In vitro immune recognition of synthetic peptides from the Plasmodium falciparum CS protein by individuals naturally exposed to different sporozoite challenge.

The impact of duration and intensity of sporozoite challenge on the in vitro cell immune response to synthetic peptides of the circumsporozoite (CS) protein of Plasmodium falciparum was investigated in residents of a malaria endemic area in Burkina Faso (West Africa). Lymphocyte proliferation and interferon-gamma (IFN-gamma) production were used to assess immune recognition of synthetic peptides corresponding to the polymorphic Th2R and Th3R regions, to the conserved CS.T3 sequence and to NANP and degenerate NVDP repeats. Immune responses were measured in adults and children from a village where they received more than 100 sporozoite inoculations per year and in adults living in a town, exposed to a 10-100 times lower challenge. A lifetime intense exposure apparently increased the ability to proliferate in response to most peptides in the rural adults, who all produced antibodies to NANP repeats. Surprisingly, cell cultures from these subjects seldom contained appreciable levels of IFN-gamma. In the urban adults, possibly due to the moderate challenge they are exposed to, significant differences in the proliferative potentials of the peptides could be detected. The highest stimulation indices were obtained with the genetically unrestricted CS.T3 peptide. Remarkably, proliferative responses to Th2R and Th3R appeared to be correlated with the humoral response to the CS protein, indicating a T helper significance of the epitopes. The differing proliferative potential of the polymorphic epitopes in the urban adults suggests that polymorphism might delay the development of immune responsiveness under conditions of sporadic transmission. The children from the highly malarious village displayed the lowest proliferative scores, accompanied by a high prevalence of antibodies to NANP repeats. On the basis of these findings, the hypothesis is proposed that a pure B cell reactivity to NANP repeats could ontogenetically precede the mounting of a conventional T-B cooperative immune response.

Ten-year surveillance of drug-resistant malaria in Burkina Faso (1982-1991).

To understand the evolution of drug-resistant forms of malaria in time and in space, we carried out an analysis of the results of a series of passive and active surveys conducted in Burkina Faso between 1982 and 1991. A total of 607 tests for resistance to chloroquine and mefloquine were carried out in vitro and 3,679 tests for resistance to chloroquine, quinine, and sulfadoxine-pyrimethamine were performed in vivo. The surveys principally involved the two main cities of Burkina Faso, Ouagadougou and Bobo-Dioulasso. However, another 10 locations representing the three different zones of malaria transmission were also studied. The first cases of Plasmodium falciparum resistant to chloroquine in vitro were reported in 1983, but it was only in 1988 that in vivo resistance appeared. The first cases of in vitro resistance to mefloquine were noted in 1987 while chloroquine sensitivity at a high rate (15.8%), which decreased during the following years. The prevalence of resistance to chloroquine increased in parallel to this decrease in sensitivity to an overall peak of 41% in vitro and 16% in vivo in 1990. These rates then decreased to 3% and 6%, respectively, in 1991. This pattern of decreasing resistance was broadly similar in all sites except for the town of Bobo-Dioulasso, where the level of resistance remained stable at approximately 14% from 1988 to 1991. Only two cases of resistance in vivo to sulfadoxine-pyrimethamine were noted.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo sensitivity of Plasmodium falciparum to halofantrine hydrochloride in Burkina Faso.

Plasmodium falciparum susceptibility to halofantrine hydrochloride was investigated in a small village near Ouagadougou, Burkina Faso, where the parasite was known to be chloroquine resistant. An in vivo test was carried out in July 1992 at the beginning of the rainy season in children ranging in age from two to eight years with P. falciparum monospecific infections, asexual parasitemia greater than 800/microliters of blood, and a negative result on a Bergqvist urine test for 4-aminoquinolines. Among 206 children screened, 74 were selected for study. Blood samples were collected on days 0, 2, 4, 7 and 14, and 100 microscopic fields of thick and thin blood smears were examined for parasite density and species identification. Halofantrine hydrochloride was administered under supervision at the standard dose of 24 mg/kg as 8 mg/kg given three times at 6-hr intervals with an observation period of 1 hr after each 8-mg/kg dose. Parasitemias cleared in all 74 cases by day 7, but there was a recurrence of parasitemia in six subjects (8.1%) on day 14. A second course of therapy with halofantrine resulted in prompt clearance of parasitemias in all of these children. The drug was well-tolerated and the hematologic and biochemical indices were not adversely affected by treatment.

