Natural co-infection of fowl adenovirus type E-8b and avian hepatitis E virus in parental layer breeders in Hebei,China

Dear Editor, Fowl adenovirus(FAdV)and avian hepatitis E virus(aHEV)are the most important causative agents of hepatic injury,representing one of the greatest health concerns in layer chicken flocks(LCFs)in China and causes substantial economic losses.FAdVs are non-enveloped,double-stranded DNA viruses containing a genome of 43-45 kb in size and belong to the genus Aviadenovirus in the family of Adenovir-idae(Hess,2000).Based on restriction enzyme digestion patterns and serum cross-neutralization tests,FAdV is currently clustered into five species(FAdV-A-FAdV-E)with 12 serotypes(FAdV-1 to-7,FAdV-8a,FAdV-8b,and FAdV-9 to-11).Different serotypes of FAdVs cause different clinical symptoms in poultry flocks.FAdV-1 can induce gizzard erosion in chickens,whereas inclusion body hepatitis(IBH)in chickens is often associated with FAdV-2,-8a,-8b,and-11.FAdV-4 causes hydropericardium hepatitis syndrome and IBH in chickens,and its infections have caused severe economic losses in the global poultry industry(Ye et al.,2016).Avian hepatitis E virus(aHEV)is a major causative agent of big liver and spleen disease(BLS),hepatitis splenomegaly syndrome,and hepatic rupture hemorrhage syndrome(HRHS)in chickens(Sun et al.,2019).Currently,aHEV infection is widespread in chicken flocks in China(Su et al.,2018).Clinical signs of these diseases include increased mortality(l％-5％),decreased egg production(10％-40％),abdominal blood accumulation,liver hemor-rhage,and enlarged livers and spleens in broiler breeder and laying hens(Hsu and Tsai,2014).Avian HEV is a single-stranded pos-itive-sense RNA virus with a genome of approximately 6.6 kb in length,consisting of 3 open reading frames(ORFs).ORF2 encodes the capsid protein which contains the major antigenic epitopes of virus that has been proved to be closely associated with the induction of viral infection and immune responses in host cells.