The aim of the surveillance and control programme for SBV in 2018 is to document if SBV has circulated or re-emerged in Norway, and to estimate the proportion of seropositive dairy herds, after the epidemic in 2012.
Schmallenberg virus (SBV) is an arthropod born virus in the genus
Orthobunyavirus and is a member of Simbu serogroup viruses. Midges ( Cullicoides spp.) act as vectors. Vertical transmission occurs through placenta. The virus causes subclinical infection or mild non-specific clinical signs in cattle and sheep during the vector season. In pregnant cattle, sheep, goats and bison, SBV causes stillbirth and congenital malformations. Disease caused by Schmallenberg virus is not notifiable in Norway.
Orthobunyavirus of the Simbu serogroup was not detected in Europe before 2011. Schmallenberg virus was first identified in Germany and the Netherlands from dairy cattle diseased in summer and autumn of 2011. Soon after, presence of SBV was confirmed in new-born lambs with congenital malformations. From Germany and the Netherlands SBV rapidly spread to many European countries.
In Norway, Schmallenberg virus was detected in midges in September 2012. Two months later, a high proportion (17.3%) of dairy herds in the southern part of the country were seropositive for SBV. Retrospective analysis of some of these herds showed that they had seroconverted in the previous summer months. In the following winter, a calf was born with malformations due to Schmallenberg virus infection.
After the SBV epidemic in 2012, bulk milk analyses revealed no infected dairy farm further north along the west coast of Norway. A total of 60 samples of midges collected at five locations in southern Norway in 2013 were negative for SBV. No clinical case of Schmallenberg disease, or deformations in newborn ruminants due to SBV, was recorded. Surveillance in 2016 showed that the prevalence of bulk milk positive herds had declined. However, abortions in seropositive cows, and positive bulk milk samples from previously negative farms, indicated that the virus could have circulated in Norway after the epidemic in 2012.
The Norwegian Food Safety Authority is responsible for carrying out the surveillance programme for SBV. The Norwegian Veterinary Institute is in charge of designing the programme, collecting the bulk milk samples from the dairies and performing the tests. Blood samples from cattle herds were collected by inspectors from the Norwegian Food Safety Authority.