Malaria transmission and the sensitivity of aggressive mosquitoes to insecticides in a poorly urbanized area of the Deido health district in Douala (Cameroon).

The design of an appropriate strategy for mosquito control in urban areas must take into account the local ecoclimate and its particularities. This study sought to determine the dynamics of malaria transmission and the level of insecticide susceptibility of aggressive mosquitoes in Ndogbong, a poorly urbanized district of Douala. Mosquitoes were captured on volunteers in 4 houses and outdoors for 2 consecutive nights a month, from April to September 2014, and identified by molecular and morphologic techniques. The infectivity of vectors was determined by a circumsporozoite protein (CSP) ELISA test. The susceptibility of vectors to DDT, deltamethrin, and permethrin was also assessed. Overall, 3794 mosquitoes belonging to 6 species were captured in 96 person-nights. The aggressive mosquito fauna comprised : Culex pipiens (57.83%), Cx. poicilipes (1.45%), Anopheles gambiae s.l. (39.01%), Aedes albopictus (1.51%), and An. paludis (0.10%). An. coluzzii accounted for 97% of members of the Gambiae complex captured and was the only species found to be infected with P. falciparum, with an average infection rate of 1.9% (95% CI : 0.82-4.41). The mean entomological inoculation rate was estimated at 0.3 ib/p/n. Susceptibility testing on female An. gambiae s.l. and Cx. pipiens revealed mortality rates lower than 85 % and thus suggested strong resistance to insecticides. An. Coluzzii develops well in poorly urbanized built-up areas of Africa and appears to be the major malaria vector in Ndogbong, especially during the rainy season. The high resistance to insecticides observed requires the development of new formulations for insecticides.

[Anopheles gambiae, major malaria vector in Logbessou, a peri-urban area of Douala (Cameroon)]. / Anopheles gambiae, vecteur majeur du paludisme à Logbessou, zone péri-urbaine de Douala (Cameroun).

An entomological survey was carried out from August to November 2013, in order to determine the vector system of a building site for social housing in a coastal periurban district of Douala (Cameroon). Mosquito larvae were collected and adult endophilic mosquitoes captured on volunteers, for a total sample of 4897 mosquitoes. Morpho-taxonomic techniques alongside molecular techniques enabled the identification of 4 species, all aggressive to humans: Cx. pipiens (22.3%), Ae. albopictus (0.3%), An. coluzzii and An. gambiae (77.4%). The overall average biting rate recorded was 41.73 bites/person/night (b/p/n). An. gambiae s.l. represents 90.82% of this aggressive fauna, followed by Cx. pipiens (8.58%) and Ae. albopictus (0.6%). The detection of CSP showed that An. gambiae was responsible for 100% of P. falciparum transmission. The overall mean Entomological Inoculation Rate (EIR) was 3.94 ib/p/n. Female An. gambiae mortality rates were 14.47%, 82.5% and 100% respectively with DDT, permethrin and deltamethrin. The proliferation of An. gambiae in this area during raining season, at the detriment of An. coluzzii Coetze & Wilkerson and An. melas Theobald known to be major malaria vectors in island and coastal areas of Africa, may owe to the forest that still colonises this coastal peri-urban locality. Residents should therefore make use of deltamethrin based protective measures.

Malaria chemotherapy trial at a minimal effective dose of mefloquine/sulfadoxine/pyrimethamine compared with equivalent doses of sulfadoxine/pyrimethamine or mefloquine alone.

In murine malaria the addition of mefloquine to sulfadoxine/pyrimethamine has been shown to exert an additive effect and to significantly slow the emergence of resistance to the individual components. In a pilot study carried out in Gabon, a reduced dosage of the triple combination with a mean of 1 mg/kg of mefloquine/2 mg/kg of sulfadoxine/0.1 mg/kg of pyrimethamine (Fansimef; Roche, Basel, Switzerland) had previously been shown to achieve high cure rates in Plasmodium falciparum malaria. To evaluate the additive effect, a randomized, double-blind trial in school children with mild P. falciparum malaria was performed in Gabon. Two hundred thirty-one patients evaluated received a single dose of either the triple combination with a mean of 1.07 mg/kg of mefloquine/2.14 mg/kg of sulfadoxine/0.11 mg/kg of pyrimethamine (group MSP), or 1.07 mg/kg of mefloquine alone (group M), or 2.14 mg/kg of sulfadoxine/0.11 mg/kg of pyrimethamine alone (group SP). In the MSP group and the SP group, 67% and 69% of the patients were parasitologically cured, respectively, compared with only 13% in the M group (P < 0.001). A significantly higher parasitemia was found in the M group compared with the MSP group or the SP group on days 2 and 3 after the start of treatment. The high efficacy of the low dose sulfadoxine/pyrimethamine regimen was the most surprising finding of this study.

