The U.S. Department of Agriculture has reported that transmission from cow-to-cow plays a role in the spread of avian flu within dairy herds. However, the exact mechanism of how the virus is being disseminated remains unknown.
Farmers and veterinarians have been eager to understand the transmission of the virus to enhance control measures. In the past month, avian flu has been detected in dairy herds across eight states, as well as in one dairy worker in Texas.
“Those of us that have worked with influenza for a long time were fairly quickly saying, ‘Yep it moves cow-to-cow,'” Jim Lowe, associate dean at the University of Illinois College of Veterinary Medicine, told Reuters on Friday. “You can’t explain the epidemiology any other way.”
Wild migratory birds are suspected to be the original carriers of the virus. However, the USDA’s investigations have found instances where the virus spread was linked to cattle movements between herds. Additionally, evidence suggests the virus may have moved from dairy cattle premises to nearby poultry premises via an unknown pathway.
The USDA reports that cows excrete the virus in milk at high levels, indicating that unpasteurized milk could potentially transmit the disease. Respiratory transmission is not considered a primary means of virus transmission among cattle, according to the department, however, it does seem to impact older cows, though younger cattle have been reportedly affected as well.
Despite the ongoing uncertainties about transmission routes, the USDA has chosen not to enforce quarantines limiting cattle movement around affected dairy farms, as it does for chickens and turkeys near infected poultry facilities. While infected cattle seem to recover, avian flu is typically fatal for poultry.
The USDA believes that reducing cattle movement, testing those slated for transport, and implementing stringent safety and cleaning measures on farms can avoid the necessity of imposing regulatory restrictions.
Current confirmed cases of HPAI in domestic livestock have been reported in Idaho, South Dakota, Kansas, New Mexico, Texas, Michigan, Ohio, and North Carolina.
