Isolation and characterization of a subtype C avian metapneumovirus circulating in Muscovy ducks in China.
Bottom Line: The S-01 strain was able to produce a typical cytopathic effect (CPE) on Vero cells and cause death in 10- to 11-day-old Muscovy duck embryos.The deduced eight main proteins (N, P, M, F, M2, SH, G and L) of the novel isolate shared higher identity with hMPV than with other aMPV (subtypes A, B and D).S-01 could bind a monoclonal antibody against the F protein of hMPV.
Subtype C avian metapneumovirus (aMPV-C), is an important pathogen that can cause egg-drop and acute respiratory diseases in poultry. To date, aMPV-C infection has not been documented in Muscovy ducks in China. Here, we isolated and characterized an aMPV-C, designated S-01, which has caused severe respiratory disease and noticeable egg drop in Muscovy duck flocks in south China since 2010. Electron microscopy showed that the isolate was an enveloped virus exhibiting multiple morphologies with a diameter of 20-500 nm. The S-01 strain was able to produce a typical cytopathic effect (CPE) on Vero cells and cause death in 10- to 11-day-old Muscovy duck embryos. In vivo infection of layer Muscovy ducks with the isolate resulted in typical clinical signs and pathological lesions similar to those seen in the original infected cases. We report the first complete genomic sequence of aMPV-C from Muscovy ducks. A phylogenetic analysis strongly suggested that the S-01 virus belongs to the aMPV-C family, sharing 92.3%-94.3% of nucleotide identity with that of aMPV-C, and was most closely related to the aMPV-C strains isolated from Muscovy ducks in France. The deduced eight main proteins (N, P, M, F, M2, SH, G and L) of the novel isolate shared higher identity with hMPV than with other aMPV (subtypes A, B and D). S-01 could bind a monoclonal antibody against the F protein of hMPV. Together, our results indicate that subtype-C aMPV has been circulating in Muscovy duck flocks in South China, and it is urgent for companies to develop new vaccines to control the spread of the virus in China.
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Mentions: To further verify aMPV as the infective agent, 42 aMPV-positive supernatants collected from clinical samples were inoculated into 11-day-old duck embryos via the yolk sac route. After the third passage, 9 embryos exhibited growth retardation (Figure 2G, embryo No. G-2, −4, −5, −6), bleeding (Figure 2G, embryo No. G-3, −4, −5, −6, −8, −9, −10), and/or death (Figure 2G, embryo No. G-2, −3, −4, −5, −6, −7, −8, −9, −10) at 5–7 days post inoculation, while the control embryos remained normal (Figure 2G, embryo No. G-1). The embryo egg yolks and allantoic fluid collected from the dead embryos were harvested, mixed and used for passing into Vero cells. CPE was observed in the cells infected with virus-containing fluids after the fourth passage at 72 h post inoculation (Figure 3B), and no CPE was observed in the mock-infected cells (Figure 3A).