 in approximately 20% of commercial milk samples (despite pasteurization).
“ The recurrent nature of global H5N1 outbreaks and the detection of spillover events in a wide host range are concerning and suggest increasing adaptation of the virus in mammals “, wrote the authors of the study. “ Surveillance of HPAI viruses in domestic livestock animals, including cattle, is necessary to elucidate influenza virus evolution and prevent cross-species transmission », they conclude.
