Stéphanie Dos Santos

Asymptomatic Carriage of Plasmodium in Urban Dakar: The Risk of Malaria Should Not Be Underestimated

Introduction The objective of this study was to measure the rate of asymptomatic carriage of plasmodium in the Dakar region two years after the implementation of new strategies in clinical malaria management. Methodology Between October and December 2008, 2952 households selected in 50 sites of Dakar area, were visited for interviews and blood sampling. Giemsa-stained thick blood smears (TBS) were performed for microscopy in asymptomatic adult women and children aged 2 to 10 years. To ensure the quality of the microscopy, we performed a polymerase chain reaction (PCR) with real time qPCR in all positive TBS by microscopy and in a sample of negative TBS and filter paper blood spots. Results The analysis has concerned 2427 women and 2231 children. The mean age of the women was 35.6 years. The mean age of the children was 5.4 years. The parasite prevalence was 2.01% (49/2427) in women and 2.15% (48/2231) in children. Parasite prevalence varied from one study site to another, ranging from 0 to 7.41%. In multivariate analysis, reporting a malaria episode in 2008 was associated with plasmodium carriage (OR = 2.57, P = 0.002) in women; in children, a malaria episode (OR = 6.19, P<0.001) and a travel out of Dakar during last 3 months (OR = 2.27, P = 0.023) were associated with plasmodium carriage. Among the positive TBS, 95.8% (93/97) were positive by plasmodium PCR. Among the negative TBS, 13.9% (41/293) were positive by PCR. In blood spots, 15.2% (76/500) were positive by PCR. We estimated at 16.5% the parasite prevalence if PCR were performed in 4658 TBS. Conclusion Parasite prevalence in Dakar area seemed to be higher than the rate found by microscopy. PCR may be the best tool for measuring plasmodium prevalence in the context of low transmission. Environmental conditions play a major role in the heterogeneity of parasite prevalence within sites.

IgG responses to the gSG6-P1 salivary peptide for evaluating human exposure to Anopheles bites in urban areas of Dakar region, Sénégal

BackgroundUrban malaria can be a serious public health problem in Africa. Human-landing catches of mosquitoes, a standard entomological method to assess human exposure to malaria vector bites, can lack sensitivity in areas where exposure is low. A simple and highly sensitive tool could be a complementary indicator for evaluating malaria exposure in such epidemiological contexts. The human antibody response to the specific Anopheles gSG6-P1 salivary peptide have been described as an adequate tool biomarker for a reliable assessment of human exposure level to Anopheles bites. The aim of this study was to use this biomarker to evaluate the human exposure to Anopheles mosquito bites in urban settings of Dakar (Senegal), one of the largest cities in West Africa, where Anopheles biting rates and malaria transmission are supposed to be low.MethodsOne cross-sectional study concerning 1,010 (505 households) children (n = 505) and adults (n = 505) living in 16 districts of downtown Dakar and its suburbs was performed from October to December 2008. The IgG responses to gSG6-P1 peptide have been assessed and compared to entomological data obtained in or near the same district.ResultsConsiderable individual variations in anti-gSG6-P1 IgG levels were observed between and within districts. In spite of this individual heterogeneity, the median level of specific IgG and the percentage of immune responders differed significantly between districts. A positive and significant association was observed between the exposure levels to Anopheles gambiae bites, estimated by classical entomological methods, and the median IgG levels or the percentage of immune responders measuring the contact between human populations and Anopheles mosquitoes. Interestingly, immunological parameters seemed to better discriminate the exposure level to Anopheles bites between different exposure groups of districts.ConclusionsSpecific human IgG responses to gSG6-P1 peptide biomarker represent, at the population and individual levels, a credible new alternative tool to assess accurately the heterogeneity of exposure level to Anopheles bites and malaria risk in low urban transmission areas. The development of such biomarker tool would be particularly relevant for mapping and monitoring malaria risk and for measuring the efficiency of vector control strategies in these specific settings.

Evaluation of the effectiveness of malaria vector control measures in urban settings of Dakar by a specific anopheles salivary biomarker.

