Abstract:
Bovine viral diarrhoea virus (BVDV) infection is an important viral infection affecting the
cattle industry today. The prevalence of this infection in South African feedlots is unknown.
Ear notch biopsies were collected from chronic poor doers and animals that appeared
unthrifty upon entering feedlots, as well as animals entering the hospital pen with respiratory
disease for the first time. A total of 1690 samples were collected: 1074 from the former
category and 616 from the latter. A routine immunohistochemistry staining protocol showed
that 49 animals tested positive, of which 43 (4%) came from the feedlot entry group and six
(1%) from the hospitalised group. The prevalence of persistently infected cattle from this
selected, nonrandom sample entering six large South African feedlots was found to be 2.9%,
which is higher than the international rule of thumb that 0.5% of all cattle entering feedlots
are persistently infected. There was no clear correlation between persistent infection and
respiratory disease. Serum samples were also collected when possible and 10 positive cases
were found. Results from enzyme-linked immunosorbent assays for antigen and antibody
performed on these sera correlated well with those from the immunohistochemistry staining
method in six cases, but in four cases the animals tested falsely positive owing to nonspecific
staining. Immunohistochemistry staining on ear notch biopsies is thus a reliable diagnostic
method to identify persistently infected animals with BVDV, but the pathologist should be
aware of nonspecific positive staining.
