Review of Toxoplasmosis: What We Still Need to Do

Toxoplasma gondii is responsible for the disease toxoplasmosis and has the broadest host range among apicomplexan parasites, as it infects virtually all warm-blooded vertebrates. Toxoplasmosis is a zoonotic and emerging public health concern with considerable morbidity and mortality, especially in the developing world, affecting approximately one-third of the world's human population. Clinical presentation varies among species, and the infection establishes lifelong chronicity in hosts. Most of the host species (including healthy humans) are asymptomatic on the one hand, it is fatal to marsupials, neotropical primates and some marine mammals on the other hand. In immunocompetent humans, infection is typically asymptomatic, whereas immunocompromised individuals may develop disseminated disease affecting virtually any organ system-most commonly reproductive, cerebral, and ocular systems. Toxoplasmosis spreads by ingestion of food or water contaminated with T. gondii oocysts, consumption of undercooked/raw meat containing tissue cysts, transplacental transmission from mother to fetus, or by receiving infected organ/blood from the infected individual. Toxoplasmosis is mainly diagnosed by serologic tests and polymerase chain reaction (PCR). It is treated with pyrimethamine combined with sulfadiazine or clindamycin, often supplemented with leucovorin, atovaquone, and dexamethasone. Despite having many potent anti-T. gondii antigenic candidates, there is no commercially available vaccine for humans due to many factors, including the complex life cycle of the parasite and its evasion strategies. To date, the only commercially available anti-T. gondii vaccine is for sheep, licensed for veterinary use to prevent ovine abortions. In this review, we have summarized the current understanding of toxoplasmosis.