Phylogeny and virulence divergency analyses of Toxoplasma gondii isolates from China

Abstract

BackgroundToxoplasma gondii (T. gondii) is a very successful parasite that can infect virtually all warm blooded animals with a worldwide distribution. It causes a large range of clinical manifestations in both humans and domesticated animals. In addition, marked biological differences exist among T. gondii strains in the pathogenicity and geographical distribution. Molecular epidemiology studies primarily based on restriction fragment length polymorphism (RFLP) method revealed that three main types are predominant in North America and Europe, whereas other diverse genotypes are found in other parts of the world. Microsatellite (MS) as a type of genetic marker has been widely used in many organisms. Limited MS genotyping, however, to fingerprint T. gondii isolates has been reported and little is known about the MS data of the strains predominantly prevalent in China.MethodsGenotyping of twenty-eight Chinese T. gondii isolates were performed using 15 MS markers located on 12 different chromosomes. Results were analyzed in terms of population structure by a Bayesian statistical approach. Phylogenetic analysis was obtained from a Neighbor-Net phylogenetic network. The virulence analyses of some representative isolates were determined by inoculation of mice and cell invasion assays. The gene expressions of some virulence-associated factors (VFs) were performed by quantitative real-time PCR (qRT- PCR).ResultsThree haplogroups were clustered among the 28 isolates although minor genetic differences were found within haplogroups. The majority of strains belong to one haplogroup corresponding to the previously described Chinese 1 type (ToxoDB#9). Phylogenetic networks uncovered a limited diversity of T. gondii strains and the virulence differs in the strains sharing the same genotype. No remarkable difference, however, was noted in the tested VFs except for dense granule protein3 (GRA3), which was found to have a higher expression in low virulent TgCtwh6 (Wh6) strain than that in high virulent TgCtwh3 (Wh3) strain.ConclusionThe profile of microsatellite typing data from Chinese T. gondii strains revealed a limited genetic diversity and the selected VFs and phylogenetic network analyses displayed less divergence, although the strain virulence differs in the Chinese 1 type of T. gondii predominantly prevalent in China.

Identification of a TNF-α inducer MIC3 originating from the microneme of non-cystogenic, virulent Toxoplasma gondii

“…The ratio of TNF-α produced in response to RH and TgCtwh3 was approximately 3-fold, and RH produced significantly more TNF-α than TgCtwh3 ( P  < 0.001). Therefore, the reported T. gondii dose-dependent hazard ratio3 and the level of TNF-α production seemed to be correlated ( r  > 0.6, P  < 0.05). In addition, we assessed the parasite burden in the spleens of infected mice.…”

“…The virulence of the RH and TgCtwh3 strains has been studied by measuring the survival times of mice inoculated with T. gondii tachyzoites3. However, differences in the host immune responses to these strains have not yet been evaluated.…”

“…found that the average number of survival days post-infection of mice with 10 tachyzoites was 9 days for strain RH and 12 days for strain TgCtwh3. The dose-dependent hazard ratio for mice infected with RH tachyzoites was more than 3-fold higher than that with TgCtwh3 tachyzoites3. However, the underlying molecular reasons for this discrepancy are unclear.…”

“…The RH strain (Type I genotype) is a common virulent isolate in North America and Europe, and strain TgCtwh3 (Chinese 1 genotype) is common in China23. Previous studies have demonstrated that strain TgCtwh3 is less virulent than strain RH.…”

“…Previous studies have demonstrated that strain TgCtwh3 is less virulent than strain RH. For example, Li et al 3. found that the average number of survival days post-infection of mice with 10 tachyzoites was 9 days for strain RH and 12 days for strain TgCtwh3.…”