13 November 2024

3 minute read

By: Chris Wright

North America

Editor's note: Excerpts from a presentation by Darrell Kapczynski and colleagues, USDA-ARS, during the 2024 annual conference of the American Association of Avian Pathologists.

Avian metapneumovirus (aMPV) is the causative agent of turkey rhinotracheitis, an acute upper respiratory tract infection of turkeys, and is associated with swollen head syndrome in chickens. The disease is usually accompanied by secondary bacterial infections that can increase morbidity and mortality. aMPV infection of turkeys was first reported in the late 1970s in South Africa, and viruses were subsequently isolated in Europe, the US, Asia, as well as Central and South America.

aMPV belongs to the Metapneumovirus genus within the Pneumovirinae subfamily of the Paramyxoviridae family. It is a single-strand, nonsegmented, negative-sense RNA virus that contains eight genes. Currently only one serotype of aMPV has been described; however, nucleotide sequence analysis has identified four subtypes: A, B, C and D. Until recently only subtype C had been identified in the US.

Swab samples were obtained from turkey hens from North Carolina that were demonstrating respiratory distress and drops in egg production. The samples produced a positive reaction by quantitative real-time RT-PCR to aMPV B. Subsequently, a virus was isolated. In addition, testing of field samples from North Carolina demonstrated that the virus could first be detected in September of 2023.

Proximity to European aMPV

Excerpts of a presentation by Sumit Jangra and colleagues, Animal Disease Research and Diagnostic Laboratory, South Dakota State University, during the 2024 annual conference of the American Association of Avian Pathologists

Avian metapneumovirus (aMPV) is a highly contagious virus that inflicts significant economic losses on the turkey and broiler breeder sectors through respiratory and reproductive disorders. aMPVs are classified into four subgroups (A, B, C, and D) based on the level of genetic variations and antigenic differences. Recently, outbreaks of severe respiratory symptoms and significant decline in egg production were reported in turkey and chicken farms from different states in the US.

Tissues and swab samples were received that confirmed the presence of aMPV subtype B. Five whole genomes were assembled from turkey samples and one whole genome from chicken samples. Based on whole genome sequence analysis of these six genomes, subtype B strain from the recent outbreak is showing 98.5% nucleotide identity with pathogenic VCO3/60616 and 657/4 subtype B sequences detected in turkeys from France and Hungary, respectively.

The whole genomes of subtype B assembled from different farms are 100% identical, indicating that one type of strain is circulating in chicken and turkeys. Real-time RT-PCR kit detecting subtype A/B was used for screening samples from different farms; 119 out of 157 farms tested positive, with Ct values ranging from 16.5 to 36.7. Both breeders and commercial flocks tested positive by next generation sequencing and PCR.

This documented detection of aMPV subtype B in the US exhibited close phylogenetic proximity to European aMPV subtype B strains. These findings warrant further investigation into the emergence, potential consequences, and adaptation of this subtype within US poultry.