9 June 2025

2 minute read

By: Chris Wright

North America

Avian Metapneumovirus (aMPV) is an enveloped RNA virus that primarily affects turkeys and chickens, causing turkey rhinotracheitis and swollen head syndrome, respectively. Since the detection of aMPV subtypes A and B for the first time in chickens and turkeys in the United States during late 2023 and 2024, the virus has spread rapidly across the country, with detections in 30 states. As of November 2024, the state of Mississippi had no confirmed cases of aMPV.

A study by Marcela Arango and colleagues at Mississippi State University, USA, established the aMPV serological status of commercial broiler breeders in Mississippi. The results of the study were presented at the 2025 International Poultry Scientific Forum.

Serum included in this study had been submitted to the Poultry Research and Diagnostic Laboratory for routine testing. Selected serum had been submitted between July and October 2024 from 25- to 50-week-old broiler breeder flocks. Seventy submissions from all six broiler integrators in Mississippi were selected for inclusion in the study, with farms selected according to their geographic distribution in the state. Ten sera per submission were randomly selected and tested.

Geometric mean titers (GMT) were allocated into three categories following previously established criteria: 57% no seroconversion, 40% equivocal or suspect and 3% seroconversion. aMPV GMTs ranged from 4 to 8,572. Suspect GMTs were detected from serum submitted during all months and from all age groups included in the study. The two seropositive flocks belonged to different companies and tested positive in the same month (August 2024). No clinical signs or significant increases in mortality or egg production drops were reported in the seropositive flocks.

These results indicate that at least two broiler breeder flocks were likely exposed to aMPV, while several others may have been exposed. Clinical signs were not reported in the seropositive flocks, suggesting that aMPV infection may sometimes be subclinical. This study highlights the importance of serologic testing for aMPV and provides evidence for the first time of aMPV seropositivity in Mississippi flocks.