Residual malaria transmission: Magnitude and drivers of persistent Plasmodium infections despite high coverage of control interventions in Burkina Faso, West Africa.

This study collected baseline data on malaria vectors to characterize the drivers and the factors of persistent malaria transmission in two villages in the western part of Burkina Faso. Mosquitoes were collected in each village using the Human landing catch and pyrethrum spray catch and identified using the morphological keys. Molecular analyses were performed for the identification of An. gambiae complex species, the detection of Plasmodium infection and kdr-995F mutation. Anopheles mosquito larvae were also collected in the same villages, reared to adult's stage for the WHO tube and cone tests performing. The physical integrity of the LLINs already used by people in each village was assessed using the proportional hole index (pHI). An. gambiae s.l. was the main malaria vector accounting for 79.82% (5560/6965) of all collected mosquitoes. The biting pattern of An. gambiae s.l. was almost constant during the survey with an early aggressiveness before 8 p.m. and later biting activity after 6 a.m. The EIR varied from 0.13 to 2.55 infected bites per human per night (average: 1.03 infected bites per human per night). An. gambiae s.l. populations were full susceptible to Chlorpyrifos-methyl (0.4%) and Malathion (5%) with high kdr-995F mutation frequencies (>0.8). The physical integrity assessment showed high proportion of good nets in Santidougou compared to those collected in Kimidougou. This study highlighted a persistence of malaria transmission despite the intense use of vector control tools as LLINs and IRS by correlating mosquito biting time and human behavior. It provided a baseline guide for the monitoring of the residual malaria transmission in sub-Saharan Africa and encouraging the development of new alternative strategies to support the current malaria control tools.

Epidemiological evaluation of onchocerciasis along Ogun River System, southwest Nigeria.

BACKGROUND & OBJECTIVE: Epidemiological studies were carried out to assess the prevalence and community microfilarial load (CMFL) of onchocerciasis after repeated annual treatment with ivermectin along Ogun river System, southwest Nigeria. METHOD: Skin snips were taken from consented participants in 11 selected communities along the River system. The microfilarial load of the community was estimated. RESULTS: The prevalence and CMFL varied significantly in the communities (p <0.05). The prevalence of onchocerciasis ranged from 19.1 to 45.6%, while the CMFL ranged from 0.11 to 1.03 microfilariae per skin snip. The CMFL recorded was <5 microfilariae per skin snip, i.e. recognized by WHO as threshold value in certifying the communities to be free of onchocerciasis as public health problem, thus, signifying the possibility of onchocerciasis elimination in the study area. CONCLUSION: Efforts should therefore be intensified to achieve improved ivermectin coverage and compliance in annual ivermectin treatment in order to completely eliminate onchocerciasis as a public health problem in the studied communities.

[Effectiveness of a polymerase chain reaction using seminested and multiplex strategy for the identification of the three main bacteria responsible for meningitis in Burkina Faso]. / Efficacité d'une technique de réaction de polymérisation en chaîne (seminested et multiplex) pour l'identification des trois principales espèces bactériennes responsables de méningites au Burkina Faso.

A prospective study (from August 2006 to April 2007) was carried out with 214 cerebrospinal fluid samples with suspicion of bacterial meningitis. The aim of the study was to assess the effectiveness of the simultaneous detection of Neisseria meningitidis, Streptococcus sp. and Haemophilus influenzae using seminested polymerase chain reaction strategy. Among the 214 samples tested by both PCR and culture, the overall confirmation rate was 64% for PCR and 40.1% for culture (P = 2 x 10⁻6). Taking culture method as the standard reference, the overall sensitivity of PCR was 98.8% and specificity, 59.4%. The sensitivity of PCR was 100, 97.3 and 100% respectively for N. meningitidis, Streptococcus sp. and H. influenzae with respective specificities of 70, 93.2 and 97.2%. In conclusion, the seminested PCR strategy is a sensitive method and it can be implemented in the reference public health laboratories for an exhaustive microbiological surveillance of bacterial meningitis.

[Main characteristics of the street food sector in Bobo-Dioulasso, Burkina Faso]. / Caractéistiques de l'alimentation de rue dans la ville de Bobo-Dioulasso, Burkina Faso.

