EPIDEMIOLOGY, PATHOGENESIS, AND COUNTERMEASURES TO PREVENT AND CONTROL AVIAN METAPNEUMOVIRUS INFECTION
Location: Endemic Poultry Viral Diseases Research Unit
Title: Deletion of the M2-2 gene from avian metapneumovirus subgroup C impairs virus replication and immunogenicity in turkeys
Submitted to: Virus Genes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 16, 2011
Publication Date: June 1, 2011
Citation: Yu, Q., Estevez, C., Roth, J.P., Hu, H., Zsak, L. 2011. Deletion of the M2-2 gene from avian metapneumovirus subgroup C impairs virus replication and immunogenicity in turkeys. Virus Genes. 42:339-346.
Interpretive Summary: Avian metapneumovirus (aMPV) is an economically important pathogen of turkeys with a worldwide distribution. The genome of aMPV contains eight genes that produce viral proteins to support virus growth in a host. One of the eight genes is the second matrix (M2) gene that may produce two proteins, M2-1 and M2-2. Both proteins are thought to play a role in virus growth, but have not been experimentally defined. In the present study, we sought to investigate the role of the M2-2 protein in virus replication. By using a genetics approach, we generated a recombinant aMPV subtype C (aMPV-C) virus in which the M2-2 gene was deleted. The biological properties of this aMPV-C M2-2 knockout virus were characterized in cell culture and in turkeys. The results show that the raMPV-C M2-2 deleted mutant grew slightly slower in cell culture, but much less efficiently in turkeys than its parental virus. Inoculation of turkeys with the aMPV-C M2-2 deletion mutant failed to produce clinical disease and a protective immune response when it was used as a vaccine. These results suggest that the M2-2 protein of aMPV-C is not essential for virus growth in cell culture, but it is required for virus growth in the natural host to produce disease and stimulate an immune response. These results assist in understanding the function of the M2-2 protein of aMPV-C in virus biology, and in developing a disease control strategy.
The second matrix (M2) gene of avian metapneumovirus subgroup C (aMPV-C) virus contains two overlapping open reading frames (ORFs), encoding two putative proteins, M2-1 and M2-2. Both proteins are believed to be involved in the RNA transcription or replication process. To further characterize the function of the M2-2 protein in virus replication, the non-overlapping region of the M2-2 ORF was deleted from an infectious cDNA clone of the aMPV-C strain and a viable virus was rescued by using reverse genetics technology. Recombinant virus, raMPV-C 'M2-2, was characterized in vitro and in vivo. In Vero cells, raMPV-C 'M2-2 replicated less efficiently (10-fold reduction) than the parental virus during the first 48 hours post-infection. raMPV-C 'M2-2 induced typical cytopathic effects (CPE) that were indistinguishable from those seen with the parental virus infection. In specific-pathogen-free (SPF) turkeys, raMPV-C 'M2-2 was attenuated and caused no clinical signs of disease. Less than 20% of the inoculated birds shed detectable virus in tracheal tissue during the first 5 days post-infection, and no virus shedding was detected afterwards. Forty percent of infected birds produced a weak antibody response (<log2 6.0) at 14 days post-infection. Upon challenge with virulent aMPV-C strain, more than 80% of the raMPV-C 'M2-2-inoculated birds showed typical disease signs and virus shedding in tracheal tissue. These results suggest that the M2-2 protein of aMPV-C virus is not essential for virus replication in cell culture, but it is required for sufficient virus replication to maintain pathogenicity and immunogenicity in the natural host.