US veterinarians investigating the unexplained deaths of cats on a Texas dairy farm have concluded that cows infected with bird flu can transmit the virus to other mammals through raw milk.
Although cases of domestic cats infected with avian influenza – normally transmitted by birds – are well documented, this is the first time that veterinarians have linked the disease in cats to exposure to infected raw milk.
The breakthrough followed a multistate collaboration in which veterinarians worked day and night to figure out why cats were dying or disappearing on dairy farms with reported infections of highly pathogenic avian influenza (HPAI) H5N1 in cattle.
“HPAI virus infection should be considered in dairy cattle when there is an unexpected and unexplained abrupt drop in feed intake and milk production and for cats when there is a rapid onset of neurological signs and blindness,” explained lead researcher Dr. .
Samples from cats that died on a farm in Texas were tested at the Iowa State University Veterinary Diagnostic Laboratory (ISUVDL), with similar sets of samples received from livestock located at affected dairies in Kansas. The same virus – HPAI H5N1 – was found in both species, including in raw cow’s milk that was fed to cats.
Although infected dairy cattle showed mild symptoms, more than half of the sick cats eventually died.
Cat-specific symptoms included blindness and chorioretinal lesions (a type of eye inflammation), with neurological signs and death developing rapidly.
After testing tissue and milk samples from cows and cats, researchers found microscopic lesions in both species, with the cats’ lesions being “consistent with a serious systemic viral infection,” including signs of lung, heart and eye damage.
Meanwhile, the raw milk tested was found to contain a high viral load and is believed to be the main reason why the cats became infected.
The discovery raises questions about how infectious raw milk from sick cows is and the risk of transmitting the virus it poses to other mammals on dairy farms. Additional research is needed to confirm how the virus spreads from dairy cattle to cats and other species.
“In conclusion, we have shown that dairy cattle are susceptible to HPAI H5N1 virus infection and can transmit the virus in milk and, therefore, can potentially transmit the infection to other mammals through unpasteurized milk,” the researchers said.
“The recurrent nature of global outbreaks of the HPAI H5N1 virus and the detection of rebound events across a wide range of hosts is concerning and suggests increasing adaptation to the virus in mammals. Surveillance of HPAI viruses in domestic farm animals, including cattle, is necessary to elucidate the evolution and ecology of influenza viruses and prevent interspecies transmission.”
Source:
Burrough ER, Magstadt DR, Petersen B, Timmermans SJ, Gauger PC, Zhang J, et al. Highly pathogenic avian influenza A (H5N1) clade 2.3.4.4b virus infection in domestic dairy cattle and cats, United States, 2024. Emerg Infect Dis. 2024 July [02 May 2024].
DOI: 10.3201/eid3007.240508
