Xing-Quan Zhu

Globally diverse Toxoplasma gondii isolates comprise six major clades originating from a small number of distinct ancestral lineages

Marked phenotypic variation characterizes isolates of Toxoplasma gondii, a ubiquitous zoonotic parasite that serves as an important experimental model for studying apicomplexan parasites. Progress in identifying the heritable basis for clinically and epidemiologically significant differences requires a robust system for describing and interpreting evolutionary subdivisions in this prevalent pathogen. To develop such a system, we have examined more than 950 isolates collected from around the world and genotyped them using three independent sets of polymorphic DNA markers, sampling 30 loci distributed across all nuclear chromosomes as well as the plastid genome. Our studies reveal a biphasic pattern consisting of regions in the Northern Hemisphere where a few, highly clonal and abundant lineages predominate; elsewhere, and especially in portions of South America are characterized by a diverse assemblage of less common genotypes that show greater evidence of recombination. Clustering methods were used to organize the marked genetic diversity of 138 unique genotypes into 15 haplogroups that collectively define six major clades. Analysis of gene flow indicates that a small number of ancestral lineages gave rise to the existing diversity through a process of limited admixture. Identification of reference strains for these major groups should facilitate future studies on comparative genomics and identification of genes that control important biological phenotypes including pathogenesis and transmission.

Toxoplasma gondii infection in humans in China

Toxoplasmosis is a zoonotic infection of humans and animals, caused by the opportunistic protozoan Toxoplasma gondii, a parasite belonging to the phylum Apicomplexa. Infection in pregnant women may lead to abortion, stillbirth or other serious consequences in newborns. Infection in immunocompromised patients can be fatal if not treated. On average, one third of people are chronically infected worldwide. Although very limited information from China has been published in the English journals, T. gondii infection is actually a significant human health problem in China. In the present article, we reviewed the clinical features, transmission, prevalence of T. gondii infection in humans in China, and summarized genetic characterizations of reported T. gondii isolates. Educating the public about the risks associated with unhealthy food and life style habits, tracking serological examinations to special populations, and measures to strengthen food and occupational safety are discussed.

Genetic characterization of Toxoplasma gondii isolates from China

Toxoplasma gondii infections are prevalent in humans and animals worldwide. In North America and Europe, T. gondii is highly clonal, consisting of three distinct lineages (Types I, II and III), whereas in South America, T. gondii is highly diverse with a few lineages expanded in the population. However, there is limited data on the diversity of T. gondii in Asia. Here we report the genetic characterization of T. gondii isolates from different hosts and geographical locations in China using the multilocus PCR-RFLP. A total of 17 T. gondii isolates from humans (3 strains), sheep (1 strain), pigs (5 strains) and cats (8 strains) were typed at 10 genetic markers including 9 nuclear loci SAG1, SAG2, SAG3, BTUB, GRA6, L358, PK1, c22-8, c29-2 and an apicoplast locus Apico. Four genotypes were revealed, including three previously reported and one new genotype. Three isolates belong to the clonal Type I lineage, one isolate belongs to the clonal Type II lineage, and the rest 13 isolates are grouped into two genotypes. This is the first report of genetic typing of T. gondii isolates from different hosts and geographical locations in China using a number of genetic markers, which has implications for the studies of population genetic structures of T. gondii, as well as for the prevention and control of T. gondii infections in humans and animals in China.

Seroprevalence of Toxoplasma gondii in pigs in Southwestern China.

The seroprevalence of toxoplasmosis in pigs was investigated in Yunnan province, Southwestern China between March 2008 and January 2009. A total of 831 serum samples were collected from 9 counties and assayed for Toxoplasma gondii antibodies by indirect haemagglutination (IHA) test. Antibodies to T. gondii were found in 16.97% (141/831) with slaughter pigs having the highest rate (22.28%), followed by breeding sows (16.59%). The results of the present survey indicated that infection with T. gondii in pigs is widely spread in China, including the Yunnan province, and is of public health concern.

First Report of Genotyping of Toxoplasma gondii Isolates From Wild Birds in China

Abstract: Toxoplasma gondii is an important cosmopolitan opportunistic protozoan parasite, which threatens the health of human beings and animals. Genetic characterization of isolates from South America has revealed high genetic diversity. In contrast, isolates from North America and Europe were highly clonal, with 3 major lineages known as the Types I, II, and III. However, limited information on T. gondii genotypes has been reported in The Peoples Republic of China. Here we conducted a survey to determine genetic diversity of this parasite in wild birds of China. In total, tissues from breast muscle of 178 wild birds, including 98 common pheasants (Phasianus colchicus), 35 tree sparrows (Passer montanus), 22 house sparrows (Passer domesticus), 20 saxaul sparrows (Passer ammodendri), and 1 cinnamon sparrow (Passer rutilans), were tested for T. gondii infection, 4 of which were found to be positive for the T. gondii B1 gene by PCR amplification. These positive DNA samples were typed at 10 genetic markers, including 9 nuclear loci, i.e., SAG1, 5′- and 3′-SAG2, alternative SAG2, SAG3, GRA6, L358, PK1, c22-8, c29-2, and an apicoplast locus Apico. Of these, 3 isolates were genotyped with complete data for all loci, and 2 genotypes (Type I and Type II variant) were identified. This is the first report of genetic typing of T. gondii isolates from wild birds from different regions in China. The results suggest that the Type I and II variant strains are circulating in wild birds in China, and these birds are potential reservoirs for T. gondii transmission.

Antibodies to Toxoplasma gondii in Stray and Household Dogs in Guangzhou, China

Abstract The frequency of Toxoplasma gondii antibodies in stray and household dogs in Guangzhou, China was examined by ELISA on serum samples from 150 animals (36 strays and 114 from households) and the overall prevalence was 21.3%. The extent of infection in stray dogs (33.3%) was significantly higher (P < 0.05) than in household dogs (17.5%). Infection in male and female dogs of both groups was not significantly different (P ≥ 0.05), i.e., 31.8% versus 35.7% for male and female in stray dogs, and 14.5% versus 22.2% in household dogs. The results of the present investigation indicate that the seroprevalence of T. gondii infection in dogs was high in Guangzhou, especially in strays. Therefore, it is essential to implement integrated strategies to prevent and control T. gondii infection in both stray and household dogs.

Seroprevalence of Toxoplasma Gondii in Pigs From Southern China

Abstract The seroprevalence of toxoplasmosis in pigs was examined in Chinas southern Guangdong Province from March 2008 through May 2009. A total of 1,022 serum samples was collected from 12 administrative cities and assayed for Toxoplasma gondii antibodies by enzyme-linked immunosorbent assay test. The seroprevalence ranged from 0 to 58.1% and the average T. gondii antibody-positive prevalence was 27.0% (276/1,022), with breeding boars having the highest level at 39.6% (38/96) followed by breeding sows at 36.9% (52/141). The results of the present survey indicate that T. gondii infection is a significant health problem in pigs and represents a public health concern in southern China.

Seroprevalence of Toxoplasma gondii Infection in Tibetan Sheep in Tibet, China

Abstract In the present investigation, the seroprevalence of Toxoplasma gondii antibodies in 455 Tibetan sheep in Tibet, China, was examined using an indirect hemagglutination test. Of these, 26 (5.7%) Tibetan sheep were seropositive at the cut-off of 1:64 serum dilution. The seroprevalence ranged from 2.2% to 8.9% among Tibetan sheep of <1-yr-old, 1–3-yr-old, and >3-yr-old, but the differences among the age groups were not significant (P > 0.05). The prevalence in male Tibetan sheep (2.8%) was lower than that in female Tibetan sheep (6.6%), but the difference was not statistically significant (P > 0.05). The results of this survey indicated the presence of T. gondii infection in Tibetan sheep, which may cause economic losses to the local livestock industry and which poses a potential threat to human health in this area.

Seroprevalence of Neospora caninum Infection in Dairy Cattle of Southern China

Abstract A seroepidemiological survey of Neospora caninum infection in dairy cattle was carried out in Chinas southern Guangdong Province between July 2009 and March 2010. A total of 370 serum samples of dairy cattle was collected from 5 farms and examined for antibodies to N. caninum by enzyme-linked immunosorbent assay. The overall seroprevalence of N. caninum in dairy cattle was 18.9% (70/370). The seroprevalence of N. caninum in aborting cows (22.7%) was higher than that in nonaborting cows (16.3%), but the difference was not statistically significant (P > 0.05). Five-yr-old dairy cattle had the highest seroprevalence (27.8%), followed by those that were 6-yr-old (20.4%). Dairy cattle with 4 pregnancies had the highest seroprevalence (29.2%). There was no apparent association of N. caninum seropositivity with age or number of pregnancies (P > 0.05). The results of the present survey indicated that the infection with N. caninum is prevalent in dairy cattle of all ages in southern China, which may be one of the causes of bovine abortion. This is the first report of seroprevalence of N. caninum in dairy cattle in southern China.

Seroprevalence of Toxoplasma gondii in Bred Cynomolgus Monkeys (Macaca fascicularis) in China

Abstract Little is known of the seroprevalence of Toxoplasma gondii in bred cynomolgus monkeys (Macaca fascicularis) in China. In the present survey, 240 serum samples of cynomolgus monkeys from 4 nonhuman primate centers in Guangxi Zhuang Nationality Autonomous Region (GX), and 120 serum samples from 2 nonhuman primate centers in Guangdong Province (GD) were obtained, and the modified agglutination test (MAT) was performed to assay for anti–T. gondii antibodies. Antibodies to T. gondii (MAT titer of 1∶16 or higher) were found in 0 of 120 (0/120) samples in GD, and 5 (2.1%) of 240 sera with titers of 1∶16 in 1, 1∶64 or higher in 4 in primate centers from GX. The total prevalence of T. gondii in bred cynomolgus monkeys was 1.4% (5/360, MAT titer ≥ 1∶16) in southern China according to our investigation. To our knowledge, this is the first seropositive report in China on the prevalence of anti–T. gondii antibodies in bred cynomolgus monkeys using MAT.