Detection and anatomical localization of Plasmodium falciparum circumsporozoite protein and sporozoites in the afrotropical malaria vector Anopheles gambiae s.l.

Salivary glands from Anopheles gambiae s.l. collected in Burkina Faso, West Africa, were analyzed by both microscopic examination and immunoradiometric assay to determine the Plasmodium falciparum sporozoite rates. Using the same mosquito samples, the immunoassay revealed positive salivary glands with low sporozoite loads, which were frequently missed by microscopy. A closer agreement between both techniques was found using salivary glands with high sporozoite loads. We also found a number of mosquitoes with uninfected salivary glands which harbored the circumsporozoite antigen in their thoraces. In a particular village these mosquitoes represented 43.5% of all sporozoite antigen carrying specimens.

Permethrin-impregnated curtains in malaria control.

The impact of permethrin-impregnated curtains on the incidence of malaria episodes, parasitaemia and splenomegaly was assessed during a 22 month period in 2 groups of children aged 0.5-6 years. One group lived in houses where permethrin-impregnated curtains had been installed, the other group lived in houses without curtains. A significant reduction of incidence of malaria episodes, mean parasite density, parasite prevalence and splenomegaly was consistently observed in the intervention group towards the end of the period of moderate transmission, whereas no clear-cut impact could be demonstrated during the high transmission period. The influence of malaria pressure and community utilization on the protective efficiency of curtains is discussed. Because of their acceptability and the ease of reimpregnation, curtains proved to be a suitable technique for integration into primary health care.

Prevalence and levels of antibodies to the circumsporozoite protein of Plasmodium falciparum in an endemic area and their relationship to resistance against malaria infection.

A study on malaria transmission, prevalence of infection and anti-sporozoite antibodies was carried out in Burkina Faso (West Africa). The prevalence and the levels of antibodies to (NANP)3 were found to be related to the entomological sporozoite inoculation rates measured at the same time in a defined area. The major inducer of anti-(NANP)3 antibody production under field conditions is sporozoite inoculation by infected mosquitoes. Levels of antibodies to (NANP)3 vary considerably with age and transmission season. High levels of anti-(NANP)3 antibodies raised under field conditions might offer protection against small inocula of sporozoites.

Further observations on chemoprophylaxis and prevalence of malaria using questionnaire data in urban and rural areas of Burkina Faso.

A cross-sectional study of malaria prevalence (98.6% Plasmodium falciparum) was carried out in Ouagadougou (Burkina Faso) and in 3 neighbouring villages on 2117 children, zero to five years old. Data on antimalarial prophylaxis and treatment were obtained from the child's parent using an interviewer-administered questionnaire. Regular weekly chloroquine consumption lowered the parasite rate but a significant increase with respect to parasite density was recorded in protected children from the rural area. No significant differences related to previous antimalarial treatments were observed in parasite rate or density. Antimalarial treatments were less frequent in children under chemoprophylaxis. Information about dosage and date of therapy was not recalled by most of the interviewed parents. Problems and suggestions for questionnaire data are briefly discussed.

[Prevalence of malaria in Ouagadougou and the surrounding rural environment during the period of maximal transmission]. / Prévalence du paludisme à Ouagadougou et dans le milieu rural limitrophe en période de transmission maximale.

