[Histologic kidney lesions during pure nephrotic syndrome in adults in Conakry]. / Lesions histologiques renales au cours du syndrome nephrotique pur de l'adulte a Conakry.

INTRODUCTION: Nephrotic syndrome represents a significant part of chronic kidney disease in Black Africa. Our work aimed to determine the frequency and type of kidney lesions in an adult carrying pure nephrotic syndrome. PATIENTS AND METHODS: We conducted a prospective and descriptive study (2003-2004), 40 patients were recruited on the basis of the presence of a pure nephrotic syndrome. Proteinuria was plentiful, selective to albumin greater than 3 g/24h, not accompanied by hematuria, or high blood pressure, or kidney failure. Cases of bacterial, parasitic and viral infections (hepatitis B, C, HIV) were excluded. By following contra-indications of renal biopsy, samples were taken under local anesthesia by means of percutaneous lumbar and fixed in two tubes, one containing "Michel's medium" and the other 12% Formalin. These techniques and readings were carried out in the pathological anatomy Laboratories of Nantes (France) and Conakry (Guinea). RESULTS: There were 24 men and 16 women with an average age of 26.2 ± 8 years [range: 20-51]. Clinical symptoms were dominated by weight gain characterized by edema. Proteinuria was between 3-3.5 g/24h in 16 (40%); between 3.6-5 g in 2 cases (5%) and greater than 5 g/24h in 22 cases (55%). The number of glomeruli was on average 11 ± 9 [range: 3-36]; glomerular permeability was on average 10.4 ± 10. Renal impairment was glomerular in 22 cases, tubulointerstitial in 12 cases and vascular in 6 cases. Immunofixation was positive in 30/40 cases for IgA IgG IgM; in 26 cases for C1q C3; in 4 cases for C1q C3 C4; and finally for fibrin in 28 cases. Histological renal lesions were FSGS (40%), MDC (35%), MGN (5%), MPGN (5%) and undetermined (15%). CONCLUSION: A regular practice of renal anatomopathological examination "on the spot" will lead us to carefully assess the causes of kidney failure associated with nephrotic syndrome.

INTRODUCTION: Le syndrome néphrotique représente une part importante d'insuffisance rénale chronique en Afrique noire. Notre travail avait pour but de déterminer la fréquence et le type de lésions histologiques rénales chez un adulte porteur d'un syndrome néphrotique pur. PATIENTS ET MÉTHODES: Au cours d'une étude prospective et descriptive (2003­2004), 40 patients ont été sélectionnés sur la base de la présence d'un syndrome néphrotique pur. La protéinurie était abondante, sélective à l'albumine, supérieure à 3 g/24h, non accompagnée d'hématurie, ni d'hypertension artérielle, ni d'insuffisance rénale. Les cas d'infections bactériennes, parasitaires et virales (hépatites B, C, HIV) ont été volontiers exclus. En respectant les contre indications de la biopsie rénale, les prélèvements ont été effectués sous anesthésie locale, par voie lombaire percutanée, puis fixés dans deux tubes dont un contenait du « liquide de Michel ¼ et l'autre du Formol à 12%. Les techniques et lectures ont été effectuées aux Laboratoires d'anatomie pathologique de Conakry (Guinée) et de Nantes (France). RESULTATS: Il s'agissait de 24 hommes et de 16 femmes âgés en moyenne de 26,2 ± 8 ans [20­51]. La symptomatologie clinique était dominée par une prise de poids marquée par les œdèmes. La protéinurie était comprise entre 3­3,5 g/24h dans 16 cas (40%); entre 3,6­5 g dans 2 cas (5%) et supérieure à 5 g/24h dans 22 cas (55%). Le nombre de glomérules était en moyenne de 11 ± 9 [3­36]; la perméabilité des glomérules était en moyenne de 10,4 ± 10. L'atteinte rénale était glomérulaire dans 22 cas, tubulo-interstitielle dans 12 cas et vasculaire dans 6 cas. L' immunofixation a été positive dans 30 cas /40 pour les IgA IgG IgM; dans 26 cas pour C1q C3; dans 4 cas pour C1q C3 C4; et en fin pour la fibrine dans 28 cas. Les lésions histologiques rénales étaient une HSF (40%), une LGM (35%), une GEM (5%), une GNMP (5%) et indéterminée (15%). CONCLUSION: Une pratique régulière de l'examen anatomo-pathologique rénal «sur place" nous amènerait à apprécier judicieusement les causes d'insuffisance rénale en rapport avec un syndrome néphrotique.

