Immunity after treatment of human schistosomiasis mansoni. I. Study design, pretreatment observations and the results of treatment

Abstract

This paper describes the design of a study on immunity to reinfection after treatment of children with Schistosoma mansoni infections, the initial observations on transmission that led to the selection of the study population, the effects of treatment, and the results of immunological tests carried out before and at five weeks after treatment. Iietune village in Machakos District, Kenya, was selected on the basis of high prevalence and intensities of infection in a small preliminary survey, a stable population living in a small area amenable to detailed study, and a lack of previous intervention in the area. Subsequent observations over a pretreatment period of one year confirmed that prevalence and intensities of infection among children attending the local primary school were high. This was associated with extensive contact of members of the community with water-bodies shown to contain large numbers of infected snails. Analysis of pretreatment intensities of infection and water contact patterns in the schoolchildren allowed the selection of 129 children showing a broad scatter between: (a) high intensity, low water contact, and predicted to be non-immune, and (b) low intensity, high water contact, and predicted to be immune. These children were treated with oxamniquine, 30 mg/kg in divided doses. Five weeks after treatment, 70% of children showed apparent complete cure, and the over-all reduction in geometric mean egg output was 98.9%. Since these children represented only a small proportion of the whole community, there was no obvious reduction in transmission, as reflected by snail infection rates, during the following five-month period. Thus, we are in a position to determine whether successfully treated children do or do not become reinfected in a high transmission environment in which it will be possible to make direct estimates of exposure. Immunological tests carried out immediately before treatment were consistent with a pattern of high exposure leading to the early expression of immune responses in most infected children. Eosinophil levels were elevated in 61% of the children, all of whom showed detectable levels of antibodies against adult worm and egg antigens, as measured by ELISA. In addition, all patients showed antibodies capable of mediating eosinophil-dependent killing of schistosomula. At five weeks after treatment, eosinophil counts and anti-adult worm antibody levels had risen, whereas anti-egg antibodies remained grossly unchanged. The wide variation in the levels of responses shown by different individuals will allow us to test whether such responses are associated with resistance to reinfection during the follow-up period.

T-Helper-2 Cytokine Responses to Sj97 Predict Resistance to Reinfection withSchistosoma japonicum

“…Despite our attempt to quantify this exposure, we were unable to detect a continuous linear relationship between observed water contact and reinfection intensity; however, we did detect lower reinfection in individuals with very low (lower 2.5 percentile) versus higher observed water contact. As expected, we detected an inverse relationship between age and reinfection (10) as well as decreased reinfection in females compared to males (2,9).…”

Previous or Ongoing Schistosome Infections Do Not Compromise the Efficacy of the Attenuated Cercaria Vaccine

“…In both experiments drug treatment failed to boost antibody levels, which is surprising given the amount of antigen that would be released into the bloodstream following worm death. This was not the experience with responses in human populations, where there was a significant rise in antibody levels 5 weeks after drug treatment of schoolchildren (2,19). It seems unlikely that the discrepancy can be attributed to differences in worm burden between the cited human study and our own because fecal egg output was comparable.…”

The impact of repeated treatment with praziquantel of schistosomiasis in children under six years of age living in an endemic area for Schistosoma haematobium infection

“…Information on schistosomiasis infection from a number of different geographical settings indicates that infection intensities and the development of immunological resistance to infection are related, in some way, to age (Butterworth et al 1984, 1985, 1992, Dessein et al 1992, Roberts et al 1993. Infection levels are normally highest in children and following chemotherapeutic cure, children are more rapidly reinfected and at higher rates than older children and adults , Butterworth et al 1992).…”