Pathobiology of aMPV/CO/97 and the role of wild birds in the ecology of avian metapneumovirus
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Avian metapneumoviruses (aMPV) cause upper respiratory disease, primarily in turkeys. aMPV belongs to the family Paramyxoviridae, subfamily Pneumovirinae, and genus Metapneumovirus. aMPVs have been identified among poultry in Europe, Asia, Africa, and South America for some time. Since first identified in Colorado in 1997, aMPV subtype C has been a recurring problem in Minnesota turkey flocks. The emergence of this new aMPV, has lead to a need for greater understanding of basic aMPV pathology and ecology. These studies assessed aMPV/CO/97’s ability to cause disease in vivo and in vitro, as well as determined the role wild birds in virus dissemination. The inoculation of turkeys or ducks with aMPV/CO/97 resulted in little to no clinical disease. However, the inoculation of turkeys with aMPV/CO/97 three days prior to Newcastle disease virus (NDV) challenge resulted in the manifestation of clinical signs similar to what has been reported in the field. These findings suggest routine use of live NDV vaccine in aMPV endemic areas may exacerbate disease. In vitro, cell surface proteins involved in viral binding were examined by treating cells or virus with various compounds and measuring their effect using flow cytometry. Heparin, heparan sulfate, heparinase I and III were able to reduce aMPV binding to Vero cells, indicating a role for heparan sulfate in aMPV binding. In addition, treatment of cells or virus with anti-CX3CR1, anti-fractalkine, or recombinant human fractalkine, resulted in reduced binding, indicating CX3CR1 is also important for virus attachment. The final aspect of aMPV pathobiology examined was the ability of wild birds to serve as a reservoir. Wild bird serum samples were screened for the presence of aMPV antibodies and oral swabs were assayed for the presence of aMPV. A blocking enzyme linked immunosorbent assay (bELISA) was developed for testing the wild bird serum samples. Fifteen species of wild birds were examined, and five species had antibodies to aMPV as detected by the bELISA. These species included, American coot, American crow, Canada goose, cattle egret, and pigeon. aMPV was detected in oral swabs collected from coots and geese using RT-PCR with primers specific to the matrix gene.