[Etiological orientation from the analysis morphological and constitutional of urinary stones in Conakry]. / Orientation etiologique a partir de l'analyse morphologique et constitutionnelle des lithiases urinaires a Conakry.

INTRODUCTION: The epidemiological profile of urinary stones varies from region of the world to another according to food habit and certain enviromental factors. The aim of our study was to establish an etiological approach of the urinary lithiasis collected in Conakry by morphological and constitutional analysis. MATERIALS AND METHODS: It was a prospective study from january 1 rst 2003 to january 1 rst 2004 concerning all the stones collected. They were analysed by binocular magnifying glass and infra red spectrophotometry of Fourier. RESULTS: During the period, 18 patients were observed (14 male, 4 femele) of 27.4 +/- 4 years old (from 2 to 69) living mainly in urban environment. From these patients 28 stones were collected; 12 spontaneously and 16 surgicaly. Their composition were whewellite (36%), struvite (29%), carbapatite (14%), urates (14%) and weddellite (7%). In Conakry stones come mainly from hyperoxaluria and urinary tract infection; hypercalciuria is uncomon. CONCLUSION: The urinary calculations examined among patients show in the adult a prevalence of elements in favour of a hyperoxalurie and a notable context of urinary infections in particular in the child; the pure hypercalciurie remains negligible in Conakry, we plan to lead a thorough work to the national scales.

The spatial distribution of Anopheles gambiae sensu stricto and An. arabiensis (Diptera: Culicidae) in Mali.

Variations in the biology and ecology and the high level of genetic polymorphism of malaria vectors in Africa highlight the value of mapping their spatial distribution to enhance successful implementation of integrated vector management. The objective of this study was to collate data on the relative frequencies of Anopheles gambiae s.s. and An. arabiensis mosquitoes in Mali, to assess their association with climate and environmental covariates, and to produce maps of their spatial distribution. Bayesian geostatistical logistic regression models were fitted to identify environmental determinants of the relative frequencies of An. gambiae s.s. and An. arabiensis species and to produce smooth maps of their geographical distribution. The frequency of An. arabiensis was positively associated with the normalized difference vegetation index, the soil water storage index, the maximum temperature and the distance to water bodies. It was negatively associated with the minimum temperature and rainfall. The predicted map suggests that, in West Africa, An. arabiensis is concentrated in the drier savannah areas, while An. gambiae s.s. prefers the southern savannah and land along the rivers, particularly the inner delta of Niger. Because the insecticide knockdown resistance (kdr) gene is reported only in An. gambiae s.s. in Mali, the maps provide valuable information for vector control. They may also be useful for planning future implementation of malaria control by genetically manipulated mosquitoes.

[Dyslipidemia in uremic patients at the National Hospital of Donka-Conakry]. / Profil lipidique des urémiques a l'Hôptal National de Donka à Conakry.

The prevalence of the dyslipidemia is higher at the patients in chronic renal failure (CRF) than in the general population. The objective of this study was to determine the prevalence and the lipidic anomalies among uraemic patients and to evaluate the others associated factors of cardiovascular risk. The study was descriptive with prospective recruitment (November 2004-June 2005); concerned 60 patients having an advanced chronic renal failure whose calculated clearance of creatinin was lower than 30 ml/mn as well as the hemodialysed patients. The lipidic disturbances on the whole 9/16 dialysed (56%) and 31 uraermia /44 were not dialysed (70%). This majority triglyceride dyslipidemia comprised 8 cases of hypertriglyceridemia in the group of dialysed patients against 19 in the group of not dialysed; 1 case of mixed hyperlipidemia against 6 cases and 4 cases of hypercholesterolemia HDL in the non dialysed group with 1 case of HDL low cholesterol. The patients with dyslipidemia were 4 females (25%) and 5 males (31%) among dialysed group; and of 13 female (29%) and 18 male (41%) among not dialysed. The average age was of 54.3 +/- 0.7 years for dialysed against the 46.6 +/- 0.2 years for the dyslipidémia in the non dialysed. Among others factors of cardiovascular risk, the arterial high blood pressure was noted at 9 dialysed patient's dyslipidémia and 20 case / 31 to the not dialysed dyslipidémia; and the diabetes was observed in 1 and 3 cases respectively. The addiction to smoking was noted in both groups except at the dialysis patients not dyalipidémiques.

[Renal diseases--morbidity and mortality in Nephrology Service, National Hospital Donka]. / Morbidite et mortalite hospitalieres dans le Service de Nephrologie de l'Hopital National Donka.

