Concomitant immunity to Schistosoma mansoni in mice.

OBJECTIVE The aim of the present study was to confirm observations on the concomitant immunity to Schistosoma mansoni in mice and assess its effects on the resistance of mice to a challenge infection. METHODS Cercariae from infected Biomphalaria glabrata were used to infect mice. Twenty mice were infected with a single dose of S. mansoni cercariae. The animals were randomly divided into two groups: experimental group (Group A) and control group (Group B). Group A mice were challenged with the same number of cercariae six weeks after the primary infection. Perfusion of all mice was done 9 weeks after infection in order to obtain worm burdens in relation to their initial cercarial dose. The livers of all mice were obtained for parasitological and pathological assessments. RESULTS Our results showed that all the exposed animals became infected with S. mansoni. After a challenge infection, Group A mice had a 54.66% worm reduction rate, 41.45% liver egg reduction rate, and 51.76% granuloma size reduction rate compared to their respective controls. This study shows that mice with persistent adult S. mansoni infection are able to mount a very strong regulatory response to a challenge infection. It is concluded that concomitant immunity does occur in mice. CONCLUSION These results describe novel imaging methods that permit visualization of live schistosomes within their living hosts and may help to elucidate mechanisms of infection and also be of value not only for epidemiological investigations, but also in designing government control programs for schistosomiasis.