IPSF: Avian metapneumovirus outbreaks
Since 2023, aMPV subtypes A and B have spread across the USA
8 June 2026
3 minute read
By: [Excerpts of presentations at the 2026 International Poultry Scientific Forum]
Pankaj P. Gaonkar and colleagues at Auburn University and the Alabama State Diagnostic Laboratory System emphasized that avian metapneumovirus (aMPV) causes highly contagious upper respiratory and occasionally reproductive infections in poultry. It has recently emerged in the United States: type A in 2023 and type B in 2024. It can lead to increased morbidity and mortality in commercial flocks, resulting in significant economic losses.
This study summarizes diagnostic findings from commercial poultry submissions to the Alabama Veterinary Diagnostic Laboratory System (AVDLS) between January and October 2025. A total of 511 oropharyngeal, tracheal or nasal swabs from 221 commercial broiler breeder and broiler cases submitted at AVDLS for necropsy were tested for aMPV-A and B, and occasionally -C by PCR. Overall, 30.77% cases (68/221; 30 breeders, 38 broilers) were aMPV positive. Serotype A was detected in 33.96% (54/159) of samples, serotype B in 5.85% (11/188), and both in 0.86% (3/347) of the samples. There was no detection of serotype C. The age of affected breeder flocks ranged from 168-420 days, and broilers from 34-53 days.
Flock histories provided with necropsy submission included high mortality, swollen heads, and lameness. Gross lesions included swollen head, fibrinous and/or caseous exudates in the nares, skull, lung, heart, liver, and joints. Histologically, fibrinoheterophilic, caseous-granulomatous, and necrotizing lesions with intralesional bacteria were observed in these tissues. Lymphocytic meningitis, encephalitis, and tracheitis were also observed.
The major bacterial pathogens isolated were Escherichia coli (47), Pasteurella multocida (3), and Staphylococcus spp. (14). Viral codetections included infectious bronchitis virus (38), avian paramyxovirus and vaccinal infectious laryngotracheitis virus. ELISA- aMPV (A, B, C) on 3138 sera from 90 broiler breeder farms and 4 broiler farms showed 86.63% (2690/3105) of breeders and 78.79% (26/33) of broilers were positive for aMPV antibodies.
Among 20 farms tested by ELISA and PCR, 50% were positive only by ELISA, and 50% were positive by both assays. These results highlight the ongoing presence of aMPV in Alabama commercial poultry and underscore the need for continued diagnostic surveillance through both PCR and ELISA to better understand and mitigate its impact.
aMPV secondary bacterial infections
Since late 2023, aMPV subtypes A and B have quickly spread across most of the United States, predominantly affecting the eastern states with negative impacts on bird health and productivity. Several authors have reported high bacterial diversity and the isolation of bacteria from uncommon sites in infections occurring secondary to aMPV infection.
A study by Autumn Gregg and colleagues at Mississippi State University and the Mississippi Veterinary Research and Diagnostic Laboratory aimed to analyze the diversity of secondary bacterial infections identified in 68 aMPV cases submitted to the Mississippi State University’s Poultry Research and Diagnostic Laboratory over the eight-month period following the first detection of aMPV subtype A in Mississippi in late February 2025.
Secondary bacterial coinfections were identified in 58 out of 68 aMPV cases. In most cases (42), Escherichia coli was the predominant secondary bacterial infection associated with aMPV. Enterococcus cecorum, Pasteurella multocida, Staphylococcus aureus, Staphylococcus agnetis, and Staphylococcus chromogenes were isolated as the only aMPV bacterial coinfections in 12 cases. There were 177 individual isolations from various sampling sites.
E. coli accounted for approximately 65.5% (116) of total bacterial isolations, commonly from the liver, heart, brain, and bone marrow. The second most common agent identified was E. cecorum (15), predominantly from the heart, spleen, and free thoracic vertebrae. Other bacteria isolated from these cases included Gallibacterium anatis (8), S. aureus (12), S. agnetis (11), S. chromogenes (3), Salmonella spp. (7), and Pasteurella multocida (12).
Among 23 accessions with neurological signs, bacterial isolates of suspected or potential significance were recovered from all but two cases. The results of this study provide an overview of the range of bacterial coinfections that could occur in broiler breeders and broilers infected with aMPV, as well as the role of secondary bacterial infections in exacerbating disease severity during natural field outbreaks.
