Abstract
Since March 2024, HPAI H5N1 virus has infected dairy cattle in the U.S., prompting concern about novel transmission routes. During an outbreak in California, HPAI H5N1 RNA was detected in an asymptomatic bull’s semen. Although infectious virus was not isolated, questions remain about semen-associated transmission risks and biosecurity practices.
Main Text
Since March 2024, detection of clade 2.3.4.4b highly pathogenic avian influenza (HPAI) H5N1 in U.S. dairy cattle has raised concerns about the virus’s ability for cross-species transmission, adaptation to mammals, and novel transmission routes, including milk (1,2). The knowledge that viruses are infectious in bovine semen and the finding of HPAI in turkey semen, has prompted questions about the potential role of HPAI transmission in bovine semen (3,4). The shedding of HPAI H5N1 in bovine semen could result in silent viral spread within herds and across geographic regions via artificial insemination (AI). While there are reports of clinical HPAI disease in female calves and pregnant animals, reports of diseased bulls in dairies or beef cattle are lacking. While many questions about the pathophysiology of HPAI H5N1 in U.S. dairy herds remain unanswered, movement of lactating cows is a recognized risk factor for interstate disease spread. This diagnostic study sought evidence of HPAI H5N1 shed via semen in natural breeding bulls on an HPAI H5N1-affected dairy farm in California.