An Outbreak of Encephalomyelitis of Calves Infected with Akabane Virus in Kagoshima Prefecture

Abstract

A disease of calves characterized by difficulty in standing and nervous symptoms such as ataxia and hypersensitivity occurred in beef and dairy cattle in Kagoshima Prefecture from September to November 2006. Based on histopathological findings, non-suppurative encephalomyelitis was observed in 33 clinical cases. The Akabane virus was isolated not only from the brain stem of the affected calf but also from the plasma of a sentinel calf. These 2 strains (KS-2/Mo/06 and KS-1/P/06) were antigenically and genetically close to the Iriki strain, which was isolated from the calf cerebellum in 1984. A total of 32 affected calves possessed the neutralizing antibody against Akabane virus. Seroconversion of the sentinel calves was also confirmed during an outbreak of the disease. No prevalence of Akabane virus was observed in 2005 by means of the nationwide seroepidemiological investigations, suggesting that new strains belonging to the Iriki genotype were brought from overseas to Kagoshima Prefecture in the summer of 2006, and the virus caused an epizootic of encephalomyelitis in antibody-free cattle.