Epidemiological Investigation Of Avian Hepatitis E In Some Areas Of Shandong Province

Avian hepatitis E virus（aHEV）can cause big liver and spleen（BLS）and hepatitissplenomegaly（HSS）in chickens.Infection of 30-72-week-old broiler breeders and laying hens causes hepatosplenomegaly,liver rupture and hemorrhage,bleeding spots in the abdomen,and occasional ovarian degeneration,resulting in a decrease in the egg production rate and an increase in the death rate of chickens.The chicken industry poses a serious threat.In recent years,avian HEV（avian HEV,aHEV）has become widespread and exhibits genetic diversity,and some new genotypes have been reported.aHEV can also be detected in some clinically healthy chickens,but this is often overlooked.In order to understand the current prevalence of avian hepatitis E in Shandong,this study collected a total of 279 clinical suspected cases in 12 regions including Tai’an,Jinan,Dezhou,Zibo,Heze and Jining from June 2020 to December 2021.After the initial diagnosis of autopsy and histopathology,the pathogenic diagnosis and genetic evolution analysis were further carried out by molecular biology methods.The results showed that most of the suspected cases had swollen and ruptured liver,hemorrhage,and enlarged spleen during autopsy.Histopathological examination revealed hepatic hemorrhage with infiltration of heterophil,lymphocytes,and macrophages,and spleen lymphopenia.The PCR test found that 55 of the279 samples were positive for aHEV,with a positive rate of 19.71%（55/279）,CIAV)and avian adenovirus（Fowl adenovirus,FAd V）mixed infection is the most common.To further understand the prevalence of aHEV in chicken flocks,this study conducted aHEV detection on 15 chicken farms in Tai’an area.We first collected 288 egg samples and288 cloacal swab samples from 12 clinically healthy laying hen farms.The PCR test found that the number of positive samples in the egg yolk was 13,with a positive rate of 4.51%（13/288）.The number of positive samples in cloacal swabs was 18,and the positive rate was 6.25%（18/288）.During the epidemiological investigation,we found an outbreak of aHEV in 1 chicken farm,where 67 laying hen cloacal swabs and 40 egg samples were randomly collected.The test found that there were 24 aHEV-positive samples from the cloacal swabs of laying hens,with a positive rate of 35.82%（24/67）,and 4 aHEV-positive samples of egg yolks,with a positive rate of 10%（4/40）.Cloacal swabs and egg yolk samples from aHEV-affected farms had higher positive rates compared with clinically healthy farms.In addition,we also sampled and tested2 large-scale egg breeder farms in Tai’an City.The results showed that aHEV was detected in chicks,dead embryos,live embryos and egg yolks,with a positive rate of 11.67%（7/60）,10%（6/60）,13.33%（8/60）and 26.67%（16/60）.The positive samples were sequenced and analyzed,and a total of 26 aHEV partial gene sequences of ORF2 were obtained,and the genetic evolution of the virus was analyzed.The results showed that except SDFC-2 and SDFC-3,the rest of the aHEV strain sequences did not belong to the current aHEV research reports.4 genotypes（genotype 1-4）,suggesting that the aHEV detected in this study may be a potential new genotype.In conclusion,this study proves that the currently prevalent aHEV in Shandong has the characteristics of genetic diversity and mixed infection with various pathogens.At the same time,there is still a certain proportion of aHEV virus-carrying rate in clinically healthy laying hens and breeder flocks,indicating that vertical transmission may be an important transmission route of the disease.The results of the study further enriched the epidemiological data of aHEV in Shandong Province,and provided a basis for scientific prevention and control of the disease.