Schmallenberg virus among ruminants in the Gaza province, Mozambique

Sammanfattning: Schmallenberg virus was discovered in North Rhine-Westphalia in Germany in 2011. The virus spread over most of Europe during the following years, including United Kingdom and the Nordic countries. Its origins are yet to be discovered. Schmallenberg virus belongs to the Simbu serogroup of the Bunyaviridae family, genus Orthobunyavirus. Where, exactly, on the phylogenetic tree of Simbu serogroup viruses it should be placed is not concluded, but its closest relatives seem to be Shamonda virus, Aino virus, Akabane virus and Sathuperi virus. The susceptible species are primarily ruminants, but Schmallenberg virus and its antibodies have occasionally been found in dogs. No evidence of zoonotic potential has been found. The virus is mainly transmitted by different species of biting midges of the genus Culicoides. Transplacental transmission can occur during the early part of pregnancy in ruminants, after placentomes have been formed. Infectious Schmallenberg virus has also been found to be shed in semen of cattle and sheep, thus horizontal transmission is possible in theory but has not yet been proven experimentally. Clinical symptoms in adult cattle, sheep and goats are usually mild or absent, lasts only a few days and includes fever, reduced milk yield and diarrhoea. Transplacental transmission can, but does not always, lead to congenital Schmallenberg. If it does, the most common symptoms are malformations such as arthrogryposis (joint deformity/contracture) and different malformations of the vertebral column and brain. Reduced body weight in affected calves at birth seems to be correlated to the severity of the malformations. Infected foetuses are sometimes aborted or stillborn. Schmallenberg virus antibodies are detectable by indirect methods such as ELISA and virus neutralization test. Cross reactions with antibodies directed against other viruses of the Simbu serogroup are known to occur. In the present study, seroprevalence for Schmallenberg virus in the Gaza province in southern Mozambique was investigated in cattle, sheep and goats, using competitive Schmallenberg ELISA. The overall seroprevalence in cattle was approximately 90 %, in sheep close to 60 % and almost 75 % in goats. All investigated herds and flocks had seropositive animals. Detection of Schmallenberg viral RNA is possible by real-time RT-PCR, either specific for just Schmallenberg virus, or a general pan-Simbu real-time RT-PCR. Some samples in the present study that were positive in competitive ELISA were analysed using pan-Simbu real-time RT-qPCR. None of the included samples gave a positive result in the PCR. The findings in this study show that antibodies able to produce a positive result in Schmallenberg virus ELISA circulates the Gaza province in Mozambique. The virus responsible for the positive results might be Schmallenberg virus, but it can as well be one or many other Simbu serogroup viruses. Cross reactivity cannot be ruled out, but is on the contrary quite possible, since other members of the Simbu serogroup are known to circulate in Africa. Further studies in Mozambique, or other parts of southern Africa, would be of interest to determine which virus or viruses that are causing the positive ELISA results. Virus neutralization tests can be used to investigate which Simbu serogroup virus or viruses that are circulating the area. Schmallenberg virus and Simbu serogroup virus detection is of even greater interest, but this might prove difficult due to the short viremic period of Schmallenberg virus and other Simbu serogroup viruses. Since Schmallenberg virus shedding in semen can continue for more than two months in some individuals, virus detection in semen might be a viable way. Virus detection in the vector can also be possible to achieve, especially if very many biting midges are included.