Modulatory role of immunization with secretory-excretory products of schistosoma haematobium eggs on morbidity in infected hamsters

ABSTRACT

A variety of secretory-excretory products [SEPs] from different stages of Schistosoma have been identified to induce a level of host-protective immune responses with amelioration of morbidity. Identification of SEPs complex components can be expected to facilitate discovery of new therapeutic drug targets and new diagnostic markers for schistosomiasis control. The present study was undertaken to evaluate the possible anti-morbidity effects of SEPs of S. haematobium eggs twelve weeks after exposure to infection. The liver and intestinal tissues of infected hamsters were selected for evaluation as in the murine models the urinary bladder exhibits minimal morbidity in response to S. haematobium infection. The experimental design included three groups of 10 hamsters each; SEPs immunized group, infected immunized group and infected control group. Multiple small doses of purified S. haematobium eggs SEPs were injected intra-peritoneally, followed 2 weeks later with 2 booster doses at weekly intervals. Animals were infected with S. haematobium cercariae 1 week following last booster immunization dose. All animals were sacrificed 12 weeks PI. Assessment of the modulatory role of SEPs immunization including worm burden, tissues egg loads, oogram pattern and histopathological examination of liver and intestinal tissues were carried out. Total and subclasses of anti SEPs of S. haematobium eggs IgG, IgM, IgG2 and polyvalent immunoglobulins [Igs] were measured using indirect ELISA at weeks 3, 6 and 9 post-infection [PI]. Immunization with SEPs of S. haematobium eggs produced significant reduction in worm load [61.37%], reduction in tissue egg loads [54.85% and 41.57% for hepatic and intestinal ova, respectively]; decreased percent of immature stages and increase in the percent of dead ova in oogram pattern. Pathological examination also revealed significant reduction in number of hepatic granuloma [46.06%]. At 3, 6 and 9 weeks PI, the level of Igs especially IgG was significantly higher in the infected immunized group, compared to both control groups, reached a peak value at 6 weeks PI [1.6] and remained elevated till the end of the experiment with slightly decreasing tendency at 9 weeks PI [1.3]. This study could represent an immunization model as a trial to decrease severe morbidity of schistosomiasis haematobium which may be aggravated by serious sequels