Association of a functional TNF variant with Plasmodium falciparum parasitaemia in a congolese population.

Several studies have provided evidence of both helpful and harmful effects of TNF on the outcome of Plasmodium falciparum malaria infection. Several TNF polymorphisms that are located within non-coding regions have been associated with parasitaemia, mild malaria or severe malaria. We investigated the association of TNF1304 (rs3093664), TNF-308 (rs1800629), TNF-238 (rs361525) and TNF-244 (rs673) with mild malaria and symptomatic maximum parasitaemia in a population-based design (n=310). We obtained nominal evidence for an association between symptomatic maximum parasitaemia and TNF-308, TNF-238, and TNF-244 on the one hand, and between the number of mild malaria attacks and TNF-244 on the other hand. After accounting for multiple tests, we confirmed the association of symptomatic maximum parasitaemia with TNF-244. We further provide bioinformatics and experimental evidence that TNF-244 has a cis-regulatory effect. This is the first report that emphasizes the potential role of TNF-244 in malaria.

[Malaria in health centres in the southern districts of Brazzaville, Congo]. / Le paludisme dans deux centres de santé au sud de Brazzaville, Congo.

During the surveys on antimalarial drug efficacy carried out from 2003 to 2006, we systematically checked the presence of Plasmodium falciparum in patients consulting in two health centres located in the south of Brazzaville. The first centre is situated in the urban zone; the second, in the semi rural area. The objective of this survey was to determine the prevalence of malaria-infected patients among the consulting patients and the prevalence of symptomatic patients with acute malaria attacks based on the parasitic density. Patients with parasites were assigned to one of the 5 following classifications: <2000, > or =2000, <5000, > or =5000 and > or =10,000 asexual parasites/microl of blood. Based on the threshold of parasite density 10,000 asexual parasites/microl, 10% and 24% of febrile patients in Tenrikyo and Madibou health centres were diagnosed as cases of malaria, respectively; 13.6% and 26.8% of patients under 5 years old consulting in these two health centres had malaria attacks. If the threshold of parasite density is lowered to 2000 asexual parasites/microl for patients > or =15 years old, 8% and 14% of adults in Tenrikyo and Madibou had malaria attacks, respectively The malaria burden was higher in the periphery of the city of Brazzaville than in the urbanized central districts. The Madibou health centre located in semi rural zone receives twice as many malaria cases for consultation than Tenrikyo located in the urban zone.

[Variability of in vitro activity of proguanil and cycloguanil on erythrocyte stages of Plasmodium falciparum as a function of culture conditions]. / Variabilité de l'activité in vitro du proguanil et du cycloguanil sur les stades érythrocytaires de Plasmodium falciparum en fonction des conditions de culture.

The in vitro activity of proguanil, cycloguanil (active metabolite of proguanil), pyrimethamine, and chloroquine was determined for 14 isolates of Plasmodium falciparum and the chloroquine-resistant W2 clone. In vitro assays were performed by using different types of RPMI 1640 culture medium and incubation period. The use of the standard RPMI medium or RPMI medium containing low concentrations of folate and para-aminobenzoic acid increases the 50% inhibitory concentrations of cycloguanil and pyrimethamine, as compared with the use of folate- and para-aminobenzoic acid-free RPMI medium. The concentrations of folate and para-aminobenzoic acid did not affect the in vitro activity of proguanil and chloroquine. However, prolongation of the incubation period from 42 to 66 hours decreased the 50% inhibitory concentrations of all test compounds. The weak antagonism in vitro between chloroquine and proguanil or cycloguanil does not seem to have any repercussion on the in vivo efficacy of chloroquine-proguanil combination.

[No variation in chloroquine resistance (Plasmodium falciparum) from 1986 to 1996 in semi-immune children in Brazzaville (Congo)]. / Niveau de chloroquinorésistance inchangée (Plasmodium falciparum) de 1986 à 1996 chez les enfants semi-immuns à Brazzaville (Congo).

A simplified Plasmodium falciparum in vivo test was carried out in Brazzaville (Congo) in April 1996. Chloroquine was prescribed at 25 mg/kg for 3 days in asymptomatic Brazzavillian school children who presented parasitemia > 800 P. falciparum trophozoïtes and lived in a highly endemic district. A massive decrease of parasitemia was observed on day 2. The percentage of resistance (presence of P. falciparum trophozoïte on day 7 in a thick blood film) was 43.5, 28 and 21 respectively (IC: 95%: 29-57, 15-41 & 10-34) at the threshold of 6, 50 and 100 parasites/microliter. In positive children on day 7 the reduction of parasitemia was > 95% and no case of R3 resistance was detected. A comparison with previous studies carried out in 1985, 1986, 1990 and 1993 in the same school using the same methodology proves the long-lasting stabilization of chloroquino-resistance for this semi-immune indigenous population.

[Comparative efficacy of chloroquine and amodiaquine (25 and 35 mg/kg) in school children infected with P. falciparum (Brazzaville, March 1990)]. / Efficacité comparée de la chloroquine et de l'amodiaquine (25 et 35 mg/kg) chez des écoliers porteurs de P. falciparum (Brazzaville, Mars 1990).

