Schistosoma haematobiumin the baboon (Papio anubis): assessment of protection levels against either a single mass challenge or repeated trickle challenges after vaccination with irradiated schistosomula

Abstract

Baboons vaccinated intramuscularly with three times 9000 20 krad irradiated Schistosoma haematobium schistosomula at monthly intervals were exposed percutaneously to either a single mass challenge of 3000 (VMC) or ten, weekly trickle challenges of 300 (VTC) normal S. haematobium cercariae. Unvaccinated mass (MCC) or trickle (TCC) challenge controls were exposed simultaneously. Faecal and urine egg production was delayed in the vaccinated groups which also had reduced adult, particularly female, worm recoveries. Total faecal, urine and tissue eggs were lower in the vaccinated groups, as also were the size of granulomata and the gross pathology and severity of inflammatory responses in the bladder and ureters, except for an increased proportion of tissue eggs in the livers of vaccinated animals. Differences in pathology between groups were less marked in the other organs. Most indices were reduced in the trickle versus the mass challenge control groups. Some of these trends were statistically significant, mostly in the trickle vaccination group (VTC), but others were not. Compared with the appropriate unvaccinated controls, the percentage reduction for the trickle challenge (VTC) group (73%) was three times greater than that of the mass challenge (VMC) group (23%). Overall, the protective effect of vaccination was more clearly demonstrated in the trickle than in the mass challenge groups. This conclusion is based on a single experiment. Nevertheless, because trickle infections probably approximate more closely to what humans receive naturally, it is recommended that they should be used for future testing of all potential vaccines in baboons.

Cross-species protection: Schistosoma mansoni Sm-p80 vaccine confers protection against Schistosoma haematobium in hamsters and baboons

“…On the other hand, baboons exhibited a wide spectrum of urogenital-associated pathological manifestations associated with S. haematobium and thus important pilot data on worm burden, egg retention in tissues and expulsion in feces/urine, for Sm-p80 vaccine, were obtained. This reiterates previous studies in which S. haematobium irradiated cercarial preparations were used in baboons and provided excellent efficacy [35–37]. In our study here in the baboon model significant reductions in worm burden, trapped eggs in the urinary bladder, and egg expulsion in urine/feces were observed following vaccination with the Sm-p80 based vaccine.…”

Experimental vaccines in animal models for schistosomiasis

“…Furthermore, baboons develop a human-like acute schistosomiasis syndrome after exposure to the cercariae of S. mansoni, manifested by fever, eosinophilia, leucocytosis, cachexia, anorexia, and diarrhea, and these symptoms are coincident with the start of egg deposition in the tissues by newly matured worms (Damian et al 1992;Farah et al 2001;Kariuki and Farah, 2005;Alan et al 2006). Furthermore, baboon as a "protection" model has been utilized successfully by several laboratories to test the efficacy of different schistosome vaccines (Sturrock et al 1985;Boulanger et al 1991b;Soisson et al 1993;Reid et al 1995;Yole et al 1996;Kanamura et al 2002;Kariuki et al 2004;Kariuki and Farah, 2005;Siddiqui et al 2005b;Kariuki et al 2006). For example, immunization of baboons with Sm28GST in the presence of alum resulted in protection from a reduction from 0% to 80% (mean=38%) in the number of parasites and a 33% decrease in female fecundity (Boulanger et al 1991b).…”

Resistance to re‐infection after exposure to normal and attenuated schistosome parasites in the baboon model

“…The degree of protective immunity in many of these studies correlated with an increase in serum levels of parasite-specific IgG antibody, implying that baboon schistosome-specific antibodies participate in the development of protective immunity. Vaccination also led to decreased pathology, manifested as smaller granulomas (32,(35)(36)(37). In addition, generalized pathology that affects the liver and colon, including villous atrophy, hypertrophy of the muscularis mucosa and goblet cell hyperplasia, were less marked in vaccinated, compared to control baboons (37).…”