Malaria overdiagnosis and subsequent overconsumption of antimalarial drugs in Angola: Consequences and effects on human health.

Microscopic blood smear examinations done in health centers of Angola demonstrated a large overdiagnosis of malaria cases with an average rate of errors as high as 85%. Overall 83% of patients who received Coartem® had an inappropriate treatment. Overestimated malaria diagnosis was noticed even when specific symptoms were part of the clinical observation, antimalarial treatments being subsequently given. Then, malaria overdiagnosis has three main consequences, (i) the lack of data reliability is of great concern, impeding epidemiological records and evaluation of the actual influence of operations as scheduled by the National Malaria Control Programme; (ii) the large misuse of antimalarial drug can increase the selective pressure for resistant strain and can make a false consideration of drug resistant P. falciparum crisis; and (iii) the need of strengthening national health centers in term of human, with training in microscopy, and equipment resources to improve malaria diagnosis with a large scale use of rapid diagnostic tests associated with thick blood smears, backed up by a "quality control" developed by the national health authorities. Monitoring of malaria cases was done in three Angolan health centers of Alto Liro (Lobito town) and neighbor villages of Cambambi and Asseque (Benguéla Province) to evaluate the real burden of malaria. Carriers of Plasmodium among patients of newly-borne to 14 years old, with or without fever, were analyzed and compared to presumptive malaria cases diagnosed in these health centers. Presumptive malaria cases were diagnosed six times more than the positive thick blood smears done on the same children. In Alto Liro health center, the percentage of diagnosis error reached 98%, while in Cambambi and Asseque it was of 79% and 78% respectively. The percentage of confirmed malaria cases was significantly higher during the dry (20.2%) than the rainy (13.2%) season. These observations in three peripheral health centers confirmed what has already been noticed in other malaria endemic regions, and highlight the need for an accurate evaluation of the Malaria control programme implemented in Angola.

Field evaluation of rapid diagnostic tests for malaria in Yaounde, Cameroon.

Rapid diagnostic tests (RDTs) are affordable, alternative diagnostic tools. The present study aimed to evaluate RDTs available in Cameroon and compare their characteristics to follow the parasitological response of patients for 28 days. Malaria diagnosis was assessed in 179 febrile patients using conventional microscopy as the reference method. Parascreen detects both Plasmodium falciparum-specific histidine-rich protein 2 (Pf HRP-2) and Pan-specific plasmodial lactate dehydrogenase (pLDH) in all four human Plasmodium spp. Diaspot is based on the detection of Pf HRP-2. OptiMAL-IT (pLDH specific for P. falciparum and pLDH for all four human Plasmodium spp.) was assessed for comparison. The reliability of RDTs was evaluated by calculating the sensitivity, specificity, positive predictive value, negative predictive value, false-positive rate, false-negative rate, and likelihood ratio. The clinical outcome of 18 children treated with atovaquone-proguanil and followed for 28 days was evaluated using microscopy and RDTs. Of 179 samples, 133 (74.3%) were pure P. falciparum-positive smears, 4 (2.2%) pure P. malariae-positive smears, and 42 (23.5%) negative smears. Parascreen and Diaspot had high sensitivity (>92%) and positive predictive values (>94%). The specificities for Parascreen and Diaspot were 81.0% and 90.5%, respectively. The false-positive rates and the false-negative rates were 19.0% and 4.5% for Parascreen and 9.5% and 8.3% for Diaspot, respectively. Most false-negatives occurred in samples with low parasitaemia (<500 asexual parasites/µL). The performance of RDTs was better at higher parasitaemia (>500 asexual parasites/µL). Four pure P. malariae were only detected by the pan-Plasmodium bands of Parascreen and OptiMAL-IT. In blood samples from patients treated and followed-up for 28 days, HRP2-based RDTs remained positive in most samples until Day 28. Despite negative smears, OptiMAL-IT remained positive in several patients until Day 7 but was negative in all patients from Day 14 onwards. RDTs can improve the management of febrile patients. The validity, ease of use, and cost of HRP2-based tests were comparable. However, one of the current weaknesses of the RDT-based strategy using the tests available in Cameroon is inadequate sensitivity for low parasitaemia. In some cases, RDT results may require correct interpretation based on clinical history, clinical examination, and microscopic diagnosis.

