A serological study of Rift Valley Fever virus in two regions in Tanzania

Abstract: Rift Valley Fever (RVF) is a disease caused by Rift Valley Fever virus (RVFV), which is an arbovirus. An arbovirus is a virus that is transmitted by an arthropod vector, in this case a mosquito. The virus is a member of the Phlebovirus genus in the family Bunyaviridae. It was first identified in the Rift Valley in Kenya in 1930. The disease is a zoonosis but mainly affects domestic ruminants inducing massive abortions and a high mortality among young animals. RVF has a significant negative socio-economic impact during outbreaks in affected countries. Sheep, horse, cattle, goat, camel, buffalo and human can be infected by the virus, which today is endemic to sub-Saharan Africa and the Arabian peninsula. RVFV has two transmission cycles: the epidemic cycle and the enzootic cycle. During the enzootic cycle the virus circulates at a low level and there are no notable clinical signs of the disease. The epidemic cycle often reoccurs every 3-15 years and is often associated with periods of heavy rain. In Tanzania the latest outbreak was in 2006- 2007. This degree project has been performed as a Minor Field Study (MFS) investigating the seroprevalence of RVFV in serum from sheep and goats in three different areas (Mikumi, Ngorongoro and Mahenge) in two different regions of Tanzania: Arusha and Morogoro. The purpose of the study was to evaluate whether RVFV is active during inter-epidemic periods in these areas and to get a better understanding of the epidemiology of the virus. Totally 29 of 354 analysed samples were seropositive, which is an overall seroprevalence of 11.3 % in Mikumi, 1.0 % in Ngorongoro and 11.2 % in Mahenge. The majority of the seropositive sheep and goats from all the three sampling sites were younger than seven years, indicating that RVFV circulates in low levels in the Arusha and Morogoro region during the inter-epidemic period.