Epidemiological survey on bovine viral diarrhea virus infection in dairy cattle in Nagasaki Prefecture

Abstract

Neutralizing antibodies to bovine viral diarrhea virus (BVDV) type 1 and 2 strains were measured on 1,849 serum samples collected at 50 dairy farms from 2007 to 2011 in order to understand the BVDV infection status in dairy cattle in Nagasaki Prefecture. As a result, the central, north and south areas of the prefecture as well as the Goto area showed high positive rates for type 1, while the type 2 infection rate was low in the Goto area (4.2%) but high in the other three areas. Positive infection rates and antibody titers for type 1 and 2 were higher in the cattle introduced from other prefectures compared to home-produced cattle. Moreover, the antibody titers in home-produced cattle raised with introduced ones increased in proportion to the rates of cattle introduced from other prefectures. In addition, when 994 serum samples with antibody titers less than 1:2 were used for genetic testing to detect persistently infected (PI) animals, the type 2 gene was detected from one sample. This cow was suspected of being PI, but infection was not confirmed because of culling. The geometric mean titer for type 2 (202.4) was significantly higher than that for type 1 (28.5) in cattle raised in the same barn. From these results, it was confirmed that BVDV type 1 was widely distributed in the prefecture and that type 2 was also prevalent except in the Goto area. The infection risk for BVDV was likely higher in the farms raising cattle from other prefectures. In addition, the cow suspected of being PI was a possible source of type 2 infection in the farm. It was concluded that isolation and physical examination of introduced cattle, vaccination for both types and aggressive pathological confirmation of suspected PI cattle are important for prevention and reduction of the prevalence of BVDV infections.