Genetic characterization of bovine viral diarrhoea (BVD) viruses : confirmation of the presence of BVD genotype 2 in Africa

Abstract

Bovine viral diarrhoea virus (BVDV) has emerged as one of the economically important pathogens in cattle populations with a worldwide distribution causing a complex of disease syndromes. Two genotypes BVDV 1 and 2 exist and are discriminated on the basis of the sequence of the 5′ non-coding region (5 NCR) using real-time PCR. The use of the real-time PCR is more sensitive, specific, and less time consuming than a conventional PCR, and has reduced the risk of cross-contamination of samples. 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 1 blood sample) were collected from dead and living cattle with lesions or clinical signs compatible with BVDV infection. Pooled homogenates from the same animals were prepared and total RNA extracted. 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 on a LightCycler® V2.0 real-time PCR machine (Roche Diagnostics, Mannheim, Germany). 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, 1 blood sample and 11 trans-tracheal aspirates. Eighty five (82.5%) of the strains were genotype 1 and 18 (17.5%) were genotype 2. Comparing the sequencing data, genotype 1 and 2 from the field strains did not cluster with vaccine strains currently used in feedlots in South Africa. The present study revealed the presence of BVDV genotype 2 in cattle in South Africa based on the high sequence similarity between genotype 2 field strains and strain 890 from North America. The presence of genotype 2 viruses that phylogenetically belong to different clusters and coexist in feedlots is consistent with the possibility of multiple virus introductions. These results represent the first documented evidence for the presence of BVDV genotype 2 in African cattle.