No influence of socioeconomic factors on severe malarial anaemia, hyperparasitaemia or reinfection.

Malaria is responsible for nearly 500 million clinical cases per year, only a small proportion of whom will become severely ill. Socioeconomic risk factors may play a role in the development of severe malaria in African children and in their susceptibility to reinfection. In Gabon, 100 children suffering from severe malaria, defined as hyperparasitaemia and/or severe anaemia, were matched for sex, age and provenance to 100 children with mild malaria. Socioeconomic factors were assessed using a standard questionnaire and compared between the 2 groups. The children were followed-up and the time to first reinfection was recorded. No significant influence of socioeconomic factors could be detected on the severity of disease or the time to first reinfection. Socioeconomic factors are not major determinants of severe malarial anaemia and hyperparasitaemia in children in Gabon.

Merozoite surface antigen 1 and 2 genotypes and rosetting of Plasmodium falciparum in severe and mild malaria in Lambaréné, Gabon.

We present a case-control study to investigate the distribution of Plasmodium falciparum genotypes in patients with severe and mild malaria. We compared clinical and parasitological data with the parasites' genotype and rosetting. The study group consisted of 100 children suffering severe malaria, defined as severe anaemia and hyperparasitaemia. These children were matched by age, sex and provenance with 100 children with mild malaria. For characterization of the parasites we used the polymerase chain reaction to determine merozoite surface antigen (MSA) 1 and 2 genotypes and the phenomenon of rosette formation. We found a significant association between rosette formation and disease severity, and a significant association of severe anaemia with the presence of the MSA-1 allele K1. Infections with 2 genotypes in the severely affected group were significantly associated with severe anaemia and the presence of MSA-1 allele K1. Comparison with the findings of other groups led to the conclusion that the occurrence of P. falciparum genotypes seems to differ geographically.

Molecular analysis of recrudescent parasites in a Plasmodium falciparum drug efficacy trial in Gabon.

Recrudescent Plasmodium falciparum parasites were sampled from 108 children taking part in a drug efficacy trial in Gabon. A finger-prick blood sample was taken from each child before treatment, and a post-treatment sample taken of the recrudescent parasites. Sample deoxyribonucleic acid was amplified by the polymerase chain reaction using primers specific to the P. falciparum antigen genes MSP-1, MSP-2 and GLURP. Seventy-seven children had identical parasites in their pre- and post-treatment samples, indicating genuine recrudescences of resistant parasites. Fourteen children had completely different parasites in their pre- and post-treatment samples, indicating either a fresh infection from a mosquito or growth of a population of parasites not detected in the pre-treatment sample, perhaps due to sequestration. The remaining 17 children had a mixture of pre-treatment and new parasites in their post-treatment samples. This study demonstrated the use of polymorphic markers to confirm whether parasites in patients with clinical recrudescences after drug treatment are genuinely resistant.

Parasite antigen-specific interleukin-10 and antibody reponses predict accelerated parasite clearance in Plasmodium falciparum malaria.

Using strict inclusion criteria, we conducted a hospital-based, case-control study in which 100 Gabonese children with severe Plasmodium falciparum malaria were matched for age, gender and provenance with 100 children presenting with mild malaria. Parasite antigen-specific cellular and humoral immunological responses were measured and compared with post-treatment parasite clearance times in each group. Significantly faster parasite clearance times were associated with in vitro production of IL-10 by acute-phase peripheral blood mononuclear cells (PBMC) in response to both liver and asexual stage parasite antigens, but not with proliferative, IFN-gamma, or TNF responses to the same antigens. In addition, in those children with mild malaria, higher levels of acute-phase antibody responses to liver stage antigen-1 (LSA-1) were associated with faster parasite clearance times, and were correlated with the presence of IL-10 responses to the same antigen. No such associations were found for IL-10 or antibody responses to a range of asexual blood stage antigens. Those with severe malaria had significantly lower levels of anti-LSA-1 antibodies compared to their counterparts with mild malaria. In conclusion, the results of this study suggest that parasite antigen-specific IL-10-mediated antibody responses may play a role in the control of asexual stage parasite multiplication in P. falciparum malaria.

Upregulation of ICAM-1, IL-1 and reactive oxygen intermediates (ROI) by exogenous antigens from Plasmodium falciparum parasites in vitro, and of sICAM-1 in the acute phase of malaria.

