title: Serosurveillance of Schmallenberg virus in Switzerland using bulk tank milk samples.
abstract: Infections with Schmallenberg virus (SBV), a novel Orthobunyavirus transmitted by biting midges, can cause abortions and malformations of newborns and severe symptoms in adults of domestic and wild ruminants. Understanding the temporal and spatial distribution of the virus in a certain territory is important for the control and prevention of the disease. In this study, seroprevalence of antibodies against SBV and the spatial spread of the virus was investigated in Swiss dairy cattle applying a milk serology technique on bulk milk samples. The seroprevalence in cattle herds was significantly higher in December 2012 (99.5%) compared to July 2012 (19.7%). This high between-herd seroprevalence in cattle herds was observed shortly after the first detection of viral infections. Milk samples originating from farms with seropositive animals taken in December 2012 (n=209; mean 160%) revealed significantly higher S/P% ratios than samples collected in July 2012 (n=48; mean 103.6%). This finding suggests a high within-herd seroprevalence in infected herds which makes testing of bulk tank milk samples for the identification farms with past exposures to SBV a sensitive method. It suggests also that within-herd transmission followed by seroconversion still occurred between July and December. In July 2012, positive bulk tank milk samples were mainly restricted to the western part of Switzerland whereas in December 2012, all samples except one were positive. A spatial analysis revealed a separation of regions with and without positive farms in July 2012 and no spatial clustering within the regions with positive farms. In contrast to the spatial dispersion of bluetongue virus, a virus that is also transmitted by Culicoides midges, in 2008 in Switzerland, the spread of SBV occurred from the western to the eastern part of the country. The dispersed incursion of SBV took place in the western part of Switzerland and the virus spread rapidly to the remaining territory. This spatial pattern is consistent with the hypothesis that transmission by Culicoides midges was the main way of spreading.
authors.affiliation: Federal Food Safety and Veterinary Office FSVO, Schwarzenburgstrasse 155, CH-3003 Bern, Switzerland.
authors.forename: Sandra
authors.initials: S
authors.lastname: Balmer
authors.affiliation: Institute of Virology and Immunology IVI, Sensemattstr. 293, CH-3147 Mittelhäusern, Switzerland.
authors.forename: Andrea
authors.initials: A
authors.lastname: Vögtlin
authors.affiliation: Institute of Virology and Immunology IVI, Sensemattstr. 293, CH-3147 Mittelhäusern, Switzerland.
authors.forename: Barbara
authors.initials: B
authors.lastname: Thür
authors.affiliation: Federal Food Safety and Veterinary Office FSVO, Schwarzenburgstrasse 155, CH-3003 Bern, Switzerland.
authors.forename: Martina
authors.initials: M
authors.lastname: Büchi
authors.affiliation: Suisselab AG Zollikofen, Schützenstrasse 10, CH-3052 Zollikofen, Switzerland.
authors.forename: Carlos
authors.initials: C
authors.lastname: Abril
authors.affiliation: Suisselab AG Zollikofen, Schützenstrasse 10, CH-3052 Zollikofen, Switzerland.
authors.forename: Matthias
authors.initials: M
authors.lastname: Houmard
authors.affiliation: Federal Food Safety and Veterinary Office FSVO, Schwarzenburgstrasse 155, CH-3003 Bern, Switzerland.
authors.forename: Jürg
authors.initials: J
authors.lastname: Danuser
authors.affiliation: Federal Food Safety and Veterinary Office FSVO, Schwarzenburgstrasse 155, CH-3003 Bern, Switzerland. Electronic address: heinzpeter.schwermer@blv.admin.ch.
authors.forename: Heinzpeter
authors.initials: H
authors.lastname: Schwermer
mesh_terms: D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D002044:Bunyaviridae Infections / Q000097:blood / Q000453:epidemiology / Q000662:veterinary*; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology* / Q000821:virology*; D002519:Ceratopogonidae / Q000821:virology; D016000:Cluster Analysis; D003612:Dairying; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D007303:Insect Vectors / Q000821:virology; D008892:Milk / Q000821:virology*; D016851:Orthobunyavirus / Q000276:immunology* / Q000472:pathogenicity; D016036:Seroepidemiologic Studies; D062211:Spatio-Temporal Analysis; D013557:Switzerland / Q000453:epidemiology
chemical_list: D000914:Antibodies, Viral
keywords: Cluster analysis; Culicoides; Disease incursion; ELISA; Orthobunyavirus; Ruminants; Semivariogram; Seroconversion; Seroprevalence; Spatial spread