Pathology of dose dependent inocula of H5N8 avian influenza virus in experimentally infected chicken

ABSTRACT In the present study, we assessed the pathogenicity of H5N8 avian influenza viruses belongs to the clade 2.3.4.4b in chicken. Birds of three different dose groups, 10 2 , 10 4 , and 10 6 EID 50 were used in the study. No mortality was observed in 10 2 EID0 group. Percent cumulative mortality of 10 4 and 10 6 EID 50 group was 66.67 and 100 %, respectively. Varying duration of MDT of 3.2 and 2 days was observed in 10 4 and 10 6 EID 50 group, respectively. The CID 50 of virus was found to be 10 4.5 EID 50 . High no. of viral RNA copies were found both in oropharyngeal and cloacal swabs and in various organs of birds infected in 10 4 and 10 6 EID 50 group. Significant gross and histological changes and presence of viral antigen in various organs were observed in 10 4 and 10 6 EID 50 group. So, the study concludes that Indian HPAI, H5N8 isolates are highly pathogenic in nature to chicken by affecting most organs systemically. CID 50 of this H5N8 virus indicates poor adaption in chicken and it implies poor transmission possibility of this virus for host species in field condition. Though this virus is highly pathogenic in nature as that of HPAI, H5N1 viruses, absence of endothelial staining in most organ attributes variation in replication process and pathogenesis from HPAI, H5N1 viruses. Hence, further studies need to be done to elucidate the pathobiology of this virus in various bird species. Highlights H5N8 virus belong to the clade 2.3.4.4b, Indian isolate is highly pathogenic in nature as that of HPAIV, H5N1. The dose inocula, 10 2 EID 50 is noninfectious to chicken. The dose inocula, 10 4 and 10 6 EID 50 had caused significant mortality in the inoculated chicken with MDT of 2 and 3.2 days, respectively. H5N8 virus was detected with high viral titres in clocal and oral shedding and in multiple organ with the dose inocula, 10 4 and 10 6 EID 50 . 10 4 and 10 6 EID 50 of H5N8 inocula virus caused significant gross and histological changes in multiple organs and viral antigens were detected in respective organs.