Abstract:
Malignant catarrhal fever (MCF) is a mostly fatal lymphoproliferative disease in cattle, pigs, farmed deer, bison and a range of wild ungulates in zoos and game parks. The disease in domestic cattle is caused by either alcelaphine herpesvirus type 1 (AlHV–1) or ovine herpesvirus type 2 (OvHV–2). Both are members of the subfamily Gammaherpesvirinae. The major reservoir host of AlHV–1 is the blue wildebeest (Connochaetes taurinus), but it is generally accepted that the black wildebeest (Connochaetes gnou) is also a reservoir host. Sheep is the reservoir host for OvHV–2. These viruses are non-pathogenic in their natural hosts. No viral studies in the black wildebeest have been reported and as the carrier status of black wildebeest has not been documented, samples from 304 black wildebeest and 51 of their foetuses were collected for this purpose. Blood samples, including serum and blood collected in EDTA-coated collection tubes; cornea and spleen samples were collected from culled black wildebeest. Cornea and spleen samples were collected from foetuses during the culling operations. Blood samples, as above, were also collected from live animals during the capture of such animals. Tissue and EDTA-blood samples were tested by means of conventional and real-time polymerase chain reaction (PCR) assays for detection of a gammaherpesvirus similar or related to AlHV–1. Conventional PCR failed to produce any consistent results. Real-time PCR successfully amplified a region on the gene that codes for a transactivator protein, open reading frame (ORF) 50. Melting curves were generated to determine which samples were positive for a gammaherpesvirus. Only 15.8% of the animals tested positive with the real-time PCR assay. Ninety percent (90%) of the foetuses tested positive and suggests that, unlike sheep lambs, the virus is mainly transmitted in utero and soon after birth. Virus isolated from a black wildebeest calf of one week of age, was confirmed by electron microscopy and sequence analysis to be a gammaherpesvirus related to AlHV–1 and used as a positive control for the real-time PCR assays. Serum samples were tested by a direct competitive inhibition enzyme-linked immunosorbent assay (CI-ELISA) for group specific malignant catarrhal fever virus antibody. All the serum samples that were tested of culled and live animals, tested positive with the CI-ELISA. This indicates a persistent infection and a carrier status.