The prevalence of malaria infections was estimated in six different areas of the town of Ouagadougou, Burkina Faso, and in three neighbouring villages. Thick and thin blood films from a total of 2,117 children less than 5 years old were examined at the peak of the transmission season (August-September). Plasmodium falciparum was found in more than 98% of the positive slides. The overall parasite index at Ouagadougou was 16%, while indices from 51 to 88% were recorded in the three villages. Significant differences were observed between the six urban areas within the town as well as between the three villages. The highest parasite rates in the town were clearly associated with major breeding places of An. gambiae s.l. indicating a remarkable focality of transmission. Significant differences were observed between groups of children from houses only 300 m apart. Chemoprophylaxis appears to play an important role in determining parasite rates lower than expected in one of the three villages.

[In vivo chemosensitivity of Plasmodium falciparum to chloroquine in Burkina Faso: development of resistance 1988-1990]. / Surveillance de la chimiosensibilite in vivo de Plasmodium falciparum a la chloroquine au Burkina Faso: evolution de la resistance 1988-1990.

A study of Plasmodium falciparum sensitivity to chloroquine was carried out in 1988 and 1990 in 5 localities, representatives of different climatic areas of Burkina Faso. The 7-day in vivo standard test performed in 1988 showed a total clearance failure of 25%. No significant difference with 1990 data was found, except for an increase of the resistance in the area of Fada N'Gourma, close to the border with Benin, Niger and Togo.

Sensitivity to antimalarial drugs by Plasmodium falciparum in Goundry, Oubritenga province, Burkina Faso.

Plasmodium falciparum susceptibility to chloroquine in vivo and to chloroquine, mefloquine, quinine, amodiaquine and sulfadoxine/pyrimethamine in vitro was investigated in children living in Goundry village, Oubritenga Province (Burkina Faso) in November 1992. An extended WHO in vivo field test was used, with follow-up on days 2, 4, 7, 14, 21 and 28 after treatment with 25 mg chloroquine per kg body weight given over 3 days, in children from 2 to 8 years old with P. falciparum monospecific infection, asexual parasitaemia > 800 parasites/microliter of blood and negative Bergqvist urine tests. At the same time, the in vitro response was assessed using WHO standard test kits. Out of the 71 in vivo responses examined, 50 (70.4%) were classified as resistant to chloroquine at RI (43.6%) or RII (26.8%) levels. There were no RIII responses. Out of the 43 isolates tested for chloroquine susceptibility in vitro, 32 (74.4%) were resistant to the drug with mean EC50 and EC99 values of 1.41 mumol and 10.96 mumol/l of blood, respectively. Resistance to sulfadoxine/pyrimethamine in vitro was observed in one out of 19 tested cases, with mean EC50 and EC99 values of 0.00002 mumol and 35.05 mumol/l of blood, respectively. All isolates were inhibited by mefloquine at 12.8 mumol/l of blood, quinine at 51.2 mumol/l of blood and amodiaquine at 0.4 mumol/l of blood, indicating full sensitivity to these 3 drugs. The present study demonstrates the high prevalence of chloroquine-resistant strains of P. falciparum in the study area of Burkina Faso and indicates that isolates resistant to sulfadoxine/pyrimethamine may also be present.

Susceptibility of Plasmodium falciparum to chloroquine and mefloquine in Ouagadougou area (Burkina Faso).

Plasmodium falciparum susceptibility to chloroquine in vivo and to chloroquine and mefloquine in vitro was investigated in children living in Ouagadougou area (Burkina Faso) in October 1991. The 7-day WHO in vivo field test was used, with follow-up on days 2, 4, 7 after treatment with 25 mg base of chloroquine per kg body weight given over 3 days, on children aged 2-8 years with monospecific P. falciparum infection (parasite density higher than 800 asexual parasites/microliters of blood), and negative Bergqvist urine tests. At the same time, the in vitro response was assessed using WHO standard test kits. Chloroquine treatment in vivo resulted in parasite clearance in 47 subjects (92.2%) within 7 days (S/RI responses). Parasitaemia did not clear in 4 cases (7.8% of RII responses). There were no RIII responses. The sensitivity study in vitro showed a low degree of chloroquine resistance in 2 out of 12 isolates tested and a mean 50% effective dose (EC50) and EC99 of 0.12 mumol and 1.47 mumol/litre of blood, respectively. All isolates tested were inhibited by mefloquine at 1.6 mumol/litre of blood, indicating full sensitivity. The present study demonstrates that first-line treatment with chloroquine is still satisfactorily effective in the study area of Burkina Faso.

