Infiltration of Bovine Herpesvirus 4 into the Hokkaido District, Japan

Abstract

Serological investigation of the bovine herpesvirus 4 (BoHV-4) was performed on sera collected from 91 farms in 9 sub-prefectural districts on the island of Hokkaido, Japan. A B11-41 strain isolated in Japan was used as the antigen in indirect fluorescent antibody tests (IFAT). A commercial kit was used for ELISA. The results of these tests showed that farms in 3 sub-prefectural districts were antibody-positive. Detailed epidemiologlcal investlgations were then performed in the Shiribeshi district, where farms positive for the BoHV-4 antibody were located. IFAT showed 5 farms to be positive on the basis of sera collected between 1998 and 1999 and 9 farms to be positive on the basis of sera collected between 2000 and 2002. Furthermore, 4 farms that had been serologically positive in 1998 remained positive in sera collected between 2002 and 2003. Three farms positive in 2002 housed cows and heifers together. On those farms, from 64.7 to 100% of animals were positive. On 2 of those farms, more than 50% of the heifers were serologically positive. On one farm positive in 2002, where cows and heifers were separatly housed. 21.9% of the animals were positive. These results in dicate that, before its first isolation in Japan, in 1999, BoHV-4 had already existed and had spread in the Shiribeshi district. Epidemiological investigations suggest that heifers may play an important role in spreading infection and that repeated infections between cows and susceptible heifers may maintain the virus in the herd.