EN
The definition of the porcine respiratory disease complex (PRDC) is presented and compared with diseases caused by a single etiological viral or bacterial agent. The classification of viruses or bacteria participating in the multifactorial etiology of disease complexes, among them PRDC, include microorganisms initiating the pathological process, as well as a second group of microorganisms, following after the primary destruction of the resistance to infection, that joins in the pathogenesis of the pathological complex. Another grouping takes into account the higher and lower importance of the etiological agents in causing disease and losses in animal production. The role of the following microorganisms participating in the etiology of PRDC is defined as follows: Porcine reproductive and respiratory syndrome virus, Swine influenza virus, Aujeszky disease virus, Porcine circovirus type 2, Porcine respiratory corona virus, Porcine cytomegalovirus, Mycoplasma hyopneumoniae, Bordetella bronchiseptica, Pasteurella multocida, Haemophilus parasuis, Streptococcus suis, Actinobacillus suis, Arcanobacterium pyogenes and Salmonella spp. Data on simultaneous bacterial-bacterial interactions, viral-viral interactions, and bacterialviral interactions are discussed.