Genetic characterization of bovine viral diarrhoea viruses isolated from cattle in South Africa

Abstract

Bovine viral diarrhoea virus (BVDV) has emerged as one of the economically important pathogens in cattle populations with a worldwide distribution and causing a complex of disease syndromes. It is a single-stranded RNA virus of the genus Pestivirus in the family Flaviviridae. Two genotypes (1 and 2) of BVDV exist and can be distinguished on the basis of the 5' non-coding region (5' NCR) of the genome using real-time PCR. This technique is more sensitive, specific, less time consuming and has reduced risks of cross contamination of samples compared to a conventional PCR. Limited information exists on BVDV genetic subtypes in South Africa. The aim of this study was to determine the genotypes of BVDV currently circulating in South African feedlots. A total of 279 specimens (219 tissue samples, 59 trans-tracheal aspirates and one blood sample) were collected from dead and living cattle. Pooled homogenates from the same animals were prepared and total RNA was extracted from 200 μl of the homogenates using the RNeasy Mini Kit (Qiagen) as described by the manufacturer. A screening test was performed on the pooled samples and positive pools were investigated individually. The Cador BVDV Type 1/2 RT-PCR Kit (Qiagen, Hilden, Germany) was used for the real-time PCR assay. The PCR was performed on a Lightcycler® V2 (Roche Diagnostics, Mannheim, Germany) real-time PCR machine and the amplified products were detected via fluorescent dyes. The results were read at 530 and 640 nm for BVDV 1 and 2, respectively. Bovine viral diarrhoea virus was detected in a total of 103 samples that included 91 tissue samples, one blood sample and 11 trans-tracheal aspirates. Eighty five of the strains were genotype 1 strains and 18 were genotype 2. These results represent the first documented evidence for the presence of BVDV genotype 2 in South African cattle.