After 4 hours of stimulation of human mononuclear leukocytes in the presence of 300 ng/ml exogenous Plasmodium falciparum antigens, the ICAM-1 expression increased variably from 15% to 375%. Simultaneously, an increase of IL-1 mRNA production could be observed in Northern blot hybridizations with a specific cDNA gene probe for human IL-1 alpha labelled with digoxigenin. Furthermore, the reactive oxygen intermediates (ROI) production was also found to be enhanced in similar conditions. Additionally, when the levels of soluble ICAM-1 (sICAM-1) in plasma of 122 patients with P. falciparum or Plasmodium vivax malaria were analyzed in an enzyme immunoassay (EIA), significant sICAM-1 increases were found, more pronounced in patients with P. falciparum malaria, in comparison with healthy controls and with the same patients 4 weeks after chemotherapy. The presented results indicate that the expression of ICAM-1 may also be upregulated by exogenous Plasmodium antigens besides cytokines like IL-1 during the acute phase of malaria, with subsequently elevated sICAM-1 concentrations in blood.

[The dual role of tumor necrosis factor (TNF) during a malarial attack]. / Double rôle du tumor necrosis factor (TNF) pendant l'accès palustre.

The roles of the various factors implicated in the pathogenesis of severe malaria are not well understood. Tumor necrosis factor (TNF), a cytokine produced mainly by macrophages, seems to play a crucial role in both the host's defence against the parasite and the development of severe complications. This review investigates the dual role of TNF in acute malaria, summarizing current knowledge of the beneficial and detrimental effects of this molecule. Recent work has suggested a possible explanation for this dualism, involving a complex interaction between TNF and its soluble receptors.

Population lymphocytaire des nourrissons exposés mais non infectés par le VIH à Douala

Introduction. L'objectif de cette étude était de mettre rechercher la présence d'un déficit en cellules T chez le nourrisson exposé non infectés (ENI), l'hypothèse étant que le déficit serait plus marqué lorsque la charge virale maternelle est élevée. Matériels et méthodes. Il s'agit d'une étude transversale analytique menée du 1er décembre 2015 au 08 juin 2016. En phase rétrospective, les données ont été collectées à base d'un questionnaire préétabli. En phase prospective les prélèvements sanguins ont été effectués et les profils immunologiques ont été établis. Les facteurs de transmission du VIH de la mère à l'enfant ont été évalués par régression logistique multi variée. Le test de Hosmer et Lemeshow ont été utilisés pour vérifier l'ajustement du modèle. Résultats. 153 patients répartis en trois groupes dont 60 enfants exposés non infectés, 60 enfants non exposés (NE) et 33 enfants exposés infectés (EI) ont été enrôlés. Les profils immunologiques des enfants NE et ENI ont montré une différence statistiquement significative (P=0,007) pour les taux de CD4. Les profils immunologiques des enfants de la tranche d'âge de 12 à 59 mois d'une part EI et ENI ont montré des différences significatives pour les CD45 (P=0,003), les CD4 (P=0,01), les CD8 (P=0,02). Conclusion. Chez les nourrissons non infectés nés de mères séropositives, plusieurs anomalies immunologiques peuvent être détectées. Ces anomalies pourraient être une conséquence de l'exposition au VIH in utero et en début de vie, et/ou à l'exposition aux médicaments antirétroviraux, ou à la transmission précoce des infections virales persistantes telles que CMV

Facteurs prédictifs de naissance d'un nouveau-né séronégatif issu d'une mère séropositive au VIH à Douala

