Objective Pathogen causing the hydrosalpinx fluid syndrome (HFS) with a declined egg-laying in breeding and egg-laying ducks was investigated for the disease control.
Method Nucleic acid amplification, pathogen isolation and identification, and artificial infection on ducks were carried out on tissue samples collected from the live or dead Sheldrake Ducks, Cherry Valley Ducks, and Muscovy Ducks that were found infected by HFS at farms in Fujian, Guangdong, Jiangxi, Zhejiang, Anhui, and Guangxi autonomous region. The disease symptoms included chylous hydrosalpinx fluids and hemorrhagic, edematous, and thickened mucosa, in addition to a declined egg-laying on the ducks.
Result No bacteria were detected in the hydrosalpinx fluid. In the clinical specimens, RT-PCR tested positive on avian metapneumovirus subgroup C (aMPV/C) but no other commonly known viruses that cause a declined egg-laying in ducks. Subsequently, the duck embryos inoculated with the viral infected samples were aMPV/C-positive and showed slight embryonic edema and bleeding on the embryo surface and liver. The virus isolation rate on the F5 embryo fluid by RT-PCR was 72.2%. The nucleotide sequences of the isolated FJ2375, GD2381, FJ2228, and JX2126 had a homology of 96.1% with the earliest reported aMPV/C-infected Muscovy duck/1999/99178/France, those of 67.8-68.7%, 66.1-66.8%, and 71.4% with aMPV/A, B, and D, respectively, and that of 67.7-68.3% with the human MPV. The sequences were more closely related to aMPV/C than the others in genetic evolution. Furthermore, the virus was successfully recovered from the artificially infected ducks that exhibited similar HFS symptoms observed in naturally diseased birds.
Conclusion The pathogenic virus that caused HFS in ducks was identified as aMPV/C. It paved the way for the development of means to accurately diagnose and effectively prevent and control the disease.
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