Epidemiology Investigation Of Duck Viral Hepatitis In Some Areas Of Shandong Province

Duck viral hepatitis （DVH） is a highly mortal and rapidly spreading disease, which iscaused by duck hepatitis virus （DHV）. The clinical symptoms are hemorrhage, necrosis andedema in disease duck liver, and most "opisthotonos" specific posture in the time of death,commonly known as the “dorsal neck disease”. The disease predominantly infects3weeksducklings, and it is one of the major diseases seriously risks to the duck industry. Thedisease can be caused by three different types of viruses, termed as type Ⅰ, Ⅱ and Ⅲofduck hepatitis virus. In order to understand the prevalence of duck virus hepatitis inShandong region, since August2010,31suspected duck viral hepatitis samples werecollected from parts of Shandong, and studied on the incidence investigation,histopathological observation, virus isolation and identification, gene cloning andsequencing analysis.Through the survey about the incidence of suspected duck viral hepatitis samples indifferent regions of Shandong, we find the development of Shandong duck industry isvigorous in recent years. Each region has a higher proportion of duck viral hepatitis samples,mainly infecting the4-week-old duckling, and larger day-old ducks can also be infected.The disease has no obvious seasonal incidence, prevalence throughout the year, mainly inautumn and winter, and it is obvious different from the higher incidence in spring. Theincidence and mortality between ducks have comparatively large differences. The incidenceof the disease is closely related to sick ducks day-old, duck feeding management andenvironmental sanitation. Especially in last few years, the prevalence of duck Flavivirusdiseases greatly promoted the occurrence and epidemic of duck virus hepatitis. Clinicalsymptoms are depressed spirit, asocial; neurological symptoms such as head tremor,paralysis, somersaults; paralytic ducks finally due to failure of death, when died, the duck isopisthotonus posture; and it is different from previous DHV samples that many sick ducksexcretion gray and mignonette loose stool, the proportion of neurologic symptoms diseaseduck is higher, and phanero-respiratory tract symptom. These symptoms may be mainlyassociated with DHV and flavivirus mixed infection. Autopsy symptom of suspectedsamples is primarily swelling of liver, pallid or yellowish, brittle. The pathogenic ducklingoften has mottling hemorrhage on the liver; There is small gray on the spleen, some necrosisis kermesinus or mottle hemorrhagic; meninges have hyperemia and hemorrhage. It isdifferent from previous DHV samples that there is hoar focal oval swelling in the middle ofileal lymphatic tissue concentration mucosa, petechial hemorrhages on the epicardium of the heart, barred hemorrhages on the of the endocardium heart, myocardium pallid andsarcoplasm soft, and These symptoms may be mainly associated with Flavivirus infection,mostly a mixture of both infections. Pathology Histological observation showed that therewas generally degeneration, necrosis and lymphocyte infiltrates on the liver, the lighthepatocytes mainly granular and vesicular degeneration, the serious hepatocytes mainlyfatty degeneration and necrosis; the pathogenic duckling often has serious hemorrhagicnecrosis on the liver; the chronic samples showed extensive hyperplasia on the bile duct ofthe liver, and there were different degrees of inflammatory cells infiltration and hemorrhage;the spleen manifested different degrees of necrosis. In some samples there were abundantlymphocytes infiltration and proliferation in the lamina propria mucosae and laminamuscularis of the middle ileal lymphatic tissue concentration mucosa, and Myocardialhemorrhage; and most disease ducks showed moderate lesions of virus encephalitis.31samples with hepatic lesions were collected as samples. And then they wererespectively carried on PCR detection of DHV-Ⅰ, astrovirus, DHV-Ⅲ and DHBV （duckhepatitis B virus）. The results indicated that:11samples were positive for DHV among the31samples, of which10samples for DHV-Ⅰ,the positive rate was35.48%;1sample waspositive for DHV-Ⅲ, the positive rate was3.23%;17samples were positive for DHBV, thepositive rate was54.84%; among the17samples,there were4samples positive for DHV-Ⅰand DHBV, the co-infection rate was12.90%. Seven isolation virus of DHV were obtainedthrough chick embryo allantoic fluid to the fifth transfer of culture. The ELD₅₀/0.2ml of the7strains detected with chick embryo were between10^-6.34～10^-7.56,10^-6.894on average.Comparied the gene sequences, there was less mutant gene of DHV, and the viralpathogenicity was little different from previously discovered virus. DHBV survey indicatedthat17samples infected DHBV among the31samples. Although the hepatitis B virus hadnon-pathogenic when the ducks infected DHBV, the high detection rate was still relativelyrare. Though DHBV can’t infect people, the causes and the resulting public health problemshould be paid more attention by people.With the rapid development of the duck industry, duck infectious diseases arebecoming more serious, new diseases have emerged, archae-diseases is still in prevalence.With the advent of new duck diseases, it is bound to break the original balance of the ducksdisease and complicate duck diseases. Thus the process of duck feeding and managementshould be strengthened, and we should pay more attention on the study of the interaction between duck diseases, execute strict immunization program, strengthen the collectiveimmunity of ducks, reduce the incidence of disease and economic losses.