To investigate the sector of food sold in the streets of Bobo-Dioulasso and identify relevant information for action, a survey on knowledge and practices of street food vendors and consumers was conducted in June 2005. Data have been collected in 928 street food selling posts. Structured questionnaires were used to collect data from 874 street vendors and 2474 consumers. Street food sites are concentrated in places where administration and trade activities are usually running. The street food seller is a married and illiterate woman of 32 years old. Cereals (48.5%), meat (33.9%), milk (9.6%) and fruits (4.4%) are the basic consumables. The street food consumer is a non married man, 27 years old working in profit-making activity. Consumers use many criteria to choose the place to eat, at times or permanently. The street food sector represents a source of income and induces change in household eating habits. Street food in Bobo-Dioulasso needs to be better organised, by using an holistic approach that involves all the actors.

Year to year and seasonal variations in vector bionomics and malaria transmission in a humid savannah village in west Burkina Faso.

A longitudinal entomological study was carried out from 1999 to 2001 in Lena, a humid savannah village in the western region of Burkina Faso in order to establish malaria vector bionomics and the dynamics of malaria transmission. In the first year, malaria transmission was mainly due to An. gambiae s.s., but during the two later years was due to An. funestus, which were observed in high frequency towards the end of the rainy season. PCR identification of samples of An. gambiae s.1. showed 93% to be An. gambiae s.s. and 7% An. arabiensis. An. funestus constituting more than 60% of the vectors were identified in PCR as An. funestus s.s. The persistence of intense vectorial activity in this village was probably due to the road building in a swampy area creating a semi-permanent swamp that provided large sites for larval mosquitoes. These swampy sites seemed to be more favorable for An. funestus than for An. gambiae s.s. Thus, land development must be monitored and subjected to planning to minimize vector proliferation. Such a system of planning could lead to the restriction or even elimination of the swamp that is the source of larvae developing in the heart of the village.

[Influence of social perceptions and practices on the use of bednets in the malaria control programme in Ivory Coast (West Africa)]. / Representations sociales et pratiques liées à l'utilisation des moustiquaires dans la lutte contre le paludisme en Côte d'Ivoire (Afrique de l'Ouest).

The National Malaria Programme in Ivory Coast has encountered difficulty in winning public acceptance of insecticide-treated bednets. We speculate that resistance to the use of bednets could be rooted in social perceptions, beliefs and practices in the communities. The purpose of this study was to identify sociocultural and environmental factors that could be used to support promotion strategies and acceptance of impregnated bednets in Ivory Coast. Survey findings confirmed that bednets were not in widespread use among the population (25%). The most widely used methods were burning mosquito coils (50%) and indoor spraying (31%). Use of impregnated bednets was low (6%). Most survey respondents (73%) indicated initial appreciation for the effectiveness of bednets in protecting against mosquitoes as a nuisance. However only 9% of respondents thought that impregnated bednets provided protection against malaria although they did not necessarily use them. Design was a determinant factor for the use, and even acceptance, of bednets. The population want rectangular, permanently impregnated bednets large enough to accommodate at least 2 persons. Cost was a major obstacle to wider use by the population. According to our data the best price for the population would be between 2000 and 2500 FCFA as compared to the current price of 3500 FCFA in Ivory Coast.

Representations sociales et pratiques liees a l'utilisation des moustiquaires dans la lutte contre le paludisme en Cote d'Ivoire (Afrique de l'Ouest)

Devant les difficultes que rencontre le Programme National de Lutte contre le Paludisme (PNLP) de Cote d'Ivoire; dans sa volonte d'amener les populations a adopter les moustiquaires impregnees d'insecticide; nous nous sommes demandes si les representations sociales; les attitudes et les pratiques des communautes liees a l'utilisation des moustiquaires n'expliquent pas cette contre-performance. Notre etude a eu pour but de documenter les facteurs socioculturels et environnementaux pour renforcer les strategies de promotion et de vulgarisation de la moustiquaire impregnee en Cote d'Ivoire. Les resultats obtenus montrent qu'au niveau des enquetes quantitatives; la moustiquaire en general est faiblement utilisee par les populations (25). Les moyens les plus utilises sont les serpentins fumigenes (50) et les bombes aerosols (31). La moustiquaire impregnee est tres faiblement utilisee (6). La moustiquaire est; de maniere generale; appreciee dans un premier temps pour son efficacite dans la protection contre les nuisances dues aux moustiques par 73des enquetes. Seulement 9de ces enquetes pensent que la moustiquaire impregnee sert a se proteger contre le paludisme; mais ne l'utilisent pas necessairement. L'organisation des unites de couchage; voire leur inadaptation; sont determinantes dans l'utilisation de la moustiquaire. La moustiquaire souhaitee par les populations est celle d'au moins 2 places; de forme rectangulaire; de couleur blanche; faite en tulle a mailles fines; transparente; impregnee d'insecticide et a impregnation definitive. Toutefois; son cout semble etre le handicap majeur a son adoption par les populations; pour qui le cout ideal de la moustiquaire a l'achat; se situe entre 2000 et 2500 FCFA contre les 3 500 Frs actuellement pratiques en Cote d'Ivoire

The current status of onchocerciasis in the forest/savanna transition zone of Côte d'Ivoire.

