Histopathological, Immunohistochemical and In-Situ Hybridization Findings in Suckling Rats Experimentally Infected With Akabane Genogroups Ⅰ and Ⅱ, Aino and Peaton Viruses.

Akabane, Aino and Peaton viruses are closely related arthropod-borne viruses in the genus Orthobunyavirus of the family Peribunyaviridae that can cause congenital abnormalities in cattle, sheep and goats. East Asian Akabane virus strains are subdivided into genogroups Ⅰ and Ⅱ, and the former can also cause non-suppurative encephalomyelitis in post-natal animals. Specific detection of the infecting virus in tissues is essential for accurate diagnosis. Immunohistochemistry (IHC) has been used to identify viral antigen but cannot always detect specific viruses due to potential cross-reactivity of the primary antisera. We compared in-situ hybridization (ISH), based on the use of cocktail probe sets targeted at the RNA of each virus, with IHC for the detection of the specific viruses in tissues of suckling rats inoculated intracerebrally with Akabane (KM-1 or OBE-1 strains), Aino or Peaton viruses at 3 or 7 days of age. Most inoculated rats developed severe neurological signs and histopathological brain lesions including necrosis, spongy degeneration and non-suppurative inflammation. A rabbit polyclonal antiserum immunolabelled antigen of all three viruses within the lesions, whereas ISH specifically detected RNA of each individual virus. The distribution of viral RNA was comparable to that of viral antigens, but tended to be more widespread, especially in immature nervous tissue. Viral antigen and RNA were detected in skeletal muscle and heart of the rats infected with the KM-1 strain of Akabane virus but not with any of the other viruses. This study demonstrates the value of ISH detection of these viruses in a rat model and may prove useful for clarification of the pathogenesis of post-natal arbovirus infection.