The analysis of genetic, biochemical, and biological data on about 300 Trichinella isolates, reported in the literature, allows a taxonomic revision of this genus. We propose the recognition of 5 sibling species, Trichinella spiralis (Owen, 1835) sensu stricto; Trichinella nativa Britov and Boev, 1972; Trichinella pseudospiralis Garkavi, 1972; Trichinella nelsoni Britov and Boev. 1972 sensu stricto: and Trichinella britovi n. sp., on the basis of biochemical and biological characteristics. Trichinella britovi n. sp. is characterized by distribution in the Palaearctic Region; newborn larvae (NBL) production in vitro of 35-55 NBL/72 hr; nurse cell development time (NC d.t.) between 24 and 42 days postinfection (d.p.i.); low reproductive capacity index (RCI) in mice, rats. and pigs; low resistance to freezing; 1 unique marker allozyme; and moderate pathogenicity for humans. The new species is most similar to Trichinella nativa but differs from it in 4 allozymes, in having less resistance to freezing, in having a different pattern of major ribosomal DNA fragments after endonuclease digestion, and in distribution area. Trichinella nativa is characterized by a holarctic distribution; hosts that are sylvatic mammals; NBL production in vitro 28-54/72 hr; NC d.t. between 20 and 30 d.p.i.; low RCI in mice, rats, and pigs; high resistance to freezing; 2 unique marker allozymes; and moderate to severe pathogenicity for humans. Trichinella spiralis sensu stricto is characterized by a cosmopolitan distribution in domestic pigs, associated wildlife, and humans; high NBL production in vitro (> 90 NBL/72 hr); NC d.t. between 16 and 37 d.p.i.; high RCI in mice, rats, and pigs; no resistance to freezing; 6 unique marker allozymes; and high pathogenicity for humans. Trichinella pseudospiralis is characterized by a cosmopolitan distribution in wild birds and mammals; NBL production in vitro of 35-60 NBL/72 hr; absence of NC; RCI in mice and rats higher than in other sylvatic species; low RCI in pigs; no resistance to freezing; and 12 unique marker allozymes. Pathogenicity in humans is unknown. Trichinella nelsoni sensu stricto is distributed only in equatorial Africa in wild mammals, and it has NBL production in vitro of 49-60 NBL/72 hr; NC d.t. between 34 and 60 d.p.i.; low RCI in mice, rats, and pigs; no resistance to freezing; 4 unique marker allozymes; and moderate pathogenicity for humans. Three additional phenotypes, named T5, T6, and T8, have been recognized in this genus, but at present their taxonomic level is uncertain.