The efficacy of 4 therapeutic schedules was compared in March and April 1990 in Brazzaville school children, aged between 6 and 8 years, with parasitaemia of at least 1,000 trophozoites of Plasmodium falciparum per mm3. It was possible to interpret 125 simplified in vivo tests. The results showed that the activity of amodiaquine is still relatively satisfactory. The activity of chloroquine was slightly lower with the schedule of 25 mg/kg but was good at 35 mg/kg. Although these results were obtained in children who were mostly asymptomatic, they show that the use of amino-4-quinolines is still justified, at least in the initial treatment of uncomplicated malaria in semi-immune congolese subjects.

[Plasmodium falciparum drug resistance in the Congo. Evaluation of surveys carried out from 1985 to 1989]. / La résistance médicamenteuse de Plasmodium falciparum au Congo. Bilan des enquêtes réalisées de 1985 à 1989.

Surveys on drug sensitivity of Plasmodium falciparum carried out between 1985 and 1989 included 7-day in vitro tests and in vivo tests. 485 in vivo tests were carried out in eight surveys conducted in Brazzaville and in several inland regions. The subjects were congolese children aged between 3 months and 15 years old. They were recruited in hospital, mother-child clinics or at school. The drugs studied were chloroquine, amodiaquine and the sulfadoxine-pyrimethamine combination. 182 strains were tested in vitro in two surveys (December 1985 and January 1987); amino-4-quinolines, quinine and mefloquine were studied. Although resistance to amino-4-quinolines is a recent occurrence, by 1985 it had spread widely in the indigenous population in the Centre and South of the country. Resistance has since increased gradually, especially for chloroquine which undergoes specific surveillance. The situation is less serious in the North, a less densely populated region which is still enclosed. In an in vivo comparative study with chloroquine conducted in Brazzaville in November 1986, amodiaquine was found to be only slightly more effective at a similar dosage. At that time, certain isolated observations already seem to imply that the sulfadoxine-pyrimethamine combination was also affected by resistance. This was not corroborated in an in vivo study carried out in 1989 on 40 children presenting with a malarial attack. Although the sensitivity to quinine may probably be decreased. This drug cannot yet be considered as being truly affected by resistance. The activity of mefloquine, the use of which is still limited, was satisfactory in 1987 in two different regions of the country.

[Drug sensitivity of Plasmodium falciparum in vivo and in vitro in Brazzaville (Congo)]. / Chimiosensibilité in vivo et in vitro de Plasmodium falciparum à Brazzaville (Congo).

Various projects were launched in 1993 to monitor the chemosensitivity of Plasmodium falciparum in Congo. Resistance of 34 strains in Brazzaville to chloroquine, quinine and mefloquine and of 35 to halofantrine was investigated in an in vitro survey using an isotopic micro test. The resistance rates were 61.8, 14.7, 3.0 and 0.0% respectively. Thus, the chemoresistance which first appeared in 1990 is confirmed and is stable in the population. This finding was further confirmed by a parallel in vitro analysis of sensitivity to chloroquine in Brazzaville. A chloroquine monitoring network is now being established throughout the country based on simplified WHO tests of 100 asymptomatic schoolchildren conducted every six months. The first results in 1993, from three Southern regions indicate that parasites are found in 20 to 60% of cases seven days after a standard 3 day treatment with 25 mg/kg, according to the region. The results of in vitro and in vivo tests are very variable. Indeed, the value of such results for these tests for national monitoring is questionable: a more reliable system of identifying true therapeutic failures would be better suited.

In vitro drug sensitivity and clinical aspects of Plasmodium falciparum malaria in African children.

In vitro Plasmodium falciparum drug sensitivity was investigated in 115 brazzavillians children, between 1 year and 10 years of age. On the basis of clinical aspects, four groups were constituted: Group 1: 39 asymptomatic school children, Group 2: 16 children with uncomplicated malaria, Group 3: 40 with severe but not pernicious malaria and Group 4: 20 with pernicious malaria. The drugs tested were chloroquine (CQ), quinine (QN) and mefloquine (MQ). The sensitivity level was assessed by a 48-hour in vitro maturation test involving the uptake of tritiated hypoxanthine, the initial blood level of parasite being > or = 0.1% in all cases. For QN and MQ, the median IC50 values showed no significant difference related to clinical status, age or parasitaemia levels. For CQ, the proportion of resistant strains and the 50 inhibitory concentration (IC50) values were greater in the cases of children hospitalised for malaria but there were no differences related to clinical severity of these hospitalised children nor, within each group, to the age or parasitaemia levels. The percentage of subjects with an IC50 value greater than the 90 percentile of the IC50 of the asymptomatic group, which we propose as the severity index related to chemoresistance, was 15% for uncomplicated malaria, 38% for severe but non-pernicious forms and 35% for pernicious malaria. The IC50 for QN was significantly higher in CQ-resistant strains and there was a positive correlation for CQ vs QN and for QN vs MQ.

In vitro activities of DU-1102, a new trioxaquine derivative, against Plasmodium falciparum isolates.

The antimalarial trioxaquine derivative DU-1102, synthesized by covalent linkage between aminoquinoline and trioxane moieties, was highly active against Cameroonian isolates (mean 50% inhibitory concentration of 43 nmol/liter) of Plasmodium falciparum. There was no correlation between the responses to DU-1102 and chloroquine and only a low correlation between the responses to DU-1102 and pyrimethamine, suggesting an independent mode of action of the trioxaquine against the parasites.