الفهرس 
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Abstract
Toxoplasma gondii (T. gondii) is an important apicomplexan parasite which is globally affecting around one third of the world’s population. Infection is usually asymptomatic in the immunocompetent people, or it can be associated with a mild, self-limited disease with or without lymphadenopathy. Besides, in immunocompromised and congenitally-infected individuals, it causes severe life-threatening illness.
Chemotherapy for human and animals T. gondii infection is based on synergistic combination of pyrimethamine and sulfadiazine that disrupts the biosynthesis of folic acid and represents the common primary control measure. However, the treatment regimens are highly effective against the rapidly dividing tachyzoite stage in the acute infection, with no significant activity against the encysted bradyzoites, and are unable to cure persistent infections. Besides, these compounds cause many side-effects and cannot prevent the infection.
Therefore, there is an urgent need for an effective vaccine discovery, as an alternative control and preventive tool against toxoplasmosis. The only available commercial vaccine “Toxovax” is based on live attenuated S48 strain and has been licensed for usage to avoid congenital infection in sheep and goat. However, this vaccine is not suitable for humans, as it may change to a pathogenic strain. Additionally, it is expensive, has adverse effects, and has a short shelf-life. Thus, currently no licensed vaccine available for humans. In order to solve this problem, numerous vaccination trials against toxoplasmosis have been performed experimentally during the past two decades using different vaccine types with various strategies, including inactivated killed vaccine, live attenuated vaccine, genetically engineered vaccine and DNA vaccine with promising results.
It was noted that vaccination with single antigen related to a specific stage in the life cycle leads to stage-limited protection against T. gondii. Thus, it is essential to develop multiantigenic vaccines related with different growth stages in the parasite life cycle.