Objective The pathogen causing a viral disease with a 65% incident rate, 90% mortality, and massive skin hemorrhage on the birds at a mule duck farm in Fuzhou, Fujian in August 2020 was isolated with its pathogenic characteristics identified.
Method The heart, liver, spleen, pancreas, kidney, skin, and other tissues of the diseased ducks were collected for the pathogen detection including virus isolation and identification, gene sequencing, and histopathological examinations.
Result PCR showed positive results only on the collected tissues from the plague virus-infected ducks. Subsequent virus isolation and identification on those positive specimens were performed, and the virus code-named as FJ2020176. The UL2 gene of the strain was sequenced to show a 97.8-99.9% nucleotide homology with the virulent strain CHV, CV, and 2085. Compared to the vaccine strain VAC, the attenuated strain 1, and the attenuated strain 2, FJ2020176 had a 528bp nucleotide insertion in its UL2 gene confirming it to be a virulent strain of duck plague virus. The histopathological examination under a microscope showed the following observations in the infected ducks: necrosis and hemorrhage on the focal liver, decreased white pulp on the spleen tissue, necrotic and exfoliated lymphocytes, hemorrhage and blood stasis on the kidney, necrosis on the lymph nodes, and hemorrhage on the bursa of Fabricius, in addition to the exterior skin hemorrhage.
Conclusion The virulent FJ2020176 was isolated from the diseased ducks with massive skin hemorrhage and severe infection and mortality rates. The bleeding on the skin was deemed a significant symptom for clinical diagnosis of the duck plague cases.
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