Bovine Influenza

H5N1 Influenza A - Associated Disease in Dairy Cattle

Updated: April 18, 2024

Dairy cattle in Texas and Kansas recently tested positive for highly pathogenic avian influenza (HPAI) H5N1; affected herds in several additional states have also recently been confirmed. The predominant clinical signs in affected cattle include a severe sudden decrease in milk production and feed intake, thickened yellow colostrum-like milk consistency, and fever. Affected herds have reported 10-15% of cattle affected within a short timeframe with older cows in mid-to-late lactation predominantly affected; no mortality has been confirmed due to this virus in dairy cattle. Affected cattle generally recover within 10-14 days and regain some/most of the loss of milk production. Increased numbers of dead birds and neurologic disease (ataxia, blindness) in cats has also been reported on several affected sites.

The Iowa State University Veterinary Diagnostic Laboratory has been heavily involved in this multi-state diagnostic investigation. The virus is readily detected in individual milk samples from acutely affected lactating cows via Influenza A (IAV) PCR testing; non-negative test results are then subtyped through additional PCR testing and forwarded to the NVSL for confirmation. The Influenza A NP ELISA (IAV NP ELISA) has shown excellent utility in identifying seroconversion of infected cattle. This is a rapidly evolving situation; information regarding the duration of viral presence in milk and signs of clinical disease in non-lactating cattle (calves, heifers, etc.) will be shared as it becomes available.