It is a retrospective study of descriptive type on a 4 years period, from April 1, 1999 to March 31, 2003. The aim was to determine factors bound to morbidity and mortality of renal affections in the Conakry University Hospital Center Nephrology Unit. The study was based on 606 hospitalized patients of whom 21 dialysed. The study's references were age, sex, renal affections frequency, mortality, associated pathologies, hospitalization period, death hours and other factors of cardio-vascular risks (tobacco, alcohol). Patients having answered to the selection criteria were 365 men (60.23%) and 241 women (39.77%) with a sex ratio of 1.51. The average age was 44 +/- 17 years old with extremes of 15 and 95 years old; 16.34% of the patients were aged less than 25 years and 14.03% were more than 65 years old. According to the charge taking, 462 (76.24%) were at their neighbors' charge, only 144 (23.76%) could take themselves in charge for their medical care. According to the received treatment before hospitalization, 357 had consumed decoctions of leaves and roots, 86 consulted a health center. The average period of hospitalization was 13 +/- 9 days with extremes of 1 and 80 days. Nicotine addiction was observed with 183 patients of whom 181 were men and alcoholism with 134 patients of whom 122 were men. Renal affections were chronic renal failure (51%), arterial hypertension (30.36%), chronic kidney disease (8.09%), intense renal failure (7.59%), urinary infections (1.65%), intense kidney disease (0.99%) and kidney cancer (0.33%). Among them, 130 deaths were observed (21.45%). According to the period going on before the medical check up, 24 death occurred 2 weeks after the first symptom, and 106 after more than a month. Considering the hours, 33 death (25.38%) occurred between 8 a.m. and 4 p.m. and 63 deaths (48.47%) between 4 p.m. and 8 a.m.; in 34 cases, the hour was not specified. Mortality was due to chronic renal failure in 97 cases (74.61%), to arterial hypertension in 19 cases (14.62%) and to other affections in 14 cases (0.77%). Infections, diabetes, arterial hypertension and anemia sickle cells were renal risk factors. Morbidity and mortality factors were numerous and varied: medical check up delay, traditional cure, patients 'weak turnover, lack of medical care, lack of required equipment and the absence of popular health education.

Morbidité et mortalité hospitalières dans le service de nephrologie de l'Hôpital National Donka

Il s'agit d'une étude rétrospective de type descriptif sur une période de 4 ans, allant du 01Avril 1999 au 31 Mars 2003. L'objectif était de déterminer les facteurs liés à la morbidité et à la mortalité des affections rénales dans le service de Néphrologie du CHU de Conakry. L'étude a portésur 606 patients hospitalisés dont 21 dialysés. Les paramètres de l'étude étaient l'âge, le sexe, lafréquence des affections rénales, la mortalité, les pathologies associées, le délai de consultation, laprise en charge, le traitement reçu avant l'hospitalisation, la durée d'hospitalisation, les horaires de décès et certains facteurs de risque cardio-vasculaires (tabac, alcool). Les malades ayant réponduaux critères de sélection étaient 365 hommes (60,23%) et 241 femmes (39,77%) avec un sex-ratio de1,51. La moyenne d'âge était de 44 ± 17 ans avec des extrêmes de 15 et 95 ans ; 16,34% des patients étaient âgés de moins de 25 ans et 14,03% avaient plus de 65 ans. Selon la prise en charge, 462 (76,24%) étaient à la charge de leur entourage, seuls 144 (23,76%) pouvaient se prendre en charge pour les soins. Selon le traitement reçu avant l'hospitalisation, 357 avaient consommé des décoctions de feuilles et de racines, 86 avaient consulté un centre de santé. La durée moyenne d'hospitalisation a été de 13 ± 9 jours avec des extrêmes de 1 et 80 jours. Le tabagisme avait été observé chez 183 malades dont 181 hommes et l'alcoolisme chez 134 malades dont 122 hommes. Les affections rénales étaient l'insuffisance rénale chronique (51%), l'hypertension artérielle (30,36%), les glomérulonéphrites chroniques (8,09%), l'insuffisance rénale aiguë (7,59%), les infections urinaires (1,65%) les glomérulonéphrites aiguës (0,99%) et le cancer du rein (0,33%). Parmi eux, 130 décès avaient été observés soit 21,45%. Selon le délai écoulé avant la consultation, 24 décès étaient survenus 2 semaines après le premier symptôme et 106 après plus d'un mois.Suivant les horaires, 33 décès (25,38%) étaient survenus entre 8h et 16h et 63 décès (48,47%) entre 16h et 8h ; dans 34 cas, l'heure n'était pas précisée. La mortalité était due à l'insuffisance rénale chronique dans 97 cas, soit 74,61%, à l'hypertension artérielle dans 19 cas, soit 14,62% et aux autres affections dans 14 cas, soit 0,77%. Les infections, le diabète, l'hypertension artérielle et la drépanocytose étaient les facteurs de risque rénal. Les facteurs de morbidité et de mortalité étaient nombreux et variés à savoir : le retard à la consultation, le traitement traditionnel, le faiblerevenu des malades, l'absence de couverture sanitaire, le manque de prise en charge correct au cours des gardes, le manque d'équipement adéquat et l'absence d'éducation sanitaire populaire

