Development of vaccines against Toxoplasma gondii
infection in humans is of high priority, given the high burden
of disease in some areas of the world like South America, and the lack of effective drugs with few adverse effects.
Rodent models have been used in research on vaccines against T. gondii
over the past decades. However, regardless
of the vaccine construct, the vaccines have not been able to induce protective immunity when the organism is
challenged with T. gondii
, either directly or via a vector. Only a few live, attenuated T. gondii
strains used for immunization
have been able to confer protective immunity, which is measured by a lack of tissue cysts after challenge.
Furthermore, challenge with low virulence strains, especially strains with genotype II, will probably be insufficient
to provide protection against the more virulent T. gondii
strains, such as those with genotypes I or II, or those genotypes
from South America not belonging to genotype I, II or III. Future studies should use animal models besides
rodents, and challenges should be performed with at least one genotype II T. gondii
and one of the more virulent
genotypes. Endpoints like maternal-foetal transmission and prevention of eye disease are important in addition to
the traditional endpoint of survival or reduction in numbers of brain cysts after challenge.