Anopheles gambiae, the major malaria vector in Africa, can be divided into two subgroups based on genetic and ecological criteria. These two subgroups, termed the M and S molecular forms, are ...believed to be incipient species. Although they display differences in the ecological niches they occupy in the field, they are often sympatric and readily hybridize in the laboratory to produce viable and fertile offspring. Evidence for assortative mating in the field was recently reported, but the underlying mechanisms awaited discovery. We studied swarming behaviour of the molecular forms and investigated the role of swarm segregation in mediating assortative mating. Molecular identification of 1145 males collected from 68 swarms in Donéguébougou, Mali, over 2 years revealed a strict pattern of spatial segregation, resulting in almost exclusively monotypic swarms with respect to molecular form. We found evidence of clustering of swarms composed of individuals of a single molecular form within the village. Tethered M and S females were introduced into natural swarms of the M form to verify the existence of possible mate recognition operating within-swarm. Both M and S females were inseminated regardless of their form under these conditions, suggesting no within-mate recognition. We argue that our results provide evidence that swarm spatial segregation strongly contributes to reproductive isolation between the molecular forms in Mali. However this does not exclude the possibility of additional mate recognition operating across the range distribution of the forms. We discuss the importance of spatial segregation in the context of possible geographic variation in mechanisms of reproductive isolation.
Persistence of African anophelines throughout the long dry season (4-8 months) when no surface waters are available remains one of the enduring mysteries of medical entomology. Recent studies ...demonstrated that aestivation (summer diapause) is one mechanism that allows the African malaria mosquito, Anopheles gambiae, to persist in the Sahel. However, migration from distant localities - where reproduction continues year-round - might also be involved.
To assess the contribution of aestivating adults to the buildup of populations in the subsequent wet season, two villages subjected to weekly pyrethrum sprays throughout the dry season were compared with two nearby villages, which were only monitored. If aestivating adults are the main source of the subsequent wet-season population, then the subsequent wet-season density in the treated villages will be lower than in the control villages. Moreover, since virtually only M-form An. gambiae are found during the dry season, the reduction should be specific to the M form, whereas no such difference is predicted for S-form An. gambiae or Anopheles arabiensis. On the other hand, if migrants arriving with the first rain are the main source, no differences between treated and control villages are expected across all members of the An. gambiae complex.
The wet-season density of the M form in treated villages was 30% lower than that in the control (P < 10-4, permutation test), whereas no significant differences were detected in the S form or An. arabiensis.
These results support the hypothesis that the M form persist in the arid Sahel primarily by aestivation, whereas the S form and An. arabiensis rely on migration from distant locations. Implications for malaria control are discussed.
Cet article traite des stratégies d'adaptation développées par les Zinderois pour faire face à la précarité hydrique. À partir d'un travail de terrain qui a permis d'interroger les acteurs ...intervenants dans le secteur d'eau, l'article après une mise en relief de la situation hydraulique de la ville, identifie, analyse et évalue les principales réponses sociales développées par la population pour un accès pérenne à l'eau. Le stockage d'eau, le recours aux forages manuels, aux puits cimentés et aux revendeurs d'eau, la veille hydrique et le recours aux villages environnants dans le cadre d'une solidarité hydraulique sont les principales réponses développées par la population.
Knowledge of the ecological differences between the molecular forms of Anopheles gambiae and their sibling species, An. arabiensis might lead to understanding their unique contribution to disease ...transmission and to better vector control as well as to understanding the evolutionary forces that have separated them.
The distributions of hatching time of eggs of wild An. gambiae and An. arabiensis females were compared in different water types. Early and late hatchers of the S molecular form were compared with respect to their total protein content, sex ratio, development success, developmental time and adult body size.
Overall, the distribution of hatching time was strongly skewed to the right, with 89% of the eggs hatching during the second and third day post oviposition, 10% hatching during the next four days and the remaining 1% hatching over the subsequent week. Slight, but significant differences were found between species and between the molecular forms in all water types. Differences in hatching time distribution were also found among water types (in each species and molecular form), suggesting that the eggs change their hatching time in response to chemical factors in the water. Early hatchers were similar to late hatchers except that they developed faster and produced smaller adults than late hatchers.