Introduction. La transmission mère-enfant du VIH constitue le principal mode de contamination chez les enfants âgés de moins de 5 ans. L'introduction de la thérapie antirétrovirale chez les femmes enceintes séropositives, les accouchements par césarienne et l'allaitement artificiel ont réussi à réduire considérablement la transmission verticale du virus de l'immunodéficience humaine. En l'absence de ces mesures préventives, le taux de transmission verticale varie entre 10 à 40%. L'objectif de cette étude est de présenter les facteurs qui prédisposent à la transmission du VIH de la mère à l'enfant à Douala. Matériel et méthodes. Il s'agit d'une étude rétrospective, analytique et transversale menée à l'hôpital du district de Nylon, sur une période de sept mois allant de 01 décembre 2015 au 08 juin 2016. Les données ont été recueillies sur la base d'un questionnaire et les facteurs de transmission du VIH de la mère à l'enfant ont été évalués par régression logistique multi variée. Le test de Hosmer et Lemeshow a été utilisé pour vérifier l'ajustement du modèle. Les différences dans les proportions ont été testées en utilisant le test du chi carré. Les tests de Kruskal-Wallis ont été utilisés pour évaluer les différences globales, puis deux à deux le Mann-Whitney U-tests a été utilisé pour évaluer les différences entre les groupes. Résultats. Au total 157 dossiers de nourrissons ont été enrôlés dans cette étude, parmi eux, 20 étaient infectés par le VIH (P=12%). L'âge moyen au moment du diagnostic était de 4,3±3,6 mois (extrêmes : 1,5 et 16 mois). Les enfants nés avec un poids de moins de 2500 grammes présentaient un risque de TME de 5,6 fois supérieur par rapport à ceux nés avec un poids ≥2500 grammes (OR=5,6 ; IC95% :1,9-16,7). Les enfants qui n'avaient pas reçu de la Névirapine à la naissance (10/15) ont été plus infectés que ceux qui en avaient reçu (10/142) et présentaient un risque de 26,4 fois d'être infectés (OR=26,4 ; IC95% : 7,6-92,3 ; p<0,001). Conclusion. Les délais de mise sous traitement, le stade OMS IV de la maladie, l'alimentation mixte, les CD4 <100/mm3 se présentent comme étant les facteurs prédictifs de TME. Il est donc nécessaire de réduire la charge virale maternelle afin de pouvoir renforcer son système immunitaire et par ailleurs celui de l'enfant en favorisant l'allaitement maternel exclusif

Protection of mice previously infected with Plasmodium vinckei against subsequent Salmonella enteritidis infection is associated with nitric oxide production capacity.

When mice previously cured of a Plasmodium vinckei infection were subsequently infected with Salmonella enteritidis the course of bacterial infection was significantly retarded, showing increased survival duration as compared with control infections in naive mice. Moreover, on stimulation with lipopolysaccharide and/or interferon-gamma, spleen cells from malaria-cured mice showed an increased capacity to produce tumor necrosis factor, interleukin 6, and reactive nitrogen intermediates as compared with spleen cells from naive mice. However, no significant variation in the capacity of spleen cells to release reactive oxygen intermediates was observed between previously malarious and naive mice. The most significant increases were observed in the capacity for reactive nitrogen intermediate production after P. vinckei malaria. These results suggest that the observed protection of mice against salmonellosis in the convalescent phase after malaria may be mediated by nitric oxides.

Deltamethrin impregnated bednets for the control of urban malaria in Kumba Town, South-West Province of Cameroon.

This study was conducted from January to December 1992 in Kumba, a town situated in the rain forest region of the South-West Province of Cameroon, and consisted of a longitudinal survey including parasitological and clinical studies. Forty households were chosen for the study and randomly divided into two groups, each with approximately 240 inhabitants aged < or = 15 years. One group received deltamethrin impregnated bednets and the other group had no nets (control). For the months of April, June and August (rainy season), deltamethrin impregnated bednets did not reduce malaria prevalence significantly, but the overall malaria prevalence for all months of the study was significantly reduced (chi 2 MH = 9.17, P = 0.002). Enlarged spleen rates (chi 2 MH = 6.73, P = 0.009) and spleen sizes (P = 0.0002) were also significantly reduced by the nets. However, the reduction in the geometric mean parasite density (GMPD) was not significant. Even though some of these reductions were statistically significant, they were relatively low in a global context compared with previous work done mainly in rural areas. In an urban environment, parents and children usually stay up late, and probably receive many mosquito bites before going to sleep.

PIP: In 1992, in Cameroon, 40 households in two neighborhoods of Kumba, located in the rain forest region of the South-West Province, were randomly allocated to either the group that received deltamethrin impregnated bednets or the group who received no bednets. Each group had about 240 persons aged 15 years or under. The neighborhoods were Kossala (high malaria prevalence) and Mbonge Road (low prevalence). Parasitological, entomological, and clinical studies were conducted longitudinally so researchers could determine whether deltamethrin impregnated bednets would cause a reduction in malaria morbidity and parasitic indices. The geometric mean parasite density (GMPD) decreased with age, especially for 11-15 year olds, suggesting acquired immunity. The deltamethrin group was more likely than the control group to have lower malaria prevalence (29% vs. 41%; p = 0.002), spleen rates (18.5% vs. 30.4%; p = 0.009), and spleen sizes (p = 0.0002). GMPD was also lower, but not significantly so (764 vs. 1081/mcl). During the rainy season (April, June, and August), malaria prevalence was not statistically significant between the test and control groups. In Kossala, children aged 6-10 years had a higher malaria prevalence rate than other age groups. The deltamethrin impregnated bednets afforded better protection in Mbong Road than in Kossala, suggesting that they are most effective in areas of low malaria endemicity. The significant reductions in human/vector contact were relatively low when compared with earlier studies mainly conducted in rural areas. Parents and children in urban areas such as Kumba tend to stay up late (e.g., watching TV) and probably receive many mosquito bites while awake. Impregnated window curtains may improve protection in malaria endemic urban areas.

