Bluetongue in Tanzania: A national overview

Cattle, goats and sheep represent the first, second and third largest proportions of the livestock population in Tanzania, respectively. The three animal species represent 47.2%, 34.3% and 11.7% of the national population of quadruped meat-producing animals. Diseases constitute a major constraint to livestock mortality and the improvement of animal production in Tanzania. Among the vector-borne diseases, Bluetongue (BT) has caused considerable economic loss during outbreaks. The disease is highly infectious, noncontagious and caused by viruses of the genus Orbivirus and family Reoviridae, which are transmitted primarily biologically by various species of Culicoides, notably C. pallidipennis and C. variipennis, to domestic and wild ruminants. This review focuses, first, on the qualitative analysis of available scientific knowledge on BT to improve our understanding of the status of the disease in Tanzania. Second, it aims to quantify the existing serological and molecular data to ascertain the prevalence and distribution in different regions of Tanzania. Five eligible publications and one surveillance dataset were identified, published or conducted from 1987--2022, and statistically analyzed. The results of the enzyme-linked immunosorbent assay (ELISA) revealed that the pooled seroprevalence was 87.8% (95% confidence interval (CI) 84–91) in cattle, 58.0% (95% CI: 55–62%) in goats and 62.7% (95% CI: 59–67%) in sheep. The results of real-time reverse transcription‒polymerase chain reaction (RT‒qPCR) revealed that the pooled prevalence rates were 44.4% in cattle, 50% in sheep and 34.8% in goats. Our review revealed that antibodies against bluetongue virus (BTV) are common in many domestic and wild ruminants in Tanzania, suggesting geographically wide exposure to the virus. Monitoring the seroprevalence of BTV, as well as systematic and continuous surveillance of Culicoides population species, abundance and infection rates, is encouraged to inform the prevention and control of the spread of BT.