Investigation of vehicles as a potential pathway for between-farm transmission of influenza A virus in U.S. dairy herds

Highly pathogenic avian influenza H5N1 has infected US dairy cattle and spread throughout 19 different states since March 2024.While within-farm transmission is thought to occur primarily through direct contact, local between-farm spread remains unknown, and is considered multifactorial and likely driven by routine business activities involving shared personnel, vehicles, and other conveyances.This investigation evaluated the presence of influenza A virus RNA in a convenience sample of milk transport trucks and other on-farm service vehicles in H5N1 affected areas in 3 States between May 2024 and April 2025.A total of 298 samples were collected from 52 vehicles, of which 38 were milk trucks and tankers from 2 dairy cooperatives.Influenza A virus RNA was detected in 1.3% (4/298) of samples; 2 from tires on a livestock hauler and a deadstock trailer in MI, one from a milk cabinet sample from a milk tanker in MI, and one from a tanker milk sample in CA.Although a very small percentage of samples were positive, this investigation shows that H5N1 virus can be detected on vehicles servicing US dairy herds, highlighting a potential pathway for between-farm transmission.