Low-dose treatment with sulfadoxine-pyrimethamine combinations selects for drug-resistant Plasmodium falciparum strains.

A total of 252 children were enrolled in a drug trial to assess the effect of minimal doses of sulfadoxine (Sdx) and pyrimethamine (Pyr). Parasite samples isolated from these patients were analyzed before and after treatment to investigate the level of drug-resistant strains. The parasite genes encoding dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) were assayed for point mutations that are associated with resistance against drugs. Before treatment, Pyr(r) genotypes of the DHFR gene were found in 42% of all samples, 8% of the patients harbored a mixed parasite population and 50% had a sensitive DHFR genotype. In terms of the DHPS gene, we found mutations in 45% of the parasites. Twenty-four percent had a Ser(436) mutation, and 26% had a Gly(437) mutation. Recrudescent parasites were highly enriched for both Pyr(r) and Sdx(r) strains after treatment (P < 0.001 and P = 0.029, respectively).

High oxygen radical production is associated with fast parasite clearance in children with Plasmodium falciparum malaria.

It has been hypothesized that reactive oxygen intermediates (ROI) released by leukocytes play a major role in the immune response to many infectious agents. In the present study, the parasitologic and clinical courses of 75 Gabonese children with Plasmodium falciparum malaria were compared with the ability of their granulocytes to produce oxygen radicals. The luminol-dependent chemiluminescence in granulocyte suspensions for the children was measured without stimulation and after stimulation with phorbol-12-myristate-13-acetate, N-formyl-methionyl-leucyl-phenylalanine, or tumor necrosis factor. A significant association was found between fast parasite clearance time and high oxygen radical generation in both the unstimulated and stimulated granulocyte preparations. No correlation was found between fever clearance time and ROI generation. These findings suggest that ROI play a pivotal role in the immune response as a first line of defense against P. falciparum malaria.

Low interleukin-12 activity in severe Plasmodium falciparum malaria.

We compared interleukin-12 (IL-12) and other cytokine activities during and after an acute clinical episode in a matched-pair case-control study of young African children who presented with either mild or severe Plasmodium falciparum malaria. The acute-phase, pretreatment plasma IL-12 and alpha interferon (IFN-alpha) levels, as well as the acute-phase mitogen-stimulated whole-blood production capacity of IL-12, were significantly lower in children with severe rather than mild malaria. IL-12 levels, in addition, showed strong inverse correlations both with parasitemia and with the numbers of circulating malaria pigment-containing neutrophils. Acute-phase plasma tumor necrosis factor (TNF) and IL-10 levels were significantly higher in those with severe malaria, and the concentrations of both of these cytokines were positively correlated both with parasitemia and with the numbers of pigment-containing phagocytes in the blood. Children with severe anemia had the highest levels of TNF in plasma. In all the children, the levels in plasma and production capacities of all cytokines normalized when they were healthy and parasite free. The results indicate that severe but not mild P. falciparum malaria in young, nonimmune African children is characterized by down-regulated IL-12 activity, contrasting markedly with the up-regulation of both TNF and IL-10 in the same children. A combination of disturbed phagocyte functions resulting from hemozoin consumption, along with reduced IFN-gamma responses, may contribute to these differential effects.

The role of red blood cell polymorphisms in resistance and susceptibility to malaria.

In regions highly endemic for Plasmodium falciparum malaria, red cell polymorphisms that confer resistance to severe disease are widespread. Sickle cell trait, alpha-thalassemia, glucose-6-phosphate dehydrogenase deficiency, and blood groups were determined in 100 children from Gabon with severe malaria who were matched with 100 children with mild malaria and followed up for evaluation of reinfections. The sickle cell trait was significantly associated with mild malaria and blood group A with severe malaria. During follow-up, the original severe cases had significantly higher rates of reinfection than the original mild cases, with higher parasitemia and lower hematocrit values. Incidence rates did not differ in the context of erythrocyte polymorphisms, but patients with sickle cell trait presented with markedly lower levels of parasitemia than those without. Thus, the severity of malaria is partly determined by the presence of blood group A and the sickle cell trait. The different presentation of reinfections in severe versus mild cases probably reflects different susceptibility to malaria.