title: Spatial analysis and temporal trends of porcine reproductive and respiratory syndrome in Denmark from 2007 to 2010 based on laboratory submission data.
abstract: BACKGROUND
  Porcine reproductive and respiratory syndrome (PRRS) has been a cause for great concern to the Danish pig industry since it was first diagnosed in 1992. The causative agent of PRRS is an RNA virus which is divided into different genotypes. The clinical signs, as well as its morbidity and mortality, is highly variable between herds and regions. Two different genotypes of PRRS virus (PRRSV) are found in Denmark: type 1 and type 2. Approximately 40% of Danish swine herds are seropositive for one or both PRRSV types. The objective of this study was to describe the temporal trend and spatial distribution of PRRSV in Danish swine herds from 2007 to 2010, based on type-specific serological tests from the PRRS surveillance and control program in Denmark using the results stored in the information management system at the National Veterinary Institute, Technical University of Denmark (DTU Vet).
  
  
  RESULTS
  The average monthly seroprevalence of PRRSV type 1 was 9% (minimum of 5%; maximum of 13%) in breeding herds, and 20% (minimum of 14%; maximum of 26%) in production herds; PRRSV type 2 had an average seroprevalence of 3% (minimum of 1%; maximum of 9%) in breeding herds and of 9% (minimum of 5%; maximum of 13%) within production herds. The seroconversion rate followed a similar and consistent pattern, being higher for type 1 than for type 2 for both PRRSV types. Regarding the spatiotemporal results, the relative risk distribution maps changed over time as a consequence of the changes in PRRSV seroprevalence, suggesting a general decline in the extent of areas with higher relative risk for both type 1 and 2. Local spatial analysis results demonstrated the existence of statistically significant clusters in areas where the relative risk was higher for both herds.
  
  
  CONCLUSIONS
  PRRSV type 1 seroprevalence was constantly higher than for PRRSV type 2 in both herd types. Significant spatial clusters were consistently found in Denmark, suggesting that PRRSV is endemic in these areas. Furthermore, relative risk distribution maps revealed different patterns over time as a consequence of the changes in seroprevalence.
authors.affiliation: Section for Epidemiology, National Veterinary Institute, Technical University of Denmark, Bülowsvej 27, 1870, Frederiksberg C, Denmark. aclan@vet.dtu.dk.
authors.forename: Ana Carolina Lopes
authors.initials: AC
authors.lastname: Antunes
authors.affiliation: Section for Epidemiology, National Veterinary Institute, Technical University of Denmark, Bülowsvej 27, 1870, Frederiksberg C, Denmark. tahbh@vet.dtu.dk.
authors.forename: Tariq
authors.initials: T
authors.lastname: Halasa
authors.affiliation: Section for Diagnostic and Scientific Advice, National Veterinary Institute, Technical University of Denmark, Bülowsvej 27, 1870, Frederiksberg C, Denmark. ktla@vet.dtu.dk.
authors.forename: Klara Tølbøl
authors.initials: KT
authors.lastname: Lauritsen
authors.affiliation: Danish Pig Research Centre, SEGES P/S, Vinkelvej 11, 8620, Kjellerup, Denmark. csk@seges.dk.
authors.forename: Charlotte Sonne
authors.initials: CS
authors.lastname: Kristensen
authors.affiliation: Section for Virology, National Veterinary Institute, Technical University of Denmark, Bülowsvej 27, 1870, Frederiksberg C, Denmark. lael@vet.dtu.dk.
authors.forename: Lars Erik
authors.initials: LE
authors.lastname: Larsen
authors.affiliation: Section for Epidemiology, National Veterinary Institute, Technical University of Denmark, Bülowsvej 27, 1870, Frederiksberg C, Denmark. ntoft@vet.dtu.dk.
authors.forename: Nils
authors.initials: N
authors.lastname: Toft
mesh_terms: D000818:Animals; D003718:Denmark / Q000453:epidemiology; D019318:Porcine Reproductive and Respiratory Syndrome / Q000453:epidemiology*; D019316:Porcine respiratory and reproductive syndrome virus / Q000302:isolation & purification*; D016036:Seroepidemiologic Studies; D013552:Swine; D013997:Time Factors