The genus Trichinella has genetically distinguished but taxonomically still undetermined genotypes other than usual species
The biggest morphological classification is based on the presence/absence of collagen capsule surrounding the pathogen in cysts in infected muscles
※Manson's Tropical Infectious Diseases 24th ed. (published in 2023) describes that T. spiralis has several subspecies but according to NCBI Taxonomy Browser and the following articles subspecies written in Manson's are classified as species.
Pozio, E., Rosa, G. la, Murrell, K. D., & Lichtenfels, J. R. (1992). Taxonomic Revision of the Genus Trichinella. The Journal of Parasitology, 78(4), 654. https://doi.org/10.2307/3283540
Zarlenga, D., Thompson, P., & Pozio, E. (2020). Trichinella species and genotypes. Research in Veterinary Science, 133, 289–296. https://doi.org/10.1016/j.rvsc.2020.08.012
Encapsulated
Non-encapsulated
Infect only mammals
Infect birds and mammals
Trichinella spiralis
Trichinella nativa
Trichinella nelsoni
Trichinella britovi
Trichinella murrelli
Trichinella patagoniensis
Trichinella genotype T6
Trichinella genotype T8
Trichinella genotype T9
Trichinella pseudospiralis
Trichinella papuae
Trichinella zimbabwensis
Epidemiology
Since Trichinella infections often cause asymptomatic or mild disease and no serological tests with high performance is available, true epidemiology of human trichinellosis is thought still underestimated.
Trichinellosis distributes worldwide from arctic region through the tropics.
Human trichinellosis in developed countries has been dramatically decreased due to improvement of farming and slaughtering of domestic pigs and shrinkage of backyard pig farming in private facilities.
Yayeh, M., Yadesa, G., Erara, M., Fantahun, S., Gebru, A., & Birhan, M. (2020). Epidemiology, diagnosis and public health importance of Trichinellosis. Journal of World’s Poultry Research, 10(3), 131–139. https://doi.org/10.36380/scil.2020.ojafr18
Life cycle and Transmission
Life cycle is maintained amongst host mammals and birds.
Pigs and rats (domestic cycle) or wild bores, wild bears, polar bears, rats and birds (sylvatic cycle).
Transmission to human occurs by ingestion of raw or undercooked meat including pigs, wild bores, horse, dog, bear, polar bear, badger and soft-shelled turtle (スッポン).
Rostami, A., Gamble, H. R., Dupouy-Camet, J., Khazan, H., & Bruschi, F. (2017). Meat sources of infection for outbreaks of human trichinellosis. Food Microbiology, 64, 65–71. https://doi.org/10.1016/j.fm.2016.12.012
The world-first report of trichinellosis originated from soft-shelled turtle was published in Japan in 2009 (but only in Japanese and neglected from English literature).