Onchocerca volvulus exists in at least two strains in West Africa, while its black-fly vectors consist of sibling species, dwelling in the savanna and forest/transition zones. In transition and degraded forest zones both parasite strains and different sibling species of the vector can be sympatric. The strain of parasite in infected humans and in vector black-flies was determined in two bioclimes along the Bandama river of Côte d'Ivoire. The upper Bandama is located in the savanna bioclime while the Middle Bandama is located in a degraded forest zone. At both sites, savanna-dwelling sibling species of the Simulium damnosum sensu lato species complex predominated. The severe-strain of O. volvulus was the predominant strain at both sites. However, severe-strain parasites represented a significantly larger proportion of those found in the vector population than in the human population in the degraded forest of the Middle Bandama. These data suggest that in degraded forest areas recently invaded by savanna-dwelling species of S. damnosunz s.l. transmission of the severe-strain of the parasite might be more efficient than transmission of the mild-strain.

Detection of Onchocerca volvulus infection in low prevalence areas: a comparison of three diagnostic methods.

The standard assay for onchocerciasis diagnosis is microscopical detection of microfilariae in skin snips. Skin snipping is painful, requires appropriate sterilization of equipment, and may fail to diagnose light infections. Two alternatives are a polymerase chain reaction (PCR) test which detects parasite DNA in pieces or scrapings of skin and a test based on allergic reactions to topical application of diethylcarbamazine (DEC). We compared these 2 diagnostics with standard skin snip microscopy in 313 individuals from 2 villages in Guinea, with low prevalence after over 10 years of control by the Onchocerciasis Control Programme. Lower and upper bounds on sensitivities and specificities of these 3 tests were estimated. In addition, these parameters were estimated using 5 different statistical models. Where prevalence was low, PCR and the DEC patch test appeared to be more sensitive than skin snipping which has low sensitivity. As the DEC test is non-invasive, simple and cheap, it may provide a good alternative to skin snipping alone for surveillance in low prevalence areas.

[Human onchocerciasis and "sowda" in the Republic of Yemen]. / Onchocercoses humaines et "sowda" en République du Yémen.

The geophysics of the north Yemen, associating a north-south directed mountainous fish bone (rising in more of 2,000 meters), to numerous rivers or "wadis" is convenient to the development of simulium shelters, main vectors for cutaneous filariasis to Onchocerca sp. Following several missions of bio-clinical and epidemiological evaluations in neighbouring villages of wadis, it has been possible to study different clinical aspects: one reminding the classical african onchocerciasis with generalized and diffused dermatitis, and, on an other hand, a hyperreactive dermatitis on one side of the body and associated with a collateral lymphatic ganglion. This disease is well known for local populations as "aswad" meaning "black" or "sowda". Clinically whatever the studied focus, coexists the two types of onchodermatitis (uni or bilateral). Yhe sowda patients are proportionally less numerous than those touched by the generalized type. Frequent eye lesions of the West African onchocerciasis are not found in sowda cases. In classical optical microscopy, microfilaria is morphologically indifferenciable between sowda and onchocerciasis clinical aspects. Skin snips were carried out on patients of both groups. Identification of microfilaria by molecular biology through the study of the DNA genome was done out of 5 skin snips. Microfilaria was kept dry between laminas and the DNA extracted from rehydrated microfilaria. DNA was intensified with specific primers of Onchocerca type (O150PCR). This phase was followed by hybridisation of amplification products by PCR to specific stains: OVS-2 for Onchocerca volvulus species, OCH for Onchocerca ochengi, PFS1 and PSS1-BT respectively for the forest strain and the savannah strain of Onchocerca volvulus as described previously. We can distinguish 2 kinds of answers based on the clinical origin of the snip-tests: the first one concern 3 patients with numerous dermal microfilariae but without any clinical sowda and corresponding to microfilaria O. volvulus type but different from the forest or savannah strains found in sub-Saharan Africa. The second one corresponds to 2 patients with less than 5 microfilaria in their snip-test. They show the typical clinical picture of sowda. They are identified as microfilaria type Onchocerca but they do not belong to species volvulus, or to species ochengi. It seems quite probable that the clinical picture of sowda be the result of developing onchocerciasis of animal origin and not identified as to day. The ivermectin, therapeutic of choice for African onchocerciasis in annual unique cure seems less effective in the coverage of sowda. In that case rehearsal of cures every 3 months would be necessary for mass campaigns to limit the transmission of this filariasis.

