Intraspecific genetic variation in Trichinella spiralis and Trichinella britovi populations circulating in different geographical regions of Poland

Trichinella spiralis and Trichinella britovi are species of nematodes which are responsible for the majority of Trichinella infections in the world and the most prevalent in Poland. The most abundant species – T. spiralis, is considered to be more genetically homogeneous in Europe than T. britovi. The aim of the present study was to determine the genetic variability in T. spiralis and T. britovi populations based on nuclear 5S rDNA intergenic spacer region (5S rDNA) and cytochrome c oxidase 1 (COX1) gene sequences. For the study, 55 isolates of T. spiralis and 50 isolates of T. britovi isolated from wild boars, pigs, brown rat and a red fox were analyzed. Based on the analysis of both genes, the genetic variability within populations of T. spiralis and T. britovi differed. In T. spiralis, two single nucleotide polymorphisms (SNPs) were observed in the 612 bp 5S rDNA gene fragment, and one SNP was detected in the 700 bp COX1 gene fragment. In T. britovi, 17 single nucleotide variations (SNVs) were detected in the 5S rDNA gene fragment (among them 16 SNPs), while COX1 sequence analysis revealed the occurrence of 20 SNVs between the sequences tested (among them 19 SNPs). For the majority of T. spiralis isolates the investigated larvae presented uniform haplotypes. In contrast, most of the isolates of T. britovi consisted of larvae of different haplotypes. Geographical analysis showed that each region exhibited different haplotype composition and richness. Warmińsko-Mazurskie and Zachodniopomorskie regions were the richest in haplotypes (15 and 16 haplotypes, respectively). We used heatmaps showing a characteristic pattern for each region graphically. This may allow to differentiate regions based on the occurrence of particular haplotypes. Furthermore, a PCA analysis on the SNP level yielded biplots that show that certain haplotypes/genotypes are associated with (clusters of) regions.