Differences in hatching time and speed of development among eggs of the same batch may be adaptive if catastrophic events such as larval site desiccation are not rare and the site's quality is unpredictable. The egg is not passive and its hatching time depends on water factors. Differences in hatching time between species and molecular forms were slight, probably reflecting that conditions in their larval sites are rather similar.
Cet articleexaminela dynamique de la periurbanisationde larrondissement communal IVde la ville de Zinder.Cette periurbanisationconstitue plusieurs enjeux dont entre autres celui du foncier et des ...transformations sociospatiales des villages environnants. La question principale est la suivante : quels sont les enjeux fonciers et la perception de la periurbanisation chez les habitants des villages de larrondissement communal de Zinder IV ? Lobjectif principal est detudier les enjeux fonciers et la perception de la periurbanisation chez les habitants des villages de larrondissement communal de Zinder IV. Pour ce faire, nous avons effectue une analyse bibliographique, des visites dobservation de terrain, des entretiens semi-directifs et une enquete par questionnaire administree aupres de 191 chefs de menage, dans cinq villages periurbains dudit arrondissement. Les resultats obtenus montrent que la periurbanisation a favorise une pression considerable sur les ressources foncieres des villages enquetes et que plus de 90 % de la population pensent que leur village sera rattrape par le phenomene de letalement urbain dans le temps.
The African malaria mosquito, Anopheles gambiae, inhabits diverse environments including dry savannas, where surface waters required for larval development are absent for 4-8 months per year. Under ...such conditions, An. gambiae virtually disappears. Whether populations survive the long dry season by aestivation (a dormant state promoting extended longevity during the summer) or are reestablished by migrants from distant locations where larval sites persist has remained an enigma for over 60 years. Resolving this question is important, because fragile dry season populations may be more susceptible to control. Here, we show unequivocally that An. gambiae aestivates based on a demographic study and a mark release-recapture experiment spanning the period from the end of one wet season to the beginning of the next. During the dry season, An. gambiae was barely detectable in Sahelian villages of Mali. Five days after the first rain, before a new generation of adults could be produced, mosquito abundance surged 10-fold, implying that most mosquitoes were concealed locally until the rain. Four days after the first rain, a marked female An. gambiae s.s. was recaptured. Initially captured, marked, and released at the end of the previous wet season, she has survived the 7-month-long dry season. These results provide evidence that An. gambiae persists throughout the dry season by aestivation and open new questions for mosquito and parasite research. Improved malaria control by targeting aestivating mosquitoes using existing or novel strategies may be possible.
Introduction: Central Nervous System (CNS) malformations usually leave the family in disarray and doctors’ staff powerless. In developed countries, the rigorous application of preventive measures has ...contributed to a significant reduction incidence of these malformations. In African societies, mystical-religious considerations and low socio-economic level contribute to the increased occurrence of these malformations. The purpose of this work was to evaluate the prevalence and management of CNS malformations in our neurosurgical department.
Methods: This was a retrospective study conducted in the neurosurgery department of Yalgado Ouedraogo Teaching Hospital, in Ouagadougou, from 2016 to 2019. All cases of CNS malformations managed in the department with a workable medical record were reviewed.
Results: Five hundred and twenty-four cases were selected. The prevalence of malformations was 7.05%. The mean age of patients was 1.48 years (1 day and 76 years). Thirty-one (5.9%) cases of CNS malformations were diagnosed antenatally. One hundred and twenty-four (23.6%) ultrasounds (including 51 antenatal), 418 CT scans (79.7%) and 9 MRIs (1.7%) were performed. Hydrocephalus (n = 219 (41.7%) and spina bifida (n = 213 (40.6%) were the most common pathologies. Surgical treatment was indicated in 435 cases (83%) of which 179 (41.1%) could be operated. After a follow-up of 15.8 months, there were 46.3% sequelae identified.
Conclusion: CNS malformations are common in our context. They are not always prone to be treated surgically and are at the origin of many neurological sequelae and lifelong disability. Hence there is an urgent need to focus on improving preventive measures in Sub-Saharan Africa.
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