Pathogenesis of low pathogenic avian influenza virus subtype H6N1 infection in chickens
Epidemiology Research Department
A study on the pathogenesis of a H6N1 low pathogenic avian influenza (LPAI) virus was carried out in specific-pathogen-free chickens by investigating the gross and microscopic lesions, viral antigen and RNA distribution in tissues, and viral shedding. SPF chickens at the age of 28 days were inoculated intranasally with the LPAI virus of subtype H6N1 (A/chicken/Taiwan/19120018/2019) and sampled on 3, 7, 10, 14 days post-inoculation (DPI). The presence of viral antigens in tissues and viral RNA loads were detected by immunohistochemistry (IHC) and quantitative real time RT-PCR (qRT-PCR), respectively. Except for a chicken dying on 8 DPI, no clinical signs were observed during the period of this study. Grossly, only the dead chicken displayed lesions of renomegaly and systemic gout. Histopathological analysis revealed that renal tubular necrosis was present in all infected chickens. IHC revealed tha the viral nucleoprotein (NP) antigen was abundantly present in the kidneys of all infected groups, while NP antigen was also found in rare epithelial cells of the bronchi on 3 dpi. Higher viral RNA loads in the kidney were detected by qRT-PCR on 3 and 7 dpi, in the larynx and rectum on 3 dpi, and in the bursa of Fabricius on 3 and 10 dpi. Oropharyngeal and cloacal viral shedding was detected starting on 1 dpi, with higher oropharyngeal vial shedding detected on 1 compared to 7 dpi and when compared to cloacal viral shedding on 3 dpi. No viral shedding was detected on 14 dpi. Finally, the present study demonstrates that the main replication site of the LPAI virus subtype H6N1 in chickens is the renal tubules.
Development of a goose hemorrhagic polyomavirus vaccine
Goose hemorrhagic nephritis is caused by the goose hemorrhagic polyomavirus and the disease mainly occurs in goslings aged 4- 10 weeks, with a mortality rate of 4-67% and younger goslings having a higher mortality rate. Infected geese typically exhibit a variety of neurological symptoms such as ataxia, head and neck tremors as well as hematochezia. The pathological conditions are kidney inflammation and hemorrhagic enteritis. Goose hemorrhagic nephritis is one of the major diseases affecting European goose populations. Although it is not listed as a notifiable disease by the World Organization for Animal Health, it is listed as a disease that requires animal quarantine in Taiwan. Clinically, the disease is not easy to distinguish from parvovirus infections in waterfowl. One of the reasons making this disease difficult to control is that the diseased geese continue shedding the virus. Currently, there are no commercial vaccines available, so effective management of the disease can only be implemented with operational controls and feeding management. We developed a goose hemorrhagic nephritis vaccine by propagating goose hemorrhagic polyomaviruses via cell culture. Vaccine safety and efficacy tests were undertaken and for goslings, the antibody titer after immunization can reach SN 1:200, as tested by virus neutralization assays.