Scientific achievements of the last 60 years: From a single to a multispecies concept of the genus Trichinella.

The scientific basis that led to the development of a multispecies concept within the Trichinella genus originated in the 1950s, when scientists began reporting an increasing number of host-specific peculiarities among different geographic isolates. This led to speculation that important geographic variability existed within Trichinella spiralis, the only species in the genus at that time. Comparative infection results sparked great interest among investigators and led to similar studies using various geographic isolates of the parasite. In 1972, the Russian scientists V.A. Britov, S.N. Boev and B.L. Garkavi, described three new species: Trichinella nativa, Trichinella nelsoni and Trichinella pseudospiralis. This shattered the concept that the genus Trichinella was monospecific and widened the host range to include birds. The description of these new species generated an intense debate over their taxonomic validity because there were no clear morphological differences among them and because the concept of sibling species had not yet been accepted by parasitologists. The resolution of the taxonomic issues was facilitated by the adoption of new biochemical and molecular techniques for systematics research. In 1992, the first study comparing 152 isolates from various host species and geographical regions identified eight distinct taxa, coded T1 through T8; four of these represented the previously proposed species and included one new species, Trichinella britovi (T3). During the past 27 years, an increasing number of investigations in different geographical regions and hosts coupled with the availability of new and highly sensitive molecular techniques have allowed the description of four new species; Trichinella murrelli (T5), Trichinella papuae (T10), Trichinella zimbabwensis (T11) and Trichinella patagoniensis (T12), and two new genotypes Trichinella T9 and T13. Thus, the taxonomic status of Trichinella T6, T8, T9 and T13 remain unresolved. These new technologies have also advanced a more complete phylogenetic, zoogeographical and epidemiological knowledge base for future work.