|Njenga, M - University Of Minnesota|
Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2005
Publication Date: 12/1/2005
Citation: Bennett, R.S., Larue, R., Shaw, D., Yu, Q., Halvorson, D.A., Njenga, M.K. 2005. A wild goose avian metapneumovirus containing a large attachment glycoprotein is avirulent but immunoprotective in domestic turkeys. Journal of Virology. 79(23):14834-14842.
Interpretive Summary: Avian metapneumoviruses (AMPV) cause an upper respiratory tract disease of turkeys, and associate with swollen head syndrome of chickens, resulting in a significant economic loss for the poultry industry. Based on the antigenic and sequence variations of the attachment glycoprotein (G) of the virus, four subgroups of aMPV, A, B, C, and D, have been classified. The subtypes A and B of aMPV widely spread in Europe, Middle East and Asia, whereas the subtype C virus mainly circulate among commercial turkey flocks in Minnesota and the neighboring states of the U.S.A. To study the molecular biology and epidemiology of the virus and to develop a vaccine against the disease, we studied four strains of aMPV that were recently isolated from wild Canada geese in the United States. Genomic sequence analyses of these goose-isolates revealed that they belonged to the subtype C virus, but they contained a much larger G gene than any pneumovirus and metapneumovirus. The goose aMPV can grow in the upper respiratory tract of domestic turkeys, but with no signs of disease. We vaccinated day-old or two-week old turkeys with the live goose aMPV, and then inoculated the birds with a virulent strain of aMPV. The challenged birds showed mild or no clinical signs of the upper respiratory disease, suggesting that the mutant virus may be a good vaccine candidate against aMPV outbreaks in commercial turkeys.
Technical Abstract: The genomic structure and composition of an Avian metapnuemovirus (aMPV) recently isolated from wild Canada geese (goose 15a/01) in the United States, together with its replication, virulence, and immunogenicity in domestic turkeys were investigated. Sizes of seven of the eight genes, sequence identity, and genome organization of goose aMPV were similar to turkey aMPV subtype C (aMPV/C) strains, indicating it belonged to the subtype. However, the goose virus contained the largest attachment G gene of any pneumovirus and metapneumovirus, with the predicted G protein of 585 amino acids (aa), more than twice the sizes of G proteins from other subtype C viruses and Human metapneumovirus, and more than 170 aa larger than G proteins from the other aMPV subtypes (subtype A, B, and D). The large G gene resulted from a 1015 nucleotides insertion at 18 nt upstream of the termination signal of the turkey aMPV/C G gene. Three other aMPV isolates from Canada geese had similarly large G genes, whereas analysis of recent aMPV strains circulating in U.S. turkeys did not indicate presence of the goose virus-like strain. In vitro the goose virus replicated to levels (2 - 5 x 105 TCID50) comparable to those produced by turkey aMPV/C strains. More importantly, the virus replicated efficiently in the upper respiratory tract of domestic turkeys, but with no clinical signs in both day-old and two- weeks old turkeys. The virus was also horizontally transmitted to naïve birds and turkey infections with goose 15a/01 induced production of aMPV-specific antibodies. Challenging day-old or two-week old turkeys vaccinated with live goose aMPV resulted in lower clinical scores in 33% of the birds, whereas the rest of the birds had no detectable clinical signs of the upper respiratory disease, suggesting that the mutant virus may be a safe and effective vaccine against aMPV outbreaks in commercial turkeys.