[Dermatologic manifestations associated with immune reconstitution syndrome in HIV+ patients starting HAART: a retrospective study in French Guiana]. / Manifestations dermatologiques associées au syndrome de restauration immunitaire du patient VIH+ débutant un traitement antirétroviral: etude rétrospective en Guyane française.

Immune reconstitution syndrome (IRIS) is an unusual inflammatory reaction to an opportunistic infection in an HIV-positive patient. This syndrome occurs when immunity is restored in the first months of an effective highly active antiretroviral treatment (HAART). First, we described all patients with a cutaneous form of IRIS. Then, between 1992 and 2004 we conducted a retrospective cohort study comparing Herpes Zoster and Herpes Simplex infections among untreated patients, patients treated by HAART for < or = six months, and patients treated for > six months. We observed three cases of atypical leprosy and three original observations: two of these were fistulisation of lymph node histoplasmosis and tuberculosis, the third one reports the recurrence of a treated cutaneous leishmaniasis. Multivariate analysis showed that, after controlling for age, sex and CD4 counts, patients receiving HAART for < or = six months were more likely to develop Herpes Zoster or herpes simplex infections (p < 0.005). Herpes Simplex and Herpes Zoster infections are the two most frequent dermatological manifestations in our tropical setting. Although mycobacterial infections are more rarely observed than in visceral IRIS, the increased incidence of leprosy may be quite significant when the availability of HAART spreads to developing countries.

[Determination of risk factors of smear-negative pulmonary tuberculosis]. / Etude des facteurs de risque de survenue d'une tuberculose pulmonaire a bacilloscopie negative.

OBJECTIVES: to compare the epidemiological, clinical and paraclinical features of smear-negative pulmonary tuberculosis (PT-) and the smear-positive pulmonary tuberculosis (PT+), to determine the risk factors of smear-negative pulmonary tuberculosis. PATIENTS AND METHODS: It was a prospective study, conducted from November 1995 to November 1996. Data were analysed by EPI-INFO 6.04 (OMS/CDC). RESULTS: The study included 426 patients with pulmonary tuberculosis. Among them, 348 (81.7%) were PT+ and 78 (18.3%) were PT-. The sex-ratio was 2.4. Age group of 26 to 45 years was more affected (58.4% for the PT+ and 52.6% for the PT-). The prevalence of HIV infection was statistically higher in PT- (p = 0.01). Cough, sputum and lung condensation syndrom were more observed in PT+ group (p = 0.01). PT- patients had best nutritional status (p = 0.01). The chest X-ray showed more cavitations in the PT+ group (p = 0.000). While, in the PT- group, extra pulmonary lesions as pleural fluid were more frequent (p = 0.02). The full blood count found an anaemia (Hb=9 g/dl) associated to a neutrophilic h yperleucocytosis and an increased e rythrocyte sedimentation at the first hour in the both groups, without significant differance. The rates of CD4, CD8 lymphocytes and the ratio CD4/CD8 were in the normal range. Negative skin tuberculin test was more found in PT- (p = 0.04). The culture of sputum for PT- patients was positive in 15 patients out of 23 (65.2%). CONCLUSION: The risk factors of PT- identified are: Age >45 years, HIV infected patients, no expectoration, no or inefficient cough, no cavitations at the Chest X-ray.

Role of lipopeptides produced by Bacillus subtilis GA1 in the reduction of grey mould disease caused by Botrytis cinerea on apple.

