Non-archetypal Type II-like and atypical strains of Toxoplasma gondii infecting marsupials of Australia

Abstract

Australia is geographically isolated and possesses a remarkable diversity of wildlife species. Marsupials are highly susceptible to infection with the cosmopolitan parasite Toxoplasma gondii. Of 46 marsupials screened for T. gondii by multilocus PCR-DNA sequencing at polymorphic genes (B1, SAG3, GRA6, GRA7), 12 were PCR-positive; the majority (67%; 9/12) were infected by nonarchetypal Type II-like or atypical strains. Six novel alleles were detected at B1, indicating greater diversity of genotypes than previously envisaged. Two isolates lethal to marsupials, were avirulent to mice. The data support the conclusion that Australia’s isolation may have favoured the persistence of nonarchetypal ancestral genotypes.

Genetic characterisation of Toxoplasma gondii in wildlife from North America revealed widespread and high prevalence of the fourth clonal type

“…The archived strains from the three wallabys from Pennsylvania (Dubey and Crutehley, 2008) were classified as clonal Type III. Recently, Parameswaran et al (2010) characterised T. gondii DNA amplified directly from tissues of naturally-infected kangaroos in Australia and reported the presence of both archetypal Types I and II, and non-archetypal lineage alleles among strains circulating in Australian macropods. Of the 13 specimens PCR-positive with the B1 gene, DNA sequencing identified five with the type I allele, two with the type II or III allele, and seven had new alleles; viable T. gondii were not available for further genotyping.…”

“…Of the 13 specimens PCR-positive with the B1 gene, DNA sequencing identified five with the type I allele, two with the type II or III allele, and seven had new alleles; viable T. gondii were not available for further genotyping. Genotyping of two archived strains (one Macropus rufogriseus, one Vombatus ursinus) from tachyzoites grown in cell culture, revealed an atypical genotype (Parameswaran et al, 2010). Moré et al (2010) cultivated viable T. gondii from two macropods (Macropus rufus, Macropus giganteus) that had died in a zoo in Argentina.…”

The molecular epidemiology of parasite infections: Tools and applications

“…In Europe and North America, Toxoplasma gondii is considered to have a predominantly clonal population structure, with three main clonal lineages, referred to as Types I, II and III, accounting for >85% of strains isolated from humans and domestic animals [59]. However, recent studies of isolates of T. gondii in wildlife from North and South America, as well as Australia have uncovered more biological and genetic diversity [60,61,62]. Although some strains infecting wildlife appear to be recombinant genotypes derived from crosses between the archetypal clonal lineages, others are atypical strains which possess completely novel alleles.…”

“…Molecular epidemiological studies of threatened native wildlife in Western Australia have revealed the occurrence of mixed infections with T. gondii and Trypanosoma spp., which may be associated with the decline of Bettongia penicillata [173]. Mixed infections with different genotypes of T. gondii are common in Australian wildlife, but it is not yet known how this influences the virulence of infections [62].…”

“…The measure of virulence in all these studies was the mortality rate of mice challenged with a standard intra-peritoneal dose of parasites. Virulence, however, is not a static property of the genome of T. gondii and strains of the parasite that are highly virulent in one species of host may be completely avirulent in another host species [62]. From the point of view of the parasite, host species is an environmental factor that may markedly influence the phenotypic expression of virulence.…”