Porcine reproductive and respiratory syndrome (PRRS) is considered to be one of the economically most important swine disease. The etiological agent, PRRS virus, has an extreme genetic variability, that seriously affects diagnostics and control of this disease. Two genotypes of PRRSV were distinguished, namely Type 1, dominating in Europe and Type 2, dominating in North America but also identified in Asia. Type 1 has been further divided into subtype 1, common in Central and Western Europe, and relatively recently described subtypes 2-4, present in Eastern European countries. New data have clearly shown that PRRSV strains of subtypes 2 and 3, that are circulating in countries bordering with Poland, have much higher pathogenicity when compared to classical PRRSV strains present in most European countries. This paper summarizes results of experimental studies focusing on the characteristics of the new, more pathogenic PRRSV subtypes, and presents data on their detection and control.