Emergence and Consequences of Schmallenberg Virus Infection in Ruminants in North Rhine-Westphalia
Weigelin, Barbara Edda
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The Schmallenberg virus, firstly detected in 2011 in a cattle herd close to Schmallenberg (North-Rhine-Westphalia, Germany), is a newly emerged Orthobunya virus (family Bunyaviridae) that is transmitted by blood-sucking insects and causes mild clinical symptoms in adult cows. Affected ruminants abort fetuses with serious congenital malformations such as athrogryphosis, brachygnathia inferior, torticollis, kyphosis, lordosis, scoliosis, muscle hypoplasia, cerebellar and cerebral hypoplasia, hydrancephaly, porencephaly, hydrocephalus, and micromyelia. The first vaccines have been developed but are still in the testing period. Based on epidemiological data from the European Food Safety Authority (EFSA), SBV infections between August 1, 2011 and April 30, 2013 were analysed. Three ranking models (geographical, seasonal and projection model) were used to grade SBV infections regarding to animal welfare and production, such as service, milk yield and dystocia. The diagnosis of SBV infection lays on exclusion of other viruses causing similar diseases, recognition of clinical signs and the use of a commercial ELISA kits for the detection of anti-Schmallenberg virus antibodies in serum and plasma as well as on direct virus determination from aborted fetuses, newborns and placenta by RT- PCR. Histology showed astrogilosis and microgliosis in the central nervous system of infected bovine and ovine newborns. In some cases myofibrillar hypoplasia in the skeletal muscle was found. In sheep, lymphohistological inflammation in the central nervous system and glial nodules in the hippocampus and mesencephalon were shown. Fetal malformations during gestation caused severe consequences on the reproductive performance in infected herds. A transplancental infection in the tetragonic determination phase causes embryonal/fetal malformation between 28 and 36 days in sheep, between 30 and 50 days in goats, and between 75 and 110 days in cattle. In case of dead bovine fetuses fetotomy must be considered. It could be proved that infections of the dam at an early stage of gestation leads to damages of the central nervous system of the embryo/fetus while later the damage of the skeletal and muscular system develops. Due to the appearance of this new virus, further studies are needed to determine the risk of transmission of SBV and the impact of the virus on fertility in ruminants.