Molecular variation in Trichinella.

The taxonomic status of variants within the genus Trichinella is problematical. Some authors recognise no fewer than four species (Trichinella spiralis, T. pseudospiralis, T. nativa and T. nelsoni), others regard T. nativa and T. nelsoni as strains of T. spiralis (T. spiralis var nativa or sylvatica), while others consider the genus to be monospecific, with a variety of more or less well defined isolates. Much of the current evidence adduced to support these various positions is similar to that used pre-1983. It derives from studies of the incidence of Trichinella infections in wild and in domestic animals, comparisons of infectivity of different isolates in laboratory animals and studies of immunity. However, it has become clear that infectivity and epidemiological studies are unreliable tools for discriminating between isolates of Trichinella and it has been shown that differences in the elicitation of immune responses are as much a function of the host as of the parasite. The introduction of monoclonal antibody technology has, however, permitted the identification of specific antigens in different isolates. The information is as yet scant, and one antigen does not a species make. Isozyme analysis provides some support for separating the various isolates of Trichinella into distinct groups, but cannot of itself shed light on the species problem until certain conditions are met. These conditions are difficult to achieve even in organisms abundantly available and without the baggage of the parasitic habit. Isozyme analysis is probably best used to support the newer studies of genomic DNA. Recent analyses of DNA by restriction endonucleases and dot-blot hybridisation techniques show ample promise of insights into speciation, and a new technique for amplifying the DNA from a single larva by the polymerase chain reaction offers exciting prospects. However, the position yet remains as stated in the first section of this abstract.