Distribution and genetic variability of avian hepatitis E virus on poultry farms in ex-USSR

Russian commercial poultry industry is tightly tied to international trade. To date, avian hepatitis E virus (aHEV) has been isolated in Australia, US, Spain, Hungary, etc., being a serious threat to commercial poultry. In hens, aHEV affects liver and immune system, namely spleen and thymus, disrupting homeostasis and hematological parameters. In Russia, aHEV genetic identification was first reported in 2009, but the current epizootic situation in poultry remains to be unknown. In this paper we report the results of genetic analysis of 415 liver samples from hens and broiler chicks aged 4-56 weeks. The samples were obtained from 68 commercial farms in 36 regions of the Russian Federation and 4 commercial farms from Belarus, Kazakhstan and Ukraine during 2009 to 2012. A total of 14 isolates were detected and sequenced. Isolates of aHEV were detected in both clinically healthy and affected chickens. No agents causing similar clinical signs, i.e. leucosis virus, Marek’s disease virus and adenovirus, were identified. In Russia, aHEV was isolated in Amurskaya, Vologodskaya, Ivanovskaya, Kaluzhskaya, Moskovskaya, Samarskaya, Saratovskaya provinces, and also in the Republic of Mari El. Ross 308 hens showed highest PCR-positive rates (8 of 14 isolates). According to RT-PCR analysis of capsid protein gene (ORF2), aHEV18198, aHEV19555, aHEV16211, aHEV18479 and aHEV18481 of 14 Russian isolates fall within European genotype 3. The aHEV16211, aHEV18479, aHEV18481 isolates are related to Chinese (China-09-G57), US (NY449, CA697A) and European (06-4582) isolates, and aHEV18198 and aHEV19555 are related to those from Australia and USA (Guelph01, CA518.3). Of 14 aHEV isolates studied, 7 samples formed a distinct genetic group. Two more isolates, aHEV18381 and aHEV18505, groups outside the three genotypes described. Overall, the pool of HEV isolates identified in Russian chicken flocks consists of isolates belonging to European genotype 3 and isolates not yet assigned to a specific genotype. The analysis of genetic variability of aHEVs isolates from different countries strongly suggests that the current classification into genotypes by geographical origin should be revised.