AIM: Test of Bacillus subtilis strain GA1 for its potential to control grey mould disease of apple caused by Botrytis cinerea. METHODS AND RESULTS: GA1 was first tested for its ability to antagonize in vitro the growth of a wide variety of plant pathogenic fungi responsible for diseases of economical importance. The potential of strain GA1 to reduce post-harvest infection caused by B. cinerea was tested on apples by treating artificially wounded fruits with endospore suspensions. Strain GA1 was very effective at reducing disease incidence during the first 5 days following pathogen inoculation and a 80% protection level was maintained over the next 10 days. Treatment of fruits with an extract of GA1 culture supernatant also exerted a strong preventive effect on the development of grey mould. Further analysis of this extract revealed that strain GA1 produces a wide variety of antifungal lipopeptide isomers from the iturin, fengycin and surfactin families. A strong evidence for the involvement of such compounds in disease reduction arose from the recovery of fengycins from protected fruit sites colonized by bacterial cells. CONCLUSIONS: The results presented here demonstrate that, despite unfavourable pH, B. subtilis endospores inoculated on apple pulp can readily germinate allowing significant cell populations to establish and efficient in vivo synthesis of lipopeptides which could be related to grey mould reduction. SIGNIFICANCE AND IMPACT OF THE STUDY: This work enables for the first time to correlate the strong protective effect of a particular B. subtilis strain against grey mould with in situ production of fengycins in infected sites of apple fruits.

Semipermeable species boundaries between Anopheles gambiae and Anopheles arabiensis: evidence from multilocus DNA sequence variation.

Attempts to reconstruct the phylogenetic history of the Anopheles gambiae cryptic species complex have yielded strongly conflicting results. In particular, An. gambiae, the primary African malaria vector, is variously placed as a sister taxon to either Anopheles arabiensis or Anopheles merus. The recent divergence times for members of this complex complicate phylogenetic analysis, making it difficult to unambiguously implicate interspecific gene flow, versus retained ancestral polymorphism, as the source of conflict. Using sequences at four unlinked loci, which were determined from multiple specimens within each of five species in the complex, we found contrasting patterns of sequence divergence between the X chromosome and the autosomes. The isolation model of speciation assumes a lack of gene flow between species since their separation. This model could not be rejected for An. gambiae and An. arabiensis, although the data fit the model poorly. On the other hand, evidence from gene trees supports genetic introgression of chromosome 2 inversions between An. gambiae and An. arabiensis, and also points to more broad scale genetic exchange of autosomal sequences between this species pair. That such exchange has been relatively recent is suggested not only by the lack of fixed differences at three autosomal loci but also by the sharing of full haplotypes at two of the three loci, which is in contrast to several fixed differences and considerably deeper divergence on the X. The proposed acquisition by An. gambiae of sequences from the more arid-adapted An. arabiensis may have contributed to the spread and ecological dominance of this malaria vector.

The pyrethroid knock-down resistance gene in the Anopheles gambiae complex in Mali and further indication of incipient speciation within An. gambiae s.s.

In Mali the Anopheles gambiae complex consists of An. arabiensis and Mopti, Savanna and Bamako chromosomal forms of An. gambiae s.s. Previous chromosomal data suggests a complete reproductive isolation among these forms. Sequence analysis of rDNA regions led to the characterization of two molecular forms of An. gambiae, named M-form and S-form, which in Mali correspond to Mopti and to Savanna/Bamako, respectively, while it has failed so far to show any molecular difference between Savanna and Bamako. The population structure of An. gambiae s.l. was analysed in three villages in the Bamako and Sikasso areas of Mali and the frequency of pyrethroid resistance of the knock-down resistance (kdr) type was calculated. The results show that the kdr allele is associated only with the Savanna form populations and absent in sympatric and synchronous populations of Bamako, Mopti and An. arabiensis. This is the first molecular indication of barriers to gene flow between the Bamako and Savanna chromosomal forms. Moreover, analyses of specimens collected in the Bamako area in 1987 show that the kdr allele was already present in the Savanna population at that time, and that the frequency of this allele has gradually increased since then.

The phenology of malaria mosquitoes in irrigated rice fields in Mali.

A field study was carried out in the large-scale rice irrigation scheme of the Office du Niger in Mali to investigate the relation between anopheline mosquito larval development and small-scale differences in irrigation practices, such as water level, irrigation application and irrigation frequency. The objective of the study was to find out if water management can be used as a tool for vector control to reduce the malaria transmission risk. Larvae of Anopheles gambiae s.s.,; the main malaria vector in the study area, developed mostly in the first 6 weeks after transplanting the rice. During rice development, a succession of anopheline species was observed. This was associated with a marked decrease in light intensity reaching the water surface as