Two genotypes were recognised (type 1 or European, and type 2 or North-American). Type 1 is the predominant genotype in Europe while type 2 is the most prevalent in America and Asia.
Nowadays, they are designated as two different virus species: PRRSV1 and PRRSV2. Within PRRSV1, at least 4 different subtypes have been reported; subtype I is predominant in Western Europe whereas subtypes II, III and IV have been isolated only in countries eastwards of Poland until now. Regarding PRRSV2, two clades have been described.