Genetic evidence of interspecies introgression of mitochondrial genomes between Trichinella spiralis and Trichinella britovi under natural conditions

Trichinellosis is a zoonotic disease caused by Trichinella muscle larvae (ML) through ingestion of raw or undercooked meat. To date, 12 taxa are recognized in this genus, of which four are circulating in Europe (Trichinella spiralis, Trichinella nativa, Trichinella britovi and Trichinella pseudospiralis). T. spiralis and T. britovi circulate in European wildlife and occur simultaneously in the same host species. The possibility of hybrid formation between T. britovi and T. spiralis has hardly been addressed and so far, results of experimental hybridisation attempts between T. britovi and T. spiralis are inconclusive. The aim of the present study was to analyse molecular polymorphisms of single T. spiralis and T. britovi ML from natural infections based on nuclear 5S rDNA intergenic spacer region (5S rDNA-ISR) and mitochondrial cytochrome c oxidase 1 (CO1) gene sequences. Six haplotypes of the 5S rDNA intergenic spacer region (5S rDNA-ISR) and 14 of the cytochrome c oxidase 1 (CO1) gene were demonstrated in 89 individual T. britovi ML from Latvia and Poland. In contrast, only two haplotypes were observed at both 5S rDNA-ISR and CO1 of 57 individual T. spiralis ML from Polish wild boar and red foxes. Moreover, this study demonstrates hybridisation in eight individual ML between T. britovi and T. spiralis under natural conditions in four Polish wild boar and two red foxes, revealed by combining 5S rDNA-ISR and CO1 sequence information of individual Trichinella ML. To our knowledge, this is the first report of interspecies hybridisation between T. spiralis and T. britovi under field conditions.