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: From July 2010 to July 2012, four farms consisting of 50 flocks of egg-laying Muscovy ducks and 10 flocks of breeding Muscovy ducks were monitored and investigated. An outbreak in Muscovy ducks, with severe symptoms of coughing and egg-drop, occurred in these flocks in Guangdong, China. The outbreak occurred in a seasonal pattern, mainly in early spring and late autumn. Only Muscovy ducks were infected, indicating that the pathogen was species-specific. We observed upper respiratory symptoms and reduction of egg production by approximately 40-85% in the sick Muscovy ducks (Figure 1A, Farm 1, Farm 2 and Farm 3), compared with that of normal Muscovy ducks (Figure 1A, Farm 4). The eggs produced by the diseased ducks were soft, thin-shelled, or cracked (data not shown). In most cases, the symptoms lasted approximately 9–12 days and disappeared rapidly. A secondary infection often occurred afterwards. Anatomical studies showed a prevalence of white or yellow discharge in the uterine (Figure 2B) and nasal tissues (data not show). Lesions and an accumulation of egg yolk were observed in the ovarian tissues (Figure 2A).