Infectious Diseases 2024

A group of researchers from Iowa State University reported their findings on some of the earliest cases of Highly Pathogenic Avian Influenza (HPAI) in cows and cats in the journal Emerging Infectious Diseases. The researchers identified the highly pathogenic avian influenza A(H5N1) virus in dairy cattle and cats in Kansas and Texas, United States, which reflects the continued spread of clade 2.3.4.4b viruses that entered the country in late 2021. Infected cattle exhibited nonspecific illness, accompanied by reduced feed intake and rumination, and experienced an abrupt drop in milk production. The milk from most affected cows had a thickened, creamy yellow appearance similar to colostrum. On affected farms, the incidence appeared to peak 4–6 days after the first animals were affected and then tapered off within 10–14 days; afterward, most animals were slowly returned to regular milking. Abundant virus shedding was found in milk from affected cows. The magnitude of this finding is further emphasized by the high death rate of cats on farm premises that were fed raw colostrum and milk from affected cows.
These findings suggest cross-species mammal-to-mammal transmission of the HPAI H5N1 virus and raise new concerns regarding the potential for virus spread within mammal populations. The study indicates that dairy cattle are susceptible to infection with the HPAI H5N1 virus and can shed the virus in milk, potentially transmitting infection to other mammals via unpasteurized milk. The recurring nature of global HPAI H5N1 virus outbreaks and the detection of spillover events in a broad host range are concerning and suggest increasing virus adaptation in mammals.