Preliminary Analysis of the Molecular Phylogenetics of Toxocara canis (Nematoda: Ascaridoidea) Using Nuclear Ribosomal Second Internal Transcribed Spacer Sequences

Abstract

Objectives: Toxocariasis is a zoonotic disease caused by Toxocara canis and T. cati. Human is their paratenic host. Although many clinico-epidemiological aspects have been studied in almost 60 years after the discovery of human disease, many biological and molecular aspects are still lack of knowledge and research. After a careful review of literature we did not found any study describing the phylogenetics of Toxocara using any molecular marker. Methods: For these reasons, nuclear internal transcribed spacer 2 (ITS2) rDNA sequences were used for the first molecular phylogenetic analysis and tree of five Toxocara species. ITS2 rDNA sequences were already available from GenBank (accession numbers AB110034, AB110033, EU189085, AM231609 and AB027152), corresponding to T. canis, T. cati, T. vitulorum, T. malaysiensis and T. tanuki. Phylogenetic analysis was made after aligned these sequences using GeneDoc 2.7, using the method of Maximum Parsimony and the bootstrap test for phylogeny with MEGA 4. Results: As expected, T. canis and T. cati ITS2 alleles are monophyletic, as well T. malaysiensis with T. vitulorum. As expected also, we observed a high nucleotide diversity (p = 0.705825; Tajima test = 0.461359) between the studied species Conclusions: The nuclear ITS rDNA sequence has been extensively used to define genetic markers for different species of nematodes and the aims of this study were to use the ITS2 to investigate the levels of genetic variation within Toxocara and generate a first phylogenetic tree. If there are normal levels of gene flow between populations (or species), these populations are likely to be similar in their overall genetic characteristics, and genes for important characteristics are likely to spread easily. ITS2 of other Toxocara species should be included in further analysis (eg. T. genettae, T. lyncis, T. vincenti, among others), to better define the evolutionary relationships and phylogeny of the genus Toxocara.