Geographic Separation of Domestic and Wild Strains of Toxoplasma gondii in French Guiana Correlates with a Monomorphic Version of Chromosome1a

Abstract

BackgroundPrevious studies have stressed the genetic divergence and high pathogenicity of strains of T. gondii from French Guiana. Although strains from coastal, human adapted environments (so called anthropized) resemble those found in other regions of the Caribbean, strains collected from inland jungle environment are genetically quite diverse. To better understand the composition of these distinct strain types, we undertook a more in depth analysis of T. gondii strains from French Guiana including profiling of chromosome 1a (Chr1a), which is often shared as a single monomorphic haplotype among lineages that are otherwise genetically distinct.Methodology/Principal FindingsComparison of intron sequences from selectively neutral genes indicated that anthropized strains were most closely related to clonal type III strains from North America, although wider RFLP analysis revealed that they are natural hybrids. In contrast, strains isolated from the jungle were genetically very diverse. Remarkably, nearly all anthropized strains contained the monomorphic version of Chr1a while wild stains were extremely divergent. The presence of the monomorphic Chr1a strongly correlated with greater transmission in domestic cats, although there were several exceptions, indicating that other factors also contribute. Anthropized strains also varied in their virulence in laboratory mice, and this pattern could not be explained by the simple combination of previously identified virulence factors, indicating that other genetic determinants influence pathogenicity.Conclusions/SignificanceOur studies underscore the marked genetic separation of anthropized and wild strains of T. gondii in French Guiana and provide additional evidence that the presence of Chr1a is associated with successful expansion of widely different lineages within diverse geographic areas. The predominance of Chr1a among strains in the anthropized environment suggests that it may confer an advantage for transmission in this environment, and thus potentially contribute to the spread of pathogenecity determinants.

Genetic Mapping of Pathogenesis Determinants inToxoplasma gondii

“…Although type 3 strains are avirulent in mice, type 9 strains like P89 show high levels of acute virulence in laboratory mice (39), suggesting there are other determinants that mediate pathogenicity. Additionally, the patterns described here do not explain the phenotype of some natural recombinant strains, such as those isolated in French Guiana (55) or those in wildlife from North America (29), where known virulence determinants do not correlate with mouse virulence. Additionally, the virulence traits of many of the major lineages (i.e., types 13 from China, 14 from Africa, 16 from Europe, and 11 from North America) have not been examined experimentally, and they may rely on other determinants.…”

“…Recent studies suggest that strains harboring the monomorphic Chr1a * are better adapted for transmission in domestic cats, whereas those with divergent versions of Chr1a are deficient in self-mating in domestic cats (55). In both Most recent common ancestry (MRCA): an estimate derived from assumptions about the neutral mutation rate and the accumulated rate of drift Monomorphic: characteristic of a genomic region that is highly similar between two or more strain types as compared to the rest of the genome; based on polymorphism rates Admixture: patterns of genetic mixing that result from recombination between formerly separated or different populations in the wild North and South America, more divergent strains are common among wild animals, whereas clonal strains inhabit environments altered by human activity, suggesting that there are separate domestic and sylvatic cycles of transmission (55,57,77). Such patterns have implications for the spread of genes between populations, including those that influence pathogenesis, as considered further below.…”

Analysis of Noncanonical Calcium-Dependent Protein Kinases in Toxoplasma gondii by Targeted Gene Deletion Using CRISPR/Cas9

“…The wild-type RH strain (referred to as RH88 in reference 31), previously described mutants that are defective in nonhomologous end joining RH⌬ku80 (32) and Pru⌬ku80 (33), and genetically modified strains generated here were grown in confluent monolayers of human foreskin fibroblast (HFF) cells in D10 medium composed of Dulbecco's modified Eagle medium (DMEM), 10% fetal bovine serum (FBS) (HyClone) 2 mM glutamine (Sigma), 10 mM HEPES, pH 7.5 (Sigma), and 20 g/ml gentamicin maintained at 37°C with 5% CO 2 . Parasites were allowed to egress naturally, harvested by filtration through 3.0-m polycarbonate membranes, and resuspended in Hanks' balanced salt solution (HBSS) containing 10 mM HEPES and 0.1 mM EGTA (referred to as HHE) as described previously (34). All strains and host cell lines were determined to be mycoplasma negative using the e-Myco plus kit (Intron Biotechnology).…”

“…in a volume of 200 l of HHE containing 1,000 parasites per animal in 8-to 10-week-old C57BL/6 mice (Jackson Laboratories). Mice were monitored for survival daily, and surviving animals were tested serologically by enzyme-linked immunosorbent assay (ELISA) to establish that they were infected, as described previously (34). Cyst counting was performed as described previously (39).…”

Parasites: Kitty carriers

“…Highly virulent strains that can cause severe illness and even death in healthy adults have been identified in the jungle ecosystems of French Guiana -areas that are separated from densely populated regions only by a porous and fragile ecological barrier 3 . For these reasons, scientists are trying to understand why T. gondii is so widespread and how it moves through today's environment.…”