Seroprevalence of Rift Valley fever in sheep and goats in Zambezia, Mozambique and preparations for a metagenomic study of arboviruses in ticks

Abstract: The virus-mediated disease Rift Valley fever (RVF) was discovered during an outbreak in Kenya in the 1930s. Since then it has spread to most parts of Sub-Saharan Africa, and in the last decades several outbreaks have caused economic and health issues in Africa, Yemen and Saudi-Arabia. The disease mainly affects domestic livestock, causing abortions, but is also a zoonosis. To be able to control the spread of the disease it is important with surveillance for better knowledge about the distribution and virus circulation even in inter-epidemic/epizootic periods. The human population is growing, and people and their livestock constantly move closer to areas with wild animals which act as reservoirs for different viruses. Also, humans and their animals often get within reach for arthropod vectors, hosting or carrying viruses. Taken together, this increases the risk for new emerging infectious diseases. This study consists of two parts. One is a seroprevalence study of RVF in sheep and goats in Zambezia, Mozambique. The other is a metagenomic study that aims to search for tick and mosquito borne viruses, including RVFV, in the same area. The RVF-study was a cross-sectional survey in cooperation with the University of Eduardo Mondlane (UEM), Maputo, Mozambique. Between the 25th of September and 2nd of October in 2013, blood samples were collected from sheep and goats in 8 different farms. Blood-sera from 187 goats and 181 sheep were analysed at the veterinary faculty of UEM with a commercially available ID-vet competition ELISA-kit. On the same field trip ticks were collected from sheep, goats and cattle. The metagenomic study was however only initiated during the time of this project and the remaining work, as it involves several steps that take some time to perform, will be conducted at the Swedish University of Agricultural Sciences during early 2014. The results from the seroprevalence study showed an overall prevalence of 25.1% for goats and 44.2% for sheep. The prevalence has increased compared to an earlier study in the same province in 2010. The precipitation was higher this year than during 2010 which agree with the hypothesis that increased precipitation favour the RVFV spread, as more vectors are hatched. The results from comparable farms showed an increase in seroprevalence for sheep, though not for goats. Older animals showed to have a higher seroprevalence than younger which was expected. The most remarkable finding was the significant differences in prevalence between different farms. Interviews with the animal keepers did not indicate that RVF caused any noticeable health problems in their herds. This study indicates that the virus circulates and causes subclinical infections in sheep and goats in Zambezia. In future research it would be interesting to focus on the big differences between the farms.