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.

Background: Toxoplasmosis, caused by an obligate intracellular protozoan parasite Toxoplasma gondii, has been a serious clinical and veterinary problem. Effective DNA vaccines against T. gondii can prevent and control the spread of toxoplasmosis, which is important for both human health and the farming industry. The T. gondii 14-3-3 protein has been proved to be antigenic and immunogenic and was a potential vaccine candidate against toxoplasmosis. In this study, we evaluated the immune responses induced by recombinant plasmids encoding T. gondii surface antigen 1 (SAG1) and 14-3-3 protein by immunizing BALB/c mice intramuscularly. Methods: In the present study, BALB/c mice were randomly divided into five groups, including three experimental groups (pSAG1, p14-3-3 and pSAG1/14-3-3) and two control groups (PBS and pBudCE4.1), and were immunized intramuscularly three times. The levels of IgG antibodies and cytokine production in mouse sera were determined by enzyme-linked immunosorbent assays (ELISA). Two weeks after the last immunization, all mice were challenged intraperitoneally (i.p.) with 1×10⁴ tachyzoites of T. gondii and the survival time of mice was observed and recorded every day. Results: Mice vaccinated with pSAG1, p14-3-3 or pSAG1/14-3-3 developed high levels of IgG2a and gamma interferon (IFN-γ) and low levels of interleukin-4 (IL-4) and interleukin-10 (IL-10) compared to control groups (PBS or pBudCE4.1), which suggested a modulated Th1 type immune response (P<0.05). After intraperitoneal challenge with 1×10⁴ tachyzoites of T. gondii (RH strain), the survival time of mice in experimental groups was longer than control groups (P<0.05). Mouse immunized with pSAG1/14-3-3 induced a higher level of IgG antibody response and significantly prolonged the survival time when compared with pSAG1 or p14-3-3 (P<0.05). Conclusions: The study suggested that T. gondii 14-3-3 protein can induce effective immune responses in BALB/c mice and was a novel DNA vaccine candidate against toxoplasmosis, and the immune protective efficacy elicited by SAG1 gene was also demonstrated. Our results also showed multi-gene vaccine significantly enhanced immune responses and protective efficacy and was superior to the single-gene vaccine.