Topical application of diethylcarbamazine to detect onchocerciasis recrudescence in west Africa.

The Onchocerciasis Control Programme in West Africa (OCP) has succeeded in eliminating blinding onchocerciasis as a public health problem throughout much of West Africa. The efforts of the OCP are now turning towards surveillance, with the goal of rapidly detecting and controlling outbreaks of infection in the onchocerciasis-free zone. With this goal in mind, cutaneous application of a solution of diethylcarbamazine (the DEC-patch test) was evaluated in 1996-99 as a method to detect patent Onchocerca volvulus infection in children and adolescents, a sentinel population for the detection of recrudescence. In an analysis of 1887 individuals in Côte d'Ivoire and Burkina Faso, the DEC-patch test produced prevalence estimates comparable to those obtained by skin snip. The sensitivity of the DEC-patch assay was marginally greater in children and adolescents than in adults, and was greater in individuals who had received prior Mectizan treatment. These data suggest that the DEC-patch test may be a useful tool for detecting recrudescence of O. volvulus infection in a sentinel population of children and young adults within the onchocerciasis-free zone created by the OCP.

Eotaxin expression in Onchocerca volvulus-induced dermatitis after topical application of diethylcarbamazine.

In persons with onchocerciasis, topical application of the anthelminthic diethylcarbamazine (DEC) induces clinical and histologic responses similar to acute papular onchodermatitis, including recruitment of eosinophils to the skin. To determine whether the eosinophil chemokine eotaxin is likely to be associated with eosinophil recruitment in onchodermatitis, DEC was applied to a 5-cm2 area on the skin of infected persons, and biopsies were taken from lesions 24 h later. Histologic analysis showed elevated dermal and epidermal eosinophils compared with tissue from an adjacent (untreated) site. Reverse transcription-polymerase chain reaction showed that eotaxin gene expression in DEC-treated skin was elevated 2- to 17-fold compared with control tissue. Eotaxin immunoreactivity was noted in mononuclear cells and eosinophils in the perivascular region of the dermis and in lymphatic and vascular endothelial cells. Together, these observations are consistent with a role for eotaxin in recruitment of eosinophils to the dermis in early stage onchocercal skin disease.

Pool screen polymerase chain reaction for estimating the prevalence of Onchocerca volvulus infection in Simulium damnosum sensu lato: results of a field trial in an area subject to successful vector control.

Detection of infective parasites in the vector population can be an early indicator of recrudescence in areas freed of new cases of onchocerciasis. However, dissection of vector black flies is inefficient in areas subject to effective control. Recently, a polymerase chain reaction (PCR)-based assay has been used to detect a single Onchocerca volvulus-infected black fly in pools containing large numbers of uninfected flies. This method had not been validated on wild-caught black flies in an area subject to effective vector control. Here, we report a method of restricting the pool screen PCR assay to infectious parasites and the results of a field test in an area subject to long-term vector control. The prevalence of infection determined by dissection did not differ from that determined by pool screen PCR. The results suggest that the PCR assay may be a useful tool for epidemiologic surveillance for 0. volvulus infection.

Diagnostics in onchocerciasis: future challenges.

The classical method of determining the prevalence and intensity of onchocercal infection is by the demonstration and counting of microfilariae in biopsies obtained by skin snipping. Although very specific, this technique is inadequate for detecting early, light or prepatent infections, and is also becoming increasingly unacceptable to the populations investigated. The prolonged clearing effect that Mectizan (ivermectin, MSD) treatment has on skin microfilariae also renders the skin-snip method of diagnosis less appropriate in areas with Mectizan treatment. Given all these factors, the greater challenge in the area of diagnostics for onchocerciasis is to develop a less invasive, adequately sensitive, and equally specific diagnostic test, either to replace or to be an adjunct to the present skin-snip method. This challenge is being addressed, with at least three new diagnostic tests for onchocerciasis under development: an immunological assay, based on a three-antigen cocktail; a PCR-based assay, which may also be used for 'pool screening' of blackflies; and the diethylcarbamazine (DEC) patch test. Of all these tests, the DEC patch test seems to fit best the criteria of an ideal test. The PCR assay would be better than the patch test if the cost of using it could be reduced substantially.

