Lack of Avian Metapneumovirus Detection of Subtypes A and B in Eggs from Virus-Positive Commercial Turkey Breeders Supports the Premise That Vertical Transmission Does Not Contribute to Virus Spread

Avian metapneumovirus (aMPV) is a globally widespread avian disease. Infection with the virus causes respiratory illness and contributes to secondary infections, resulting in increased morbidity and mortality with serious economic losses. The virus is classified into four subtypes (A-D). Historically, the United States experienced geographically limited outbreaks of subtype C in turkeys during the late 1990s, which were eventually eradicated. In 2024, cases of aMPV subtypes A and B were reported in commercial chicken and turkey flocks, marking the first time these subtypes were detected in the United States. Although outbreaks of subtypes A and B have been detected in both chickens and turkeys, turkeys appear to be more susceptible and have a higher morbidity and mortality rate. Currently, a concern for the turkey industry is the possibility of vertical transmission of the virus from hen to poult. In these studies, we confirmed the presence of aMPV in the respiratory tract of infected commercial turkeys and then examined eggs from aMPV-positive laying hens for the presence of viral RNA that might suggest vertical transmission of the virus. Eggs from seven different aMPV-positive commercial turkey flocks were harvested and tested for aMPV subtypes A and B via quantitative real-time PCR. Results demonstrate no evidence of viral RNA in any of the egg or embryo samples tested, either inside or on the shell surface. These results provide direct evidence that vertical transmission does not appear to contribute to virus dissemination in commercial turkey flocks.