Showing papers by "Marcel Tanner published in 1996"

Plasmodium falciparum malaria in the first year of life in an area of intense and perennial transmission

Abstract: A longitudinal study of Plasmodium falciparum malaria in infants in Idete village, south-eastern Tanzania, was conducted over a period of 14 months in order to determine the incidence of P. falciparum infection and clinical malaria in the first year of life. Of 1356 blood slides from cross-sectional surveys, 52.1% were positive for asexual stages of P. falciparum. There were marked increases in P. falciparum prevalence, parasite densities, overall fever incidence and the incidence of malaria fevers with age for the first 6 months of life. The average attack rate, estimated from a reversible catalytic model, was 0.029 per day with a slight increase with age but there was no initial period of protection against infection in neonates. Estimated average duration of infections was 64 days, with infections in older infants lasting much longer than those contracted during the first 2 months of life. These results support the hypotheses that the main effect of passively transferred maternal immunity to malaria is in the control of asexual stage parasites, and that the level of clinical immunity depends upon the extent of recent exposure to parasites. Infants as young as 4 months of age are at high risk of clinical attacks. Intervention programmes against malaria in areas of the highest transmission should therefore be designed to include this group.

Cytotoxic T lymphocytes to Plasmodium falciparum epitopes in an area of intense and perennial transmission in Tanzania.

Abstract: Studies in The Gambia have provided indirect evidence that cytotoxic T lymphocytes (CTL) play a protective role against malaria in humans and recently, using allele-specific HLA class I peptide motifs, several peptide epitopes for CTL in four pre-erythrocytic Plasmodium falciparum antigens have been identified in naturally exposed Gambians. However, CTL levels were low, suggesting that boosting these low levels by immunization might provide substantial protection. In the Kilombero valley of Tanzania, malaria transmission is holoendemic and 300 times more intense than in The Gambia. We report here that several of the epitopes identified in The Gambia are also recognized in naturally exposed, partially immune Tanzanian adults and that levels of CTL are similar to or slightly higher than in Gambian subjects, despite the much higher inoculation rate. We report a new HLA-A2.1-restricted epitope from the thrombospondin-related anonymous protein (TRAP) and we demonstrate that peptide epitopes in TRAP are naturally processed for recognition by CTL from naturally exposed humans. The common allele of a variable HLA-B7-restricted epitope in the circumsporozoite protein behaved as an altered peptide ligand (APL) with respect to CTL cognate for a rarer allelic variant of this epitope, suggesting that APL antagonism may occur in natural CTL responses to P. falciparum. The moderate levels of CTL observed, even in this area of intense malaria transmission, points to the need to assess candidate vaccines aimed at increasing CTL levels.

Duration of protection and age-dependence of the effects of the SPf66 malaria vaccine in African children exposed to intense transmission of Plasmodium falciparum.

Abstract: The SPf66 synthetic vaccine is safe and partly efficacious against Plasmodium falciparum malaria among children 1-5 years old. The estimated vaccine efficacy [VE] for all clinical episodes over a period of 18 months after the third dose is 25% (95% confidence interval [CI], 1%-44%; P = .044). The observed temporal variations in efficacy could have been due to chance (likelihood ratio chi 2 = 13.8, 8 df; P = .086). Efficacy against clinical malaria did not vary significantly with age (chi 2 = 1.07, 4 df; P = .90). Overall parasite density was 21% lower in vaccine recipients than in the placebo group (95% CI, 0%-38%; P = .044). Further development of SPf66 may require trials to evaluate safety, immunogenicity, and efficacy when administered in the first year of life, together with other vaccines contained in the Expanded Programme of Immunization schedule.

Malaria and Casual Sex: What Travelers Know and How They Behave.

Abstract: Background: Travelers to the tropics have been reported to comply poorly with recommendations regarding malaria and AIDS. This study addresses the problem of influencing travelers' behavior through different approaches to conveying advice. Method: 3509 people attending a large travel clinic were randomly allocated to different interventions, including brochures about the implications of "sex tourism" and the possibility of participating in a contest assessing knowledge of malaria and AIDS. A comparison group (n = 607) of travelers to Kenya was contacted at an airport. Anonymous, self-administered questionnaires were sent to all travelers after their return. Results: Compliance with chemosuppressive regimen for malaria was 87%. Well-informed travelers did not protect themselves more efficiently against malaria. The efficacy of a given intervention was found to vary according to the age, sex, or travel experience of the participants. Of travelers, 51% reported casual sex abroad (M/F: 69/31). Thirty-eight percent of these contacts were unprotected. Casual sex abroad and condom use were correlated with a history of casual sex in the home country. Condom use was especially low in young women, who were also more likely to have casual sex with fellow travelers than with local partners. Eight percent of the "sex tourism" brochure readers had engaged in casual sex with local partners (all travelers, 4%). Conclusions: Lack of knowledge does not appear to be the problem. Travelers need to be motivated to put their knowledge into practice. Our results suggest that risks relating to malaria and AIDS are perceived in a different manner and that counseling should be individualized. Contest questions can help start a discussion on ethical and health-responsible behavior. The target group of the "sex tourism" brochure was reached, but their behavior appears not to have changed. Objective criteria can help physicians recognize "high-risk" travelers. Travelers need to be made aware that they may encounter environments conducive to risky behavior and that, while abroad, they may react in unexpected ways.

Different approaches to modeling the cost-effectiveness of schistosomiasis control.

Abstract: The limited economic resources available for health care in developing countries necessitates the involvement of cost analysis in the planning of any control intervention. A number of studies have undertaken cost-effectiveness analysis of schistosomiasis control, and the methodologies utilized in both cost and effectiveness evaluation are discussed. In attempting to relate cost to effectiveness, most studies have utilized static models expressing effectiveness in terms of coverage (drug delivery) or cure rate (infection prevalence reduction). These immediate output measures do not consider the long-term impact of control nor the effect on disease. An alternative approach is to use a model of the transmission dynamics of the parasite to permit evaluation of the long-term impact of control. An example of a population dynamic approach to cost-effectiveness analysis that can assess the impact of treatment on infection and disease due to the intestinal nematodes is presented to illustrate the potential of this approach in modeling the cost-effectiveness of schistosomiasis control.

Helminth infections, morbidity indicators and schistosomiasis treatment history in three villages, Dongting Lake region, PR China

Abstract: In order to estimate the public health impact of helminth infections, and to provide baseline data for interventions, parasitological and morbidity surveys were conducted among inhabitants of three villages in Dongting Lake region, Hunan Province, China. Ascaris lumbricoides was found to be the most common helminth infection, followed by Trichuris trichiura and Schistosoma japonicum. Left liver enlargement was the most common indicator of morbidity. Observed numbers of multiple species infections closely correlated with expected figures generated from a simple probabilistic model. Heterogeneity was observed in age and sex-standardized infection and morbidity prevalences among the villages and occupations. Males had higher levels of infection, were more likely to suffer morbidity, and were more likely to have been treated for schistosomiasis than women. The prevalence of each morbidity indicator was positively correlated with the number of times of treatment for schistosomiasis, and negatively correlated with number of years since last treatment. The results imply that treatment history for S. japonicum infection may be a good indicator of current morbidity risk.