Abstract:
Background: Orthobunyaviruses belonging to the Simbu sero-group occur worldwide, including the newly
recognized Schmallenberg virus (SBV) in Europe. These viruses cause congenital malformations and reproductive losses
in ruminants. Information on the presence of these viruses in Africa is scarce and the origin of SBV is unknown. The aim
of this study was to investigate the presence of antibodies against SBV and closely related viruses in cattle in Tanzania,
and their possible association with reproductive disorders.
Results: In a cross-sectional study, serum from 659 cattle from 202 herds collected in 2012/2013 were analyzed using a
commercial kit for SBV ELISA, and 61 % were positive. Univariable logistic regression revealed significant association
between ELISA seropositivity and reproductive disorders (OR = 1.9). Sera from the same area collected in 2008/2009,
before the SBV epidemic in Europe, were also tested and 71 (54.6 %) of 130 were positive. To interpret the ELISA
results, SBV virus neutralization test (VNT) was performed on 110 sera collected in 2012/2013, of which 51 % were
positive. Of 71 sera from 2008/2009, 21 % were positive. To investigate potential cross reactivity with related viruses, 45
sera from 2012/2013 that were positive in SBV ELISA were analyzed in VNTs for Aino, Akabane, Douglas, Peaton, Sabo,
SBV, Sathuperi, Shamonda, Simbu and Tinaroo viruses. All 45 sera were positive for one or more of these viruses.
Twenty-nine sera (64.4 %) were positive for SBV, and one had the highest titer for this virus.
Conclusions: This is the first indication that Aino, Akabane, Douglas, Peaton, Sabo, SBV, Sathuperi, Shamonda and
Tinaroo viruses circulate and cause negative effect on reproductive performance in cattle in Tanzania. SBV or a closely
related virus was present before the European epidemic. However, potential cross reactivity complicates the
interpretation of serological studies in areas where several related viruses may circulate. Virus isolation and molecular
characterization in cattle and/or vectors is recommended to further identify the viruses circulating in this region.
However, isolation in cattle is difficult due to short viremic period of 2 to 6 days, and isolation in vectors does not
necessarily reflect the situation in cattle.