Human antibody response to Anopheles saliva for comparing the efficacy of three malaria vector control methods in Balombo, Angola.

Human antibody (Ab) response to Anopheles whole saliva, used as biomarker of Anopheles exposure, was investigated over a period of two years (2008-2009), in children between 2 to 9 years old, before and after the introduction of three different malaria vector control methods; deltamethrin treated long lasting impregnated nets (LLIN) and insecticide treated plastic sheeting (ITPS)--Zero Fly®) (ITPS-ZF), deltamethrin impregnated Durable (Wall) Lining (ITPS-DL--Zerovector®) alone, and indoor residual spraying (IRS) with lambdacyhalothrin alone. These different vector control methods resulted in considerable decreases in all three entomological (82.4%), parasitological (54.8%) and immunological criteria analyzed. The highest reductions in the number of Anopheles collected and number of positive blood smears, respectively 82.1% and 58.3%, were found in Capango and Canjala where LLIN and ITPS-ZF were implemented. The immunological data based on the level of anti-saliva IgG Ab in children of all villages dropped significantly from 2008 to 2009, except in Chissequele. These results indicated that these three vector control methods significantly reduced malaria infections amongst the children studied and IRS significantly reduced the human-Anopheles contact. The number of Anopheles, positive blood smears, and the levels of anti-saliva IgG Ab were most reduced when LLIN and ITPS-ZF were used in combination, compared to the use of one vector control method alone, either ITPS-DL or IRS. Therefore, as a combination of two vector control methods is significantly more effective than one control method only, this control strategy should be further developed at a more global scale.

Human antibody responses to the Anopheles salivary gSG6-P1 peptide: a novel tool for evaluating the efficacy of ITNs in malaria vector control.

To optimize malaria control, WHO has prioritised the need for new indicators to evaluate the efficacy of malaria vector control strategies. The gSG6-P1 peptide from gSG6 protein of Anopheles gambiae salivary glands was previously designed as a specific salivary sequence of malaria vector species. It was shown that the quantification of human antibody (Ab) responses to Anopheles salivary proteins in general and especially to the gSG6-P1 peptide was a pertinent biomarker of human exposure to Anopheles. The present objective was to validate this indicator in the evaluation of the efficacy of Insecticide Treated Nets (ITNs). A longitudinal evaluation, including parasitological, entomological and immunological assessments, was conducted on children and adults from a malaria-endemic area before and after the introduction of ITNs. Significant decrease of anti-gSG6-P1 IgG response was observed just after the efficient ITNs use. Interestingly, specific IgG Ab level was especially pertinent to evaluate a short-time period of ITNs efficacy and at individual level. However, specific IgG rose back up within four months as correct ITN use waned. IgG responses to one salivary peptide could constitute a reliable biomarker for the evaluation of ITN efficacy, at short- and long-term use, and provide a valuable tool in malaria vector control based on a real measurement of human-vector contact.

Human antibody response to Anopheles gambiae saliva: an immuno-epidemiological biomarker to evaluate the efficacy of insecticide-treated nets in malaria vector control.

For the fight against malaria, the World Health Organization (WHO) has emphasized the need for indicators to evaluate the efficacy of vector-control strategies. This study investigates a potential immunological marker, based on human antibody responses to Anopheles saliva, as a new indicator to evaluate the efficacy of insecticide-treated nets (ITNs). Parasitological, entomological, and immunological assessments were carried out in children and adults from a malaria-endemic region of Angola before and after the introduction of ITNs. Immunoglobulin G (IgG) levels to An. gambiae saliva were positively associated with the intensity of An. gambiae exposure and malaria infection. A significant decrease in the anti-saliva IgG response was observed after the introduction of ITNs, and this was associated with a drop in parasite load. This study represents the first stage in the development of a new indicator to evaluate the efficacy of malaria vector-control strategies, which could apply in other arthropod vector-borne diseases.

