USDA scientists share that bird flu in dairy cattle was spread from its origin in Texas to 12 states and 96 dairy herds by infected cows, contaminated machinery and people who unknowingly carried the virus from farm to farm on their clothes and footwear.

Two USDA reports documented the spread of bird flu in dairy herds. Cows from infected herds were moved between farms after symptoms appeared. Equipment, including cattle trailers, was shared between farms. Farms were frequently visited by veterinarians, milk haulers and contractors. Some dairy employees work on multiple farms, and some family members work at other livestock farms.

Migratory waterfowl have often been blamed for spreading the virus, but genomic sequencing indicates this was not a factory in the spread among dairy cattle.

The USDA emphasizes enhanced biosecurity