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Pathogenicity of egg-type duck-origin isolate of Tembusu virus in Pekin ducklings.

ABSTRACT: BACKGROUND:Tembusu virus (TMUV) usually affects adult ducks, causing a severe drop of egg production. It has also been shown to be pathogenic in commercial Pekin ducklings below 7?weeks of age. Here, we report a TMUV-caused neurological disease in young egg-type ducklings and the pathogenicity of the egg-type duck-origin TMUV isolates in meat-type Pekin ducklings. RESULTS:The disease occurred in 25 to 40-day-old Jinding ducklings in China, and was characterized by paralysis. Gross lesions were lacking and microscopic lesions appeared chiefly in brain and spleen. Inoculation in embryonated duck eggs resulted in isolation of TMUV Y and GL. The clinical signs and microscopic lesions observed in the spontaneously infected egg-type ducks were repeated in Pekin ducklings by experimental infection. Notably, both Y and GL strains caused 100% mortality in the case of 2-day-old inoculation by intracerebral route. High mortalities (80 and 70%) also occurred following infection of the Y virus at 2?days of age by intramuscular route and at 9?days of age by intracerebral route. CONCLUSIONS:These findings demonstrate that the egg-type duck-origin TMUVs exhibit high pathogenicity in Pekin ducklings, and that the severity of the disease in ducklings is dependent on the infection route and the age of birds at the time of infection. The availability of the highly pathogenic TMUV strains provides a useful material with which to begin investigations into the molecular basis of TMUV pathogenicity in ducks.

SUBMITTER: Liang T

PROVIDER: S-EPMC6813075 | biostudies-literature | 2019 Oct

REPOSITORIES: biostudies-literature

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Pathogenicity of egg-type duck-origin isolate of Tembusu virus in Pekin ducklings.

Liang Te T Liu Xiaoxiao X Qu Shenghua S Lv Junfeng J Yang Lixin L Zhang Dabing D

BMC veterinary research 20191024 1

<h4>Background</h4>Tembusu virus (TMUV) usually affects adult ducks, causing a severe drop of egg production. It has also been shown to be pathogenic in commercial Pekin ducklings below 7 weeks of age. Here, we report a TMUV-caused neurological disease in young egg-type ducklings and the pathogenicity of the egg-type duck-origin TMUV isolates in meat-type Pekin ducklings.<h4>Results</h4>The disease occurred in 25 to 40-day-old Jinding ducklings in China, and was characterized by paralysis. Gross ...[more]

PMID: 31651323

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Project description:Duck hepatitis virus (DHV) has always been considered one of the threats endangering duck farming in Egypt since the 1960s. In the current study, suspected DHV samples (n = 30) were obtained from commercial Pekin, Mulard (hybrid), and Muscovy duck farms and backyards in Beheira, Alexandria, Gharbia, Kafr El-Sheikh, and Giza provinces between 2012 and 2017. Diseased 3-21-day-old ducklings showed a clinical history of high mortality rates and nervous signs. Samples were screened by RT-PCR targeting the 5'UTR region and VP1 gene. The PCR-confirmed samples (n = 7) were isolated via allantoic route inoculation onto 9-day-old specific-pathogen-free embryonated chicken eggs. Embryos showed stunting, subcutaneous hemorrhages, and liver necrotic greenish-yellow foci. Duck hepatitis A virus-1 (DHAV-1) isolates were genetically analyzed in comparison to other field and vaccine strains. Phylogenetic analyses of the full-length VP1 gene sequences revealed that the obtained DHAV-1 field isolates clustered into genetic group 4 alongside other Egyptian strains isolated during the same period (95.9-99.72% similarity). Amino acid substitutions in the carboxyl-terminal of VP1 (I180T, G184E, D193N, and M213I) were identified in two strains. Also, deletion mutation at I189 was detected in three DHAV-1 strains. Additionally, the two amino acid residues E205 and N235 were common among the isolated strains and other virulent DHAV-1 strains. Two DHAV-1 isolates originated from Pekin source were selected for conducting the comparative pathogenicity testing based on detected point mutations at C-terminus of VP1. We evaluated the pathogenicity of these isolates by investigating clinical signs, mortality rates, and gross pathological and microscopic lesions. The study revealed that experimentally infected Pekin and Muscovy ducklings showed similar clinical signs including squatting down, lateral recumbency, and spasmodic kicking. Muscovy showed milder pathological changes in the liver compared to Pekin ducklings. Histopathological findings supported the gross pathological lesions detected in both breeds. In conclusion, these data provide updated information on the genetic diversity and pathotyping of Egyptian DHAV-1 strains. To the best of our knowledge, this is the first report of comparative pathogenicity of recent DHAV-1 strains in Pekin and Muscovy ducklings in Egypt and the Middle East region.

Project description:BackgroundAlthough several studies have revealed that the sensitivity of ducklings to duck Tembusu virus (DTMUV) was related to age, however, DTMUV was originally isolated from egg-laying ducks, and the ovary was the target organ of this virus. Cherry Valley breeding ducks aged 15- and 55-week-old (they are reserve breeding ducks and the normal egg-laying breeding ducks, respectively) were infected with DTMUV, using intramuscular injection, to study the effect of age-related difference on the pathogenicity of DTMUV in breeding ducks.ResultsExaminations of clinical symptoms, gross and microscopic lesions, viral loads, cytokines and serum neutralizing antibodies were performed. Results showed that obvious clinical symptoms, such as depression, ruffled feathers, ataxia and egg-laying drop were observed in the 55-week-old laying ducks, with five ducks dying at 5-7 days post infection (dpi). The 15-week-old ducks showed slight symptoms during infection. Gross lesions were severe and characterized by the congestion, hemorrhage and swelling of some organs in the 55-week-old ducks, including the hemorrhage of endocardium, hepatomegaly, splenomegaly, oviduct hemorrhage, hyperemia and deformation of the ovary. Mild endocardial hemorrhage and hepatosplenomegaly were observed in the 15-week-old ducks. Similarly, there was a significant difference in microscopic lesions between the two groups. The older ducks displayed severe microscopic lesions, specifically in the hemorrhage, interstitial inflammatory cell infiltration of the endocardium, typical viral encephalitis and hemorrhage in the ovary. But on the whole, the 15-week-old ducks showed milder lesions. Viral loads in tissues of the older group were significantly higher than those of the younger group. The levels of interferon (IFN)-γ, interleukin (IL)-2 and neutralizing antibody in the 15-week-old ducks were higher than in the 55-week-old ducks at the early stage of the DTMUV infection, suggesting the immune response in the younger ducks to DTMUV was stronger than in the older ducks.ConclusionsThese results demonstrated that age-related differences in susceptibility to DTMUV in breeding ducks was significant, with 55-week-old egg-laying ducks being more susceptible to DTMUV than 15-week-old reserve breeding ducks.

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Pathogenicity of egg-type duck-origin isolate of Tembusu virus in Pekin ducklings.

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Pathogenicity of egg-type duck-origin isolate of Tembusu virus in Pekin ducklings.

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