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A great deal of evidence demonstrates that a strongly clonal population structure of Toxoplasma gondii strains exists in humans and animals in North America and Europe, while the strains from South America are genetically separate and more diverse. Potential differences in virulence between different strains mean that an understanding of strain diversity is important to human and animal health. However, to date, only one predominant genotype, ToxoDB#9 (Chinese I), and a few other genotypes, including ToxoDB#205, have been identified in China. By using DNA sequence-based phylogenetic analyses, we have re-evaluated the population structure of T. gondii strains collected from China and compared them with other global strains. Based on phylogenetic analysis of restriction fragment length polymorphisms, multilocus sequence typing and intron sequences from T. gondii, we propose that the Chinese isolates described as Chinese I are divided into two groups called Chinese I and Chinese III. Our results demonstrate that significant differences were found in mouse mortality caused by some Chinese strains, and also the archetypal I, II, III strains in mice. Furthermore, a comparison of cyst loading in the brains of infected rats showed some Chinese strains to be capable of a high degree of cyst formation. Furthermore we show that genotyping using neutral genetic markers may not be a useful predictor of pathogenic phenotypes., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Toxoplasma gondii is a globally distributed parasite infecting humans and warm-blooded animals. Although many surveys have been conducted for T. gondii infection in mammals, little is known about the detailed distribution in localized natural populations. In this study, host genotype and spatial location were investigated in relation to T. gondii infection. Wood mice (Apodemus sylvaticus) were collected from 4 sampling sites within a localized peri-aquatic woodland ecosystem. Mice were genotyped using standard A. sylvaticus microsatellite markers and T. gondii was detected using 4 specific PCR-based markers: SAG1, SAG2, SAG3 and GRA6 directly from infected tissue. Of 126 wood mice collected, 44 samples were positive giving an infection rate of 34.92% (95% CI: 27.14-43.59%). Juvenile, young adults and adults were infected at a similar prevalence, respectively, 7/17 (41.18%), 27/65 (41.54%) and 10/44 (22.72%) with no significant age-prevalence effect (P = 0.23). Results of genetic analysis of the mice showed that the collection consists of 4 genetically distinct populations. There was a significant difference in T. gondii prevalence in the different genotypically derived mouse populations (P = 0.035) but not between geographically defined populations (P = 0.29). These data point to either a host genetic/family influence on parasite infection or to parasite vertical transmission.

Myeloid differentiation factor 88 (MyD88)-dependent IL-12 secretion by dendritic cells is critical for natural killer cell-mediated IFN-γ production and innate resistance to Toxoplasma gondii. Although MyD88(-/-) mice challenged with T. gondii have defective IL-12 responses and succumb to infection, administration of IL-12 to MyD88(-/-) mice fails to prevent acute mortality, suggesting that MyD88 may mediate signals within natural killer cells important for IL-12-dependent IFN-γ production and innate resistance to this parasite. In this study, we found that T. gondii antigens and IL-12 could synergistically trigger IFN-γ secretion by natural killer cells, which was dependent on toll-like receptor-MyD88 signaling. Further analysis showed that p38 mitogen-activated protein kinase, extracellular signal-regulated kinase, c-Jun N-terminal kinase and NF-κB multiple pathways downstream of MyD88 contributed to IFN-γ production by natural killer cells. Moreover, the well-established toll-like receptor agonists, T. gondii profilin (Tgprofilin) and T. gondii heat shock protein 70 (TgHSP70) could evoke a similar IFN-γ secretory response in natural killer cells to that evoked by T. gondii antigens. In vivo adoptive transfer experiments showed that, upon challenge with T. gondii, NOD/SCID-β2 microglobulin null (NOD/SCID-β2m(-/-)) mice injected i.v. with MyD88(-/-) natural killer cells had reduced serum IFN-γ levels and increased splenic tachyzoite burdens compared with those injected i.v. with wild-type natural killer cells. Taken together, these findings demonstrate a critical role for natural killer cell intrinsic toll-like receptor-MyD88 signaling in IL-12-dependent early IFN-γ production and innate resistance to T. gondii., (Copyright © 2014 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.)

Fourteen isolates of Toxoplasma gondii were isolated from cats from 4 different geographic provinces (Anhui, Hubei, Shanxi and Guangdong) in China and their genetic diversity with 8 nuclear loci SAG2, SAG3, BTUB, GRA6, L358, PK1, c22-8, c29-2, and an apicoplast locus Apico, was analysed by restriction fragment length polymorphisms (RFLPs). Two genotypes from these 14 isolates were identified but none of them belongs to the typical genetic types (types I, II and III). It is unexpected that such high similarity was observed in these 14 isolates although their original regions are significantly distant. Our results strongly indicate that the three traditional clonal lineages of types I, II and III of this parasite may not be preponderant in China. In addition, our results show that the genotypes of T. gondii in China may be highly clonal with atypical genotypes and higher virulence., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The protozoan parasite Toxoplasma gondii is prevalent worldwide and can infect a remarkably wide range of hosts despite felids being the only definitive host. As cats play a major role in transmission to secondary mammalian hosts, the interaction between cats and these hosts should be a major factor determining final prevalence in the secondary host. This study investigates the prevalence of T. gondii in a natural population of Apodemus sylvaticus collected from an area with low cat density (<2·5 cats/km2). A surprisingly high prevalence of 40·78% (95% CI: 34·07%-47·79%) was observed despite this. A comparable level of prevalence was observed in a previously published study using the same approaches where a prevalence of 59% (95% CI: 50·13%-67·87%) was observed in a natural population of Mus domesticus from an area with high cat density (>500 cats/km2). Detection of infected foetuses from pregnant dams in both populations suggests that congenital transmission may enable persistence of infection in the absence of cats. The prevalences of the related parasite, Neospora caninum were found to be low in both populations (A. sylvaticus: 3·39% (95% CI: 0·12%-6·66%); M. domesticus: 3·08% (95% CI: 0·11%-6·05%)). These results suggest that cat density may have a lower than expected effect on final prevalence in these ecosystems.

The prevalence of anti-Toxoplasma gondii specific IgG in stray and household cats in Guangzhou, China was determined by ELISA on serum samples from 206 cats (117 strays and 89 households) and the overall infection rate was 25.24%. The infection rate in stray cats (30.77%) was significantly higher (P < 0.05) than in household cats (17.98%). The rate of infection between male and female cats of both groups was not significantly different (P > or = 0.05), 28.13% versus 32.61% for male and female in stray cats, respectively, and 18% versus 17.95% in household cats. The present investigation demonstrated that the prevalence of T. gondii infection in cats in Guangzhou was high, especially in stray cats, which are probably the main source of T. gondii infection in this area. Integrated control strategies and measures should be implemented to prevent and control T. gondii infection in both stray and household cats, which will have significant implications for the control of human infection with T. gondii.