Molecular investigation of bovine leukemia virus in selected wildlife in Zambia.

Abstract

Bovine Leukemia Virus (BLV) is a member of the genus Deltaretroviruses of the family Retroviridae and causes Enzootic Bovine Leukosis (EBL). The most common manifestation of EBL is persistent lymphocytosis, which is characterized by lymphocyte count above 7500/µL of blood, with about 5-10% of cases progressing to lymphosarcomas. BLV infection causes significant economic losses resulting from reduced milk production, death of infected animals, increased veterinary costs and the ineligibility to export beef, live cattle, semen and ova. Consequently, EBL is listed as a disease of importance to international trade by the World Organization for Animal Health (OIE). There are ten distinct genotypes for BLV, genotype 1-10. While epidemiological studies have shown that BLV infection is present in dairy and beef cattle in Zambia, there has been no studies to detect BLV in wildlife. In this study, 172 archived wildlife blood samples from Buffalo Buffalo (Bubalus bubalis), Impala (Aepyceros melampus) and Hartebeest (Alcelaphus buselaphus) were tested for BLV proviral DNA. By nested PCR, one pool of Impala whole blood tested positive for the presence of BLV proviral DNA. However, BLV proviral DNA was not detected in Buffalo and Hartebeest. These results represented an estimated pooled prevalence of 5.7% of the total wildlife samples and 9.1% prevalence of the total Impala samples. Phylogenetic analysis of the env gene showed that the strain detected in Impala belonged to genotype 4 and was closely related to the BLV strain that was detected in dairy cattle in Central Province of Zambia. Amino acid analysis of the partial BLV env gene protein sequence when compared to other genotype 4 viruses detected in Zambia, Africa, Russia and Poland revealed two Q to R substitutions in the second neutralizing domain and the E-epitope. For the first time, this study demonstrated that BLV is present in impala and may be maintained in Zambian wildlife species. This study suggests interspecies transmission of BLV between wildlife and cattle in the country. There is therefore need to limit interaction between cattle and wildlife especially on farms that may be keeping both to avoid disease spill over. While risk factors for BLV transmission has not been previously studied in Zambia, transmission may be facilitated by sharing of water bodies and grazing land as well as blood sucking insects such as hematophagous flies. In order to clearly understand the epidemiology of BLV in wildlife in the country, there is need to conduct further epidemiological studies including serological studies.