Distribution of genotypes of porcine reproductive and respiratory syndrome virus in Ontario during 2004-2007 and the association between genotype and clinical signs of disease.

Restriction fragment length polymorphism (RFLP) was first proposed to classify porcine reproductive and respiratory syndrome virus (PRRSV) in 1998. The primary objective of this study was to identify associations between different PRRSV RFLP types in swine herds in southern Ontario and clinical signs of disease in those herds. Herds included in the study submitted samples to the Animal Health Laboratory at the University of Guelph between September 2004 and August 2007. Each farm owner was surveyed to describe the clinical disease in the herd and the RFLP pattern of an isolate of PRRSV was obtained from a diagnostic sample. The most frequent isolates were RFLP types 1_4 (25.1%), 252 (14.7%), 134 (12%), and 1_2 (7.7%). The distribution of RFLP types in this study was found to be different from a previous investigation in Ontario. Those RFLP types most associated with clinical disease in the farrowing phase of production were 1_4, 1_2, and 134. The only virus type to be significantly associated with disease in the finisher phase was RFLP type 262. During the study period RFLP type 184 emerged in the population in November 2005.