Standard entomological methods for evaluating the impact of vector control lack sensitivity in low-malaria-risk areas. The detection of human IgG specific to Anopheles gSG6-P1 salivary antigen reflects a direct measure of human–vector contact. This study aimed to assess the effectiveness of a range of vector control measures (VCMs) in urban settings by using this biomarker approach. The study was conducted from October to December 2008 on 2,774 residents of 45 districts of urban Dakar. IgG responses to gSG6-P1 and the use of malaria VCMs highly varied between districts. At the district level, specific IgG levels significantly increased with age and decreased with season and with VCM use. The use of insecticide-treated nets, by drastically reducing specific IgG levels, was by far the most efficient VCM regardless of age, season or exposure level to mosquito bites. The use of spray bombs was also associated with a significant reduction of specific IgG levels, whereas the use of mosquito coils or electric fans/air conditioning did not show a significant effect. Human IgG response to gSG6-P1 as biomarker of vector exposure represents a reliable alternative for accurately assessing the effectiveness of malaria VCM in low-malaria-risk areas. This biomarker tool could be especially relevant for malaria control monitoring and surveillance programmes in low-exposure/low-transmission settings.

Water-related factors and childhood diarrhoea in African informal settlements. A cross-sectional study in Ouagadougou (Burkina Faso)

Improved access to water is a key factor in reducing diarrhoeal diseases, a leading cause of death among children in sub-Saharan Africa. In terms of water access, sub-Saharan African cities are some of the worst off in the world, with 20% of populations supplied by an unimproved water source. This situation is even worse in informal settlement areas. Using cross-sectional data on access to water from a survey implemented in three informal neighbourhoods of the Ouagadougou Health and Demographic Surveillance System, logistic regressions are modelled to test the effect of different modalities of access to water on childhood diarrhoea. Our results show that the prevalence of diarrhoea in children is high: one-third of households with a child under 10 experienced an episode of childhood diarrhoea during the 2 weeks preceding the survey, even though 91% of the households surveyed have access to an improved water source. The results show that efforts to reduce childhood morbidity would be greatly enhanced by strengthening piped water access in informal settlement areas in Africa. In addition, this study confirms that, beyond the single measure of the main access to water, accurate variables that assess the accessibility to water are needed.

Perceived malaria in the population of an urban setting: a skipped reality in Dakar, Senegal.

BackgroundUrban malaria remains a public health problem. Dakar is located in a low endemic area. However, anti-malarial drugs consumption is reported to be high despite the decline of malaria announced by health authorities. The objective of the present study was to assess the burden of reported malaria attacks (RMAs) in 2008 and to describe care-seeking behaviours in the population of Dakar, Senegal.MethodsIn this cross-sectional study, 2,952 households selected from 50 sites were visited. In each household, a women and a child between two and 10 years old were interviewed about a malaria episode that occurred in 2008. The following information was recorded: age, education level, sex (for children), type of care seeking, method of diagnosis, use of anti-malarial treatment, place of medication purchase, bed net use, malaria-related deaths in the family, and perceptions of the frequency of mosquito bites. After a description of the variables in each subsample, a Pearson’s chi-square test was used to compare proportions, and logistic regression was performed to identify the association between RMAs and other covariates.ResultsAmong women, 31.8% reported a malaria attack in 2008; among children, the rate of malaria attacks reported by mothers or caretakers was 39.0%. With regard to care-seeking, 79.5% of women and 81.5% of children with a RMA had visited health facilities (HFs). Younger women and children under five years old were more likely to visit a HF (P<0.001). Presumptive diagnosis was the primary method that was used to identify malaria in HFs. For those who had visited a HF, the rate of anti-malarial treatment was 77% in women and 60% in children. Finally, 43.6% of women and 42.0% of children declared the use of bed nets. In a multivariate analysis, the malaria-related death of a relative and perceptions of mosquito bites were significantly associated with RMAs in women. In children, age was associated with RMAs.ConclusionThe frequent perceptions of the occurrence of malaria in the population were confirmed at the HF by the high presumptive diagnosis of health professionals. Despite the decline of malaria that has been announced by health authorities, the population will continue to complain of malaria and seek care directly at private pharmacies. This situation may sustain the circulation of anti-malarial drugs and increase the risk of an emergence of anti-malarial resistance.

Environmental factors and childhood fever in areas of the ouagadougou health and demographic surveillance system, burkina faso

Using data on 825 under-5 children from the Ouagadougou Health and Demographic Surveillance System collected in 2010, this article examines the effects of aspects of the immediate environment on childhood fever. Logit regression models were estimated to assess the effects of the quality of the local environment on the probability that a child is reported to have had a fever in the two weeks preceding the survey, after controlling for various demographic and socioeconomic variables. While the estimated impact of some environmental factors persisted in the full models, the effects of variables such as access to water and type of household waste management decreased in the presence of demographic, socioeconomic and neighbourhood factors. The management of waste water was found to significantly affect the occurrence of childhood fever. Overall, the results of the study call for more efforts to promote access to tap water to households at prices that are affordable for the local population, where the threats to child health appears to be greatest.