Detection of Onchocerca volvulus infection by O-150 polymerase chain reaction analysis of skin scratches.

The standard assay for onchocerciasis diagnosis is microscopic detection of parasites in skin snips. Skin snipping is painful and may potentially transmit bloodborne infections. Thus, an alternative method for the diagnosis of onchocerciasis that does not require skin snipping is needed. A polymerase chain reaction (PCR)-based assay was shown to detect the presence of parasite DNA in superficial skin scrapings. Detection of parasite DNA in both skin snips and skin scratches was found to be more sensitive for detecting low-density infections than was microscopic examination of skin snips. The skin scratch PCR assay is minimally invasive and painless and does not present the risk of transmitting bloodborne infections. These properties make the skin scratch an attractive alternative to the skin snip for detecting O. volvulus infection.

[A case of cross infection by Onchocerca volvulus and Onchocerca ochengi in Simulium damnosum S.L]. / Un cas d'infectivite mixte par onchocerca volvulus et Onchocerca ochengi chez Simulium damnosum S.L.

During a routine entomological survey conducted within the framework of the Program to Control Onchocerciasis in West Africa, a female simulium forest fly was found to be contaminated by 13 Onchocerca volvulus larvae and 7 Onchocerca ochengi larvae. The two Onchocerca species were identified using specific DNA probes. We speculate that cross infection could be related either to behavioral factors, e.g. interruption of blood meals on two different hosts, or developmental factors, e.g. asynchronous development of parasites of the same species or specific differences in the duration of parasite cycles. Further study will be needed to determine the incidence and scope of cross infection in areas where accurate assessment of the impact of vector control on transmission of onchocerciasis in man is required.

Vector-parasite transmission complexes for onchocerciasis in West Africa.

BACKGROUND: In West Africa, there are two strains of the filarial parasite Onchocerca volvulus, which differ in their ability to induce ocular disease. Transmission studies have suggested that six sibling species of the parasite vector, the black fly Simulium damnosum sensu lato, allow development of the two strains of O volvulus with varying efficiency. We aimed to test the hypothesis of parasite-vector complexes, whereby the two parasite strains, known as forest and savanna, are preferentially transmitted by distinct groups of the species of S damnosum S l. METHODS: During 1993 and 1994, wild black flies were collected from 11 river basins within the area covered by the Onchocerciasis Control Programme (OCP). The flies were dissected and filarial larvae, ovaries, and malpighian tubules removed. Genomic DNA was extracted from larvae, and PCR amplification was used to classify O volvulus parasites as forest or savanna strains. PCR-amplified DNA from ovaries and malpighian tubules was used to distinguish sibling species of S damnosum s l. S yahense and S squamosum were distinguished by body colour. FINDINGS: 214 of 105105 flies dissected were infected with filarial larvae; 84 of these were infected with mature O volvulus parasites. Of the 35 savanna-dwelling infected flies. 17 carried forest-strain parasites and 18 savanna-strain parasites. Of the 45 infected flies identified as the forest dwelling sibling species. 20 carried savanna-strain parasites and 25 forest-strain parasites. No significant differences were found in the numbers of mature larvae of each strain carried by the forest-dwelling species of fly or in the number of forest and savanna larvae in savanna-dwelling vector species. INTERPRETATION: Vector-parasite transmission complexes do not currently play a part in the biology of O volvulus transmission in the area of the OCP in West Africa. This finding has important strategic implications for the future of efforts to control onchocerciasis in West Africa.

Onchocerca volvulus: comparison of field collection methods for the preservation of parasite and vector samples for PCR analysis.

In recent years, methods for the identification of the filarial worm Onchocerca volvulus and its vector, blackflies of the Simulium damnosum complex (S. damnosum sensu lato (s.l.)), based on the amplification of parasite and vector DNA sequences with the polymerase chain reaction (PCR), have been developed. Routine application of these methods requires techniques for sample collection and preservation that are compatible with the limitations of field collection, yet preserve DNA in a form suitable for PCR. Two different methods for sample preservation were evaluated by the field collection teams and the DNA probe laboratory of the Onchocerciasis Control Programme in West Africa. The most successful involved the preservation of material from O. volvulus and its associated vectors in a dried state on microscope slides. Of over 1200 parasite samples preserved in this manner, more than 93% retained DNA yielding positive results in PCR analysis (1208/1291). Vector material (malpighian tubules and ovaries) preserved in the same manner on the same microscope slides also yielded DNA that was suitable for PCR.