Waiting for the vaccine: sporozoite vaccine research entails important progress in malaria epidemiology.

The research efforts aimed at developing a vaccine against malaria, although failing thus far in their main objective, have produced molecular tools of great utility for epidemiological studies. For example, monoclonal antibodies directed against the repeats of Plasmodium circumsporozoite (CS) protein allowed the 2-site assay for detecting sporozoites in mosquitoes to be established. This immunoassay is advantageous compared with the conventional method of salivary gland dissection and microscopic examination, for it makes the identification of the sporozoite species possible, thanks to species-specific aminoacid sequences of the CS repeats. Other examples of vaccine research-derived tools are synthetic peptides reproducing the repetitive part of the CS protein, which allow antibodies to sporozoites, in individuals exposed to malaria, to be detected. Antibodies to the CS repeats of Plasmodium (Laverania) falciparum proved to be a reliable indicator of the intensity of malaria transmission and, therefore, were suitable for monitoring the impact of malaria control programmes. Finally, a project is outlined that, relying on the application of these tools, will aim at characterizing the transmission of Plasmodium (Plasmodium) malariae and at unveiling the possible relationship among different species thriving in the same distribution area, an issue which may become of relevance in view of the likely introduction of a vaccine directed against a single species.

[Utilization of permethrin-impregnated curtains by the inhabitants of a rural community in Burkina Faso]. / Utilisation de rideaux impregnés de perméthrine par les habitants d'une communauté rurale du Burkina Faso.

The degree of utilisation of permethrin-impregnated curtains was assessed in a rural community near Ouagadougou, Burkina Faso. Results showed that in the first half of the night, until 11-11.30 p.m., curtains were only partially used by the community. Indeed by this time around 50% of houses had doors well protected by curtains and, over 35% of the community, children and adults, were staying outside. A very marked pattern of this behavior was found, wrong utilisation of curtains being higher in the warm season and lower in the cold season. On the one hand, this situation decreased the potential action of curtains as a barrier to avoid mosquito-man contact and, on the other hand, facilitated the exposure of community to the risk of outdoor infection. These findings may explain the variable level of efficacy showed by curtains in the prevention of malaria morbidity, which seems to be higher in the period between January and February, the winter season in Burkina Faso. The possible application of impregnated curtains as a community-based vector control method is discussed.

Immunity to Plasmodium sporozoites: recent advances and applications to field research.

The presence of antibodies against Plasmodium falciparum sporozoites in humans living in malaria endemic areas was measured using as antigen the synthetic peptide (NANP)3, which represents the immunodominant region of the circumsporozoite (CS) protein. The results indicate that: i) the production of anti-CS antibodies is unrelated to the presence in the circulation of blood-stage parasites; ii) anti-CS antibodies, raised by natural inoculation, could exert a protective role against natural malaria infection; iii) anti-CS antibodies can be used as indicators of the intensity of malaria transmission.

CS antigen localization in malaria vectors: hypothetical refractoriness to transmission observed in the field.

Indoor resting Anopheles gambiae s.l. were collected in two villages near Ouagadougou, Burkina Faso, and processed to investigate the presence and distribution of Plasmodium sporozoites. Salivary glands were dissected, examined by phase contrast microscopy and further processed by IRMA in order to reveal the presence of the circumsporozoite (CS) antigen of P. falciparum. The corresponding thoraces were homogenized and processed by IRMA. In the village characterized by the higher inoculation rate more than 40% of the infected mosquitoes were not found infective since CS antigen was detected in the thorax in absence of sporozoites and CS antigen in the corresponding salivary glands.

Plasmodium falciparum malaria in sympatric ethnic groups of Burkina Faso, west Africa.

