Seroprevalence of Schmallenberg Virus Antibodies among Dairy Cattle, the Netherlands, Winter 2011–2012

Infections with Schmallenberg virus (SBV) are associated with congenital malformations in ruminants.Because reporting of suspected cases only could underestimate the true rate of infection, we conducted a seroprevalence study in the Netherlands to detect past exposure to SBV among dairy cattle.A total of 1,123 serum samples collected from cattle during November 2011-January 2012 were tested for antibodies against SBV by using a virus neutralization test; seroprevalence was 72.5%.Seroprevalence was signifi cantly higher in the central-eastern part of the Netherlands than in the northern and southern regions (p<0.001).In addition, high (70%-100%) within-herd seroprevalence was observed in 2 SBV-infected dairy herds and 2 SBV-infected sheep herds.No signifi cant differences were found in age-specifi c prevalence of antibodies against SBV, which is an indication that SBV is newly arrived in the country.D uring the last 2 weeks of August and the fi rst 2 weeks of September 2011, dozens of veterinary practitioners in the Netherlands reported to a monitoring help desk (GD Veekijker) that several dairy herds with cows showed a sudden decrease in milk production, watery diarrhea, and occasional fever (1).The affected animals recovered, and extensive bacteriologic, virologic, and parasitologic testing of feces and blood samples of sick cows did not reveal an infectious cause for the clinical signs.Similar problems were reported at about the same time in Germany, and on November 18, 2011, the Friedrich Loeffl er Institute (Greifswald, Germany) reported the detection of a novel orthobunyavirus that could be the cause of the clinical problems (2).Real-time reverse transcription PCR (RT-PCR), made available by the Friedrich Loeffl er Institute, was used to test stored blood samples (N = 50) from the clinically diseased cattle in the Netherlands; 36% had positive test results.Since then, the virus has also been associated with congenital malformations in young animals (lambs, goat kids, and calves) (3).The new virus is provisionally called Schmallenberg virus (SBV), or Shamonda-like virus.It is a RNA virus and shows 97% identity with Shamonda virus (SHAV) (small gene segment), 71% identity with Aino virus (medium gene segment), and 69% identity with Akabane virus (AKAV) (large gene segment) (4).All these viruses are part of the Simbu serogroup of the family Bunyaviridae, genus Orthobunyavirus.The Simbu serogroup is composed of several arthropod-borne viruses (arboviruses, including SHAV, AKAV, and Aino virus) transmitted by Culicoides spp.biting midges and mosquitos.SHAV was initially isolated from cattle and Culicoides spp.biting midges in Nigeria in the 1960s (5,6).In 2002, SHAV emerged in Japan and was isolated from Culicoides spp.biting midges Seroprevalence of Schmallenberg Virus Antibodies among Dairy Cattle, the Netherlands, Winter