Recommendations for genotyping Trichinella muscle stage larvae

Authors: POZIO, EDOARDO - Istituto Superiore Di Sanita; Zarlenga, Dante

Submitted to: Food and Waterborne Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2019
Publication Date: 3/10/2019
Citation: Pozio, E., Zarlenga, D.S. 2019. Recommendations for genotyping Trichinella muscle stage larvae. Food and Waterborne Parasitology. 15:e00033. https://doi.org/10.1016/j.fawpar.2018.e00033.
DOI: https://doi.org/10.1016/j.fawpar.2018.e00033

Interpretive Summary: Although substantially absent from the domestic food supply, parasites of the genus Trichinella remain an important zoonosis because of the breath of hosts these worms infect, the increase in free range farming, the increasing numbers of feral pigs, and the incidence of infections derived from hunting wild game. As such, there remain endemic areas throughout the world with a high incidence of trichinellosis. Morphology does not provide a means for differentiating parasites of this genus. Because of this and the large number of well recognized species and genotypes within the genus, it has become necessary to pursue simple and effective genetic means to differentiate the species. To this end, a multiplex PCR was developed that accomplishes this goal along with targeting sequencing when more stringent methods are required. The success of this test has prompted the European Union Reference Laboratories to adopt this test as a “best practices” method for differentiating the species. Further, the International Trichinella Reference Center also uses this test for delineating species and genotypes. The International Commission on Trichinellosis has recognized the benefits of this test and opted to develop these instructions and guidelines for unilateral dissemination. This publication is applicable to all who perform studies on Trichinellosis.

Technical Abstract: Being able to identify the species or genotype of Trichinella is of paramount importance not only for epidemiological studies but to better ascertain the source of outbreaks that still occur worldwide. This has become more critical in recent years given the increase in imported meat products and the relationship that wild animals play in the domestic and sylvatic transmission cycles. In contrast to a time when the genus Trichinella was considered monospecific, research in recent years has revealed that the genus consists of 9 species and at least 3 additional genotypes which have yet to be named. Except for a non-encapsulated clade consisting of Trichinella pseudospiralis, Trichinella zimbabwensis, and Trichinella papuae, all members of this genus are morphologically indistinguishable. Thus, identification has been relegated to using PCR and in special cases, DNA sequencing or restriction enzyme digestion. Rather than using a collection of PCR primers specific for each genotype, a single multiplex PCR previously developed for differentiating the major encapsulated and non-encapsulated genotypes has been adopted by the International Commission on Trichinellosis. Since the assay was first developed, other species have been named. Thus, DNA sequencing has been used to validate closely related genotypes. The ICT recommends genotyping be performed as described herein on all outbreaks and whenever Trichinella has been found in consumable foods.