By Tom Polansek
CHICAGO (Reuters) – The U.S. Department of Agriculture said this week that cow-to-cow transmission is a factor in the spread of bird flu in dairy herds, but it does not yet know exactly how the virus is being transported.
Farmers and veterinarians are awaiting confirmation of how the virus is transmitted to better control its spread. Dairy herds in eight states tested positive last month, along with a dairy worker in Texas.
“Those of us who have worked on influenza for a long time are quick to say, ‘Yes, it moves cow to cow,'” Jim Lowe, associate dean of the University of Illinois College of Veterinary Medicine, said Friday. “You can’t explain epidemiology any other way.”
Wild migratory birds are believed to be the original source of the virus. But the USDA said its investigation into cow infections “includes some cases in which the spread of the virus was associated with movements of cattle between herds.” There is also evidence that the virus spread from dairy facilities “back to nearby poultry facilities via an unknown route,” the department said.
The USDA said cows transmit the virus in milk in high concentrations, so anything that comes into contact with unpasteurized milk can spread the disease. Respiratory transmission is not considered the main way the virus spreads in livestock, the department added.
Despite the uncertainty about transmission, the USDA has not imposed quarantines to restrict the movement of cattle around infected dairy farms, as it does chickens and turkeys around infected poultry farms. Infected livestock appear to recover, while bird flu is generally lethal to birds.
The USDA said it hopes that minimizing the movement of livestock and testing those that must be transported, along with safe and clean practices on farms, will avoid the need for regulatory restrictions.
Officials reported last month that bird flu primarily affected older cows, although additional data now indicates that younger cattle were affected, the USDA said.
(Reporting by Tom Polansek, editing by Louise Heavens)
