A screening for Schmallenberg Virus among sheep and goats in Tanzania
Schmallenberg virus (SBV) is a novel arthropod-borne orthobunyavirus emerging in Europe in 2011 to 2012. Acute SBV infection causes diarrhoea, fever and reduced milk production in dairy cattle, but it is mainly the reproductive disorders (abortions, malformed foetuses and stillborn animals) in ruminants that have caused substantial economical losses. The prevalence of the virus outside of Europe is poorly investigated. SBV or SBV-like antibodies were detected in Mozambique in 2013, which raised interest for a similar study in Tanzania.
In this study in Tanzania, blood samples were collected from 478 sheep and goats from 39 herds in 15 different villages in three districts, covering areas in the north, south and east of Tanzania. The epidemiology of the virus was investigated by tracing antibodies by ELISA and mapping of the virus by PCR was started. In total 309 serum samples were analysed by a competitive ELISA. The overall seroprevalence was 43% by this test. Seropositive herds were found in all areas. In Mikumi in the east, all herds were positive for SBV antibodies, in Ngorongoro in the north, 64% were positive and in Mahenge in the south were 85% positive. In total 127 of the tested samples were additionally analysed by an indirect ELISA. The results between the two ELISAs differed more than expected. The overall seroprevalence was 21% by the indirect ELISA. This divergent result is not supported by other studies comparing different SBV ELISAs, and the fact that the sensitivity and specificity are similar for both tests contradicts the result. In total 68 buffy coats from herds seropositive by both ELISAs were analysed by PCR. All analysed samples were negative in the Pan-Simbu RT-PCR.
The findings in this study indicate that SBV is endemic in Tanzania. However cross-reactivity with viruses related to SBV cannot be ruled out as cause of the positive ELISA results.