Schistosoma mansoni: reinfections and concomitant immunity in mice: importance of perfusion time after challenge infection for evaluation of immunoprotection

Abstract

The concomitant immunity in the presence of repeated infections (with 15 cercariae) was studied in mice sacrificed on the 20th day after each infection. The comparison of the averages of immature worms, recovered from mice submitted to reinfection, with those of their respective controls (previously uninfected) showed a significantly lower worm recovery rate in the animals with previous infections (concomitant immunity). However, statistically significant differences could not be detected among the various groups of animals, when the mice that accumulated worms in this mature stage were perfused. The theoretical projection based on the accumulation of young worms which developed to adult ones indicates a lower recovery rate of adult worms in the animals with concomitant immunity, but this projection was not corroborated by the experimental data. The visceral hemodynamic alterations that occurred in reinfections due to the pathogeny, favouring recirculation of the recent arriving worms to the portal system, could explain the lower recovery rate of immature worms, which could remain in other organs on the occasion of perfusion of the portal system. These results suggest that special care should be taken when one wants to investigate concomitant immunity in mice based on the distinction of the immature worms from challenge infection and the mature ones from primary infection.

Influence of pattern of exposure, parasite genetic diversity and sex on the degree of protection against reinfection with Schistosoma mansoni

“…Most studies concerned monkeys where both unisexual male trickle infection (Vogel and Minning 1953) and bisexual trickle infection (Webbe and James 1973;Cheever and Duvall 1974;Damian et al 1981;Sturrock et al 1984;Reid et al 1995;Farah et al 1997) induced a convincing protective effect to a bisexual challenge. Trickle infections on mice also induced a convincing protective effect but only concerned repeated bisexual infections (el-Garem et al 1970;Moloney et al 1984;Andrade and Mauadie de Azevedo 1987;Lewis et al 1987;Coelho et al 1995). The protective effect of unisexual male or female trickle infections on mice has never been tested.…”

Synergistic action of praziquantel and host specific immune response against Schistosoma mansoni at different phases of infection

“…In concomitant immunity a part of reduction in worm burden from reinfection would be due to recirculation of juvenile worms -that at the moment of perfusion would be in other sites of the organism (mainly in the lungs) and, therefore, would not be taken into account for statistical estimationthan to a true protective immunity. Juvenile worm recirculation would occur through porto-cava shunts resulting from portal hypertension typical of the disease 2,13 . To achieve 50% worm burden reduction in mice treated at 28 days after reinfection, it was necessary to use 1000 mg kg -1 PZQ, a higher PZQ concentration than that required for an effective therapeutic dose (data not shown).…”

Evaluation of an antigen-ELISA in the diagnosis of bovine cysticercosis in Kenyan cattle

“…The low sensitivity of the assay in artificially infested calves was probably due to the occurrence of high cases of false seronegatives, due to either the calves mounting a strong immune response that might have managed to kill quite a number of cysts as evidenced in Table 2 or poor infectivity of T. saginata eggs administered to them as shown in Table 3. The former explanation describes the concomitant immunity phenomenon, which has long been considered a common feature of worms such as schistosome infections (Coelho et al 1995). Antigens resulting from dead cysticerci are not detected by this assay Onyango-abuje et al 1996) (Table 2).…”