Efficacy of non-artemisinin- and artemisinin-based combination therapies for uncomplicated falciparum malaria in Cameroon.

BACKGROUND: The use of drug combinations, including non-artemisinin-based and artemisinin-based combination therapy (ACT), is a novel strategy that enhances therapeutic efficacy and delays the emergence of multidrug-resistant Plasmodium falciparum. Its use is strongly recommended in most sub-Saharan African countries, namely Cameroon, where resistance to chloroquine is widespread and antifolate resistance is emerging. METHODS: Studies were conducted in Cameroonian children with acute uncomplicated P. falciparum malaria according to the standard World Health Organization protocol at four sentinel sites between 2003 and 2007. A total of 1,401 children were enrolled, of whom 1,337 were assigned to randomized studies and 64 were included in a single non-randomized study. The proportions of adequate clinical and parasitological response (PCR-uncorrected on day 14 and PCR-corrected on day 28) were the primary endpoints to evaluate treatment efficacy on day 14 and day 28. The relative effectiveness of drug combinations was compared by a multi-treatment Bayesian random-effect meta-analysis. FINDINGS: The results based on the meta-analysis suggested that artesunate-amodiaquine (AS-AQ) is as effective as other drugs (artesunate-sulphadoxine-pyrimethamine [AS-SP], artesunate-chlorproguanil-dapsone [AS-CD], artesunate-mefloquine [AS-MQ], dihydroartemisinin-piperaquine [DH-PP], artemether-lumefantrine [AM-LM], amodiaquine, and amodiaquine-sulphadoxine-pyrimethamine [AQ-SP]). AM-LM appeared to be the most effective with no treatment failure due to recrudescence, closely followed by DH-PP. CONCLUSION: Although AM-LM requires six doses, rather than three doses for other artemisinin-based combinations, it has potential advantages over other forms of ACT. Further studies are needed to evaluate the clinical efficacy and tolerance of these combinations in different epidemiological context.

Antimalarial drug use in general populations of tropical Africa.

BACKGROUND: The burden of Plasmodium falciparum malaria has worsened because of the emergence of chloroquine resistance. Antimalarial drug use and drug pressure are critical factors contributing to the selection and spread of resistance. The present study explores the geographical, socio-economic and behavioural factors associated with the use of antimalarial drugs in Africa. METHODS: The presence of chloroquine (CQ), pyrimethamine (PYR) and other antimalarial drugs has been evaluated by immuno-capture and high-performance liquid chromatography in the urine samples of 3,052 children (2-9 y), randomly drawn in 2003 from the general populations at 30 sites in Senegal (10), Burkina-Faso (10) and Cameroon (10). Questionnaires have been administered to the parents of sampled children and to a random sample of households in each site. The presence of CQ in urine was analysed as dependent variable according to individual and site characteristics using a random - effect logistic regression model to take into account the interdependency of observations made within the same site. RESULTS: According to the sites, the prevalence rates of CQ and PYR ranged from 9% to 91% and from 0% to 21%, respectively. In multivariate analysis, the presence of CQ in urine was significantly associated with a history of fever during the three days preceding urine sampling (OR = 1.22, p = 0.043), socio-economic level of the population of the sites (OR = 2.74, p = 0.029), age (2-5 y = reference level; 6-9 y OR = 0.76, p = 0.002), prevalence of anti-circumsporozoite protein (CSP) antibodies (low prevalence: reference level; intermediate level OR = 2.47, p = 0.023), proportion of inhabitants who lived in another site one year before (OR = 2.53, p = 0.003), and duration to reach the nearest tarmacked road (duration less than one hour = reference level, duration equal to or more than one hour OR = 0.49, p = 0.019). CONCLUSION: Antimalarial drug pressure varied considerably from one site to another. It was significantly higher in areas with intermediate malaria transmission level and in the most accessible sites. Thus, P. falciparum strains arriving in cross-road sites or in areas with intermediate malaria transmission are exposed to higher drug pressure, which could favour the selection and the spread of drug resistance.