Seven species belonging to the Trichinella genus (five with encapsulated larvae and two with non-encapsulated larvae in host muscles) and three additional genotypes have been described to date: T. spiralis (genotype T1), a cosmopolitan species with a high infectivity to swine and rats; T. nativa (T2), etiological agent of sylvatic trichinellosis in arctic and subarctic areas of the Holarctic region, and its related genotype (Trichinella T6), detected in Alaska, Idaho, Montana, Pennsylvania, Wyoming, and Ontario; T. britovi (T3), etiological agent of sylvatic trichinellosis in temperate areas of Europe and Asia, and its related genotypes Trichinella T9 in Japan and Trichinella T8 in South Africa and Namibia; T. murrelli (T5), etiological agent of sylvatic trichinellosis in temperate areas of the USA; T. nelsoni (T7), etiological agent of sylvatic trichinellosis in Africa south of the Sahara; T. pseudospiralis (T4), a non-encapsulated cosmopolitan species infecting both mammals and birds; and T. papuae (T10), a recently discovered non-encapsulated species in sylvatic swine of Papua New Guinea. In the Southeast Asia and Australian regions, T. spiralis, T. pseudospiralis and T. papuae have been detected in sylvatic and domestic animals and in humans. A focus of human trichinellosis due to T. papuae was recently discovered in Papua New Guinea, with a prevalence of 28.9%. Trichinellosis has also been documented in domestic animals and/or humans in Cambodia, Indonesia (Bali and Sumatra), Lao PDR, Malaysia, Myanmar, Thailand, and New Zealand, and in wildlife of Tasmania.
There are few small animals models for filariasis, even more so for onchocerciasis. Therefore it is difficult to test under drug screening conditions large numbers of potentially macrofilaricidal compounds. One way around this difficulty is to use mice infected with Trichinella spiralis which by reason of anatomical location in the host would show some correlation in antinematode activity between the test and target organisms. This study investigated the activity of 16 compounds against the immature larval stage of T. spiralis. All the nine benzimidazole compounds (albendazole, flubendazole, mebendazole, oxfendazole, oxibendazole 780118, 780120, 790163, and 790392) were active, the most potent being oxfendazole. The benzothiazoles (CGP21306, CGP20376, CGP21833 and CGP24588A) also indicated some anti-nematode activity together with 35vr, an imidazopyridine, but not as marked as the benzimidazole group. However, the organic arsenical compounds (Mel Ga and Mel Ni) showed little activity and this was at a rather highly toxic level. The prospects of using the Trichinella-mouse model as a primary screen to test for potential macrofilaricides are discussed.
Previously, we reported the presence of imported trichinellosis in a Thai worker returning from Malaysia, who presented with progressive generalized muscle hypertrophy and weakness after eating wild boar meat. This work analyzed a partial small subunit of a mitochondrial ribosomal RNA gene of Trichinella larvae isolated from the patient. The results showed complete identity with a mitochondrial RNA gene of Trichinella papuae (GenBank accession no. EF517130). This is the first report of imported trichinellosis in Thailand caused by T. papuae. It is possible that T. papuae is widely distributed in the wildlife of Southeast Asia.