Chronic infection with Toxoplasma gondii does not prevent acute disease after virulent strain reinfection in experimental mice

Abstract

Background: Toxoplasmosis is a wide spread protozoan disease. It was generally believed that primary infection by T. gondii protects from reinfection, however, multiple cases of reinfection have been detected in immune mothers. This work reports results of re-infection of Swiss Webster (SW) mice with different strains of T. gondii. Objective: To simulate the impact of reinfection in experimentally infected mice with lethal strain of T. gondii after prime infection with non-virulent genotype. Methodology: The study was conducted on 36 female SW mice which were divided into four groups: 6 mice were infected with ME49 only (GI); 18 mice were infected with ME49 and re-challenged with RH on day 65, i.e. 8 weeks post ME49 infection (GII); 6 mice were infected with RH only (GIII); and 6 non-infected control mice (G1V). Toxoplasma RH strain re-challenged mice (GII) were monitored over two weeks observation period for mortality, clinical signs of acute illness (scoredgradesI-II), presence of intraperitoneal tachyzoites, brain cyst burden, and compared to chronically infected non-challenged mice (GI) and mice infected with RH only (GIII). Results: Prolonged survival rate of re-challenged group of mice thanin RH only infected group was the only significant result. Cyst number and diameter were higher in re-challenged group than in mice infected only with ME49. Tachyzoites were recovered from peritoneal lavage of all mice that received RH whether primarily infected with ME49 or not. Clinical grading (I-II) was the same for both groups and both reached grade II. Conclusion: These results highlighted that mice with chronic toxoplasmosis developed acute disease when re-challenged with another virulent strain. Therefore,chronic infection with T. gondii apparently neither prevents acute disease nor impairs colonization of the brain with tissue cysts after virulent strain superinfection. The present work supports and explains the possibility of congenital toxoplasmosis in immune pregnant mothers when re-infected by a virulent strain of T. gondii.