The purpose of this study was to detect and quantify bovine viral diarrhea virus (BVDV) quasispecies in field endemic BVDV strains, and to analyze a co-relation between quantity of these quasispieces and variety of clinical sign on bovine viral diarrhea virus infections.
Forty five of BVDV isolates in Hokkaido prefecture were analyzed by the exaltation of Newcastle disease virus (END) method, the reverse plaque formation (RPF) method using vesicular stomatitis virus, and observation of cytopathic effect (CPE). As a result, these isolates investigated were divided into five groups. The first group is 10 isolates from which END phenomenon positive (E⁺) virus was only detected. The second is 25 isolates which consisted of E⁺ virus as major and END phenomenon negative (E^-) virus as minor. The third is 7 isolates in which each virus was detected with same titer. The fourth is 2 isolates which showed only E^- virus-positive. The fifth is 1 isolate which contained cp virus. In the quantitative analysis, it was shown that the ratio of E^- virus against E⁺ virus in the strain that contained each virus varied from 2 times to 435 times. These results suggest that BVDV field isolates not only consist of E⁺ virus as major virus but also contain several quantity of E^- virus as minor virus, and that E^- virus exists frequently in the field. Moreover, it is interesting that the strains with E^- virus as major are in the field, which will be a first report. On the other hand, any co-relations between quantity of E^- virus in the field strain and epidemiological dynamism such as animal age, clinical symptoms of BVD-MD, or BVDV genotype, were not found unfortunately. However, there is the possibility of exerting an impact on symptom, because every isolates couldn’t detect E^-virus have been derived from asymptomatic infected cows.