MOLECULAR SYSTEMATICS AND COMPARATIVE POPULATION GENETICS OF PARASITIC ORGANISMS THAT THREATEN FOOD SAFETY AND SECURITY
Title: Genetic analyses of atypical Toxoplasma gondii strains reveals a fourth clonal lineage in North America
Submitted to: International Journal for Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 2, 2011
Publication Date: April 1, 2011
Citation: Khan, A., Dubey, J.P., Su, C., Ajioka, J.W., Rosenthal, B.M., Sibley, L.D. 2011. Genetic analyses of atypical Toxoplasma gondii strains reveals a fourth clonal lineage in North America. International Journal for Parasitology. 41:645-655.
Interpretive Summary: Three major lineages of the zoonotic foodborne parasite Toxoplasma gondii have been repeatedly encountered in people and in various other animals. Of late, sampling in certain wild animals have identified additional diversity. Here, we described and applied criteria to understand how these new isolates relate to each other, and to previously known types of this parasite. Doing so has enabled us to identify and describe a fourth major lineage of T. gondii in the USA.
Here we examined an expanded set of strains using sequenced-based
phylogenetic and population analyses to re-evaluate the population structure of T. gondii in North America. Our findings reveal that strains previous defined by atypical RFLP patterns fall into two
discrete groups. In one case, these new isolates represent variants of an existing lineage, from which they differ only by minor mutational drift. However, in a second case, it is evident that these strains define a completely new lineage that is common in North America. Support for this new lineage was based on phylogeny, principle components analysis, STRUCTURE analyses, and statistical analysis of gene flow between groups. This new group, referred to as haplogroup 12, contains divergent genotypes previously referred to as A and X, isolated from sea otters. Consistent with this, group 12 was found primarily in wild animals, as well as occasionally in humans. This new lineage also has a highly clonal population structure. Analysis of the inheritance of multilocus genotypes revealed that different strains within group 12 are the products of a single recombination event in the wild between type 2 and a unique parental lineage. Collectively, the archetypal type 2 has been associated with
clonal expansion of a small number of lineages in the North, as a consequence of separate but infrequent recombination with several different parental lines.