Plasmodium falciparum parasite rate, parasite density and anti-CS antibodies were assessed in 196 subjects (age > 10 yrs) belonging to three sympatric West African ethnic groups, namely Mossi, Rimaibé and Fulani, all exposed to very high seasonal malaria transmission in the same rural village near Ouagadougou, Burkina Faso. No interethnic differences were noted in the use of antimalaria measures nor in the exposure to malaria vectors. However, interethnic differences were found in each of the three malariological indices. The Fulani appeared markedly less parasitized and more responsive to the CS-antigen than the Mossi and the Rimaibé who had very similar indices, except in the case of parasite density. These findings suggest a higher resistance to malaria of the Fulani ethnic group, possibly involving human genetic factors and/or the influence of extrinsic variables (e.g., socio-cultural) among which diet differences should be considered.

[Impact of utilization of permethrin impregnated curtains on malaria in a rural zone of high transmission in Burkina Faso]. / Impact de l'utilisation des rideaux imprégnés de perméthrine sur le paludisme dans une zone rurale de haute transmission au Burkina Faso.

The efficacy of permethrin impregnated curtains as a malaria control measure was evaluated in a rice field area nearby Ouagadougou (BF). Two groups of children aged 1-5 years matched for age, sex and malaria exposure, were followed through the rainy season of 1987 for illness and febrile episodes. One group of 118 children lived in houses protected with impregnated curtains, the other in houses without curtains. All children were examined for parasitaemia spleen index packed cell volume (PCV) and antisporozoites antibodies at the beginning and the end of the rainy season. During rainy season no difference could be found in the number of clinical episode between the two groups. A reduction in the prevalence of splenomegaly and parasitaemia and an increase in the PCV was observed during the dry season.

[Clinical signs of severe malaria in a pediatric hospital in Ouagadougou]. / Formes cliniques du paludisme grave en milieu hospitalier pédiatrique à Ouagadougou.

During the period of transmission of malaria, from August to November of 1993 and 1994, we conducted a study to determine the frequency of the clinical forms of severe and complicated malaria. The study involved children, from 6 months through 15 years old, admitted to the pediatric ward of the hospital in Ouagadougou, Burkina Faso. The criteria for inclusion followed the definition of severe malaria stated by the World Health Organization. We carefully noted the symptoms and signs on admission. Of the total of 719 children enrolled in the study, there was a prevalence of children under 5 years old. The most frequent clinical forms were those of coma (377 cases, 52.4%), prostration (268 cases, 37.3%), convulsion (152 cases, 21.4%), anemia (115 cases, 15.9%), and hypoglycemia (55 cases, 10.3%). No renal failure form was observed. We also observed the respiratory distress form (35 cases, 4.9%) and the hemorrhagic form (11 cases, 1.5%). Malaria remains a major cause of childhood morbidity and mortality in the developing world. Early therapeutic management of febrile attacks with chloroquine would reduce the incidence of severe and complicated malaria.

A national survey of the prevalence of chloroquine resistant Plasmodium falciparum in Burkina Faso.

Plasmodium falciparum susceptibility to chloroquine was investigated in 10 areas of Burkina Faso in the rainy seasons in 1990-1991. The 7-days in-vivo test was carried out from August to November on children aged 2-8 years with monospecific P. falciparum infection (asexual parasitaemia > 800 microliters-1 of blood), axillary temperature < 37.5 degrees C, and a negative Bergqvist urine test for 4-aminoquinolines. Among 2190 children screened, 366 were selected. Blood samples were collected on days 0, 2, 4 and 7 by finger-prick, and 100 microscopic fields of thick and thin smears were examined for parasite density and species identification. Chloroquine was given under supervision at the standard dose of 25 mg kg-1 over three days (days 0, 1 and 2) with an observation period of one hour after treatment. Parasitaemia did not clear in 63 cases (17.2%) with a 13.4% RII response and 3.8% RIII response. The results do not seem to indicate a decline in the sensitivity of P. falciparum to chloroquine in Burkina Faso during the past two years.