Sequence variation in the Toxoplasma gondii ROP20 gene among strains from different hosts and geographical locations.

Toxoplasma gondii, an opportunistic protozoan parasite, infects almost all warm-blooded animals. In this study, we examined the sequence variation in rhoptry protein 20 (ROP20) genes among 18 T. gondii isolates collected from different hosts and geographical regions. Full length ROP20 genes were amplified and sequenced. The results showed that the genes were 1659 bp in length and contained only a single exon, and that the A+T content varied from 46.68 to 47.20% among the 18 strains. The results of sequence alignment indicated that there were 30 variable nucleotide positions (0-1.40%) in the 18 T. gondii strains containing 18 transitions and 11 transversions, representing 1.81% overall sequence variation. Phylogenetic analysis of the ROP20 sequences showed that ROP20 variation could differentiate between the clonal lineage genotypes I and ToxoDB #9, indicating that ROP20 exhibits a relatively marked degree of sequence diversity and might represent a novel genetic marker for intraspecies phylogenetic analyses of T. gondii.

Seroprevalence, risk factors and genetic characterization of Toxoplasma gondii in free-range white yaks (Bos grunniens) in China.

The objective of this study was to determine the seroprevalence, risk factors and genotypes of Toxoplasma gondii in white yaks (Bos grunniens) in China. A total of 974 serum samples were collected from white yaks in Tianzhu Tibetan Autonomous County (TTAC), Gansu province, northwest China for detecting T. gondii antibodies by the modified agglutination test (MAT), and 414 tissues belonging to 138 white yaks were collected for detecting T. gondii DNA by amplification of B1 gene with a semi-nested PCR. A total of 155 serum samples (15.91%) were seropositive for T. gondii antibodies at a 1:100 cut-off, and 10 DNA samples (7.25%) were positive for the T. gondii B1 gene, which were genetically characterized using multilocus PCR-RFLP. Only one genotype (ToxoDB#9) was identified from two samples with complete genotyping results. Statistically significant differences were not observed between T. gondii seroprevalence and gender, season or pregnancy in the logistic regression analysis (P>0.05). Ages of white yaks was considered as a main risk factor associated with T. gondii infection. Our results indicated a widespread exposure to T. gondii among white yaks, and revealed the genotype ToxoDB#9 of T. gondii in white yaks for the first time in China.