General introduction and epidemiology of trichinellosis

All studies on trichinellosis have been based on the assumption that there is only one cosmopolitan agent of human and animal trichinellosis; Trichinella spiralis (Owen, 1835). In the past, swine and only a few synanthropic animals were considered reservoirs, and the presence of the parasite in sylvatic animals was considered rare. Breeding experiments before, and then biochemical approaches (isoenzymes and DNA analysis), showed the presence of a high genetic variability inside this genus, suggesting it be considered as polyspecific. At present, eight gene pools, named from T1 to T8, have been identified in the genus Trichinella. T1 (T. spiralis s str) is the etiological agent for the domestic cycle, with a cosmopolitan distribution related to swine breeding and human habits. However, in some areas this parasite passes from domestic to sylvatic animals and vice versa. Six gene pools are the agents for the sylvatic cycle at different latitudes, mainly in carnivores. T2 (T. nativa) is present in terrestrial mammals and seldom in sea mammals of arctic and subarctic regions. T3, T5, and T8 are present mainly in Canidae (T3), Ursidae (T5), Hyaenidae and Felidae (T8) of temperate-subtropical areas of Palearctic, Nearctic and South African regions, respectively. T6 is present in carnivores in the subarctic-temperate area of the Nearctic region; and T7 (T. nelsoni) in Hyaenidae and Felidae of Equatorial Africa. Only T4 (T. pseudospiralis) can infect both mammals and birds, and it shows a cosmopolitan distribution. Probably trichinellosis is present world-wide, but unknown in those areas where it has not been sought.