Trichinella spp.
(worldwide distribution maps)

Trichinella spiralis (T-1) (green) is the most common member of the genus. The world distribution as depicted is almost certainly an under-representation. The isolate has a low tolerance to freezing, but has a high reproductive potential in swine, laboratory rats, and laboratory mice. It is the primary cause of domestic animal trichinosis although it also occurs in sylvatic hosts.	Trichinella nativa (T-2) (yellow) is a Holarctic species with a very high resistance to freezing. It is common in carnivores and has a low infectivity for swine and rats. Trichinella nelsoni (T-7) (red) is found in subsaharan Africa. It has no tolerance to freezing, a relatively high tolerance to heat, primarily infects Hyaenidae and Felidae, and has a low infectivity for swine and rats. Trichinella murrelli (T-5) (green) is found in North America. Its range probably extends down into Mexico. It has a low tolerance to freezing, primarily infects carnivores, and has a very low reproduction in swine and rats.
A Trichinella isolate, termed T-6 (red), is similar to T. nativa. It, too, has a relatively high tolerance to freezing and primarily infects carnivores. It is also capable of interbreeding with T. nativa. Nonetheless, several molecular differences exist between the two. Trichinella britovi (T-3) (green) occurs in Eurasia and has been introduced into Africa. It is common in sylvatic carnivores, and occasionally infects domestic animals. It has a low infectivity for rats, moderate infectivity for swine, and a moderately good tolerance to freezing. Isolates capable of interbreeding with T. britovi include T-9 (purple) in Japan and T-8 (yellow) from carnivores in Southern Africa. Some molecular differences exist between these two genotypes and T. britovi. T-9 from Japan is actually more similar to T. murrelli than to T. britovi.	Three non-encapsulating Trichinella species exist. Trichinella pseudospiralis (T-4) (red dots) infects over a dozen species of mammals, as well as raptors, some passeriform birds, and chickens. It has moderate infectivity for swine, rats, and mice. Several genetically distinct populations are known to occur. Trichinella papuae (T-10) (yellow) was originally isolated from a wild pig and has larvae somewhat larger than T. pseudospiralis. Though capable of infecting laboratory mice, it is unable to infect chickens but can infect some reptiles. Trichinella zimbabwensis (green) is the third known non-encapsulated species. It known to naturally infect reptiles in Africa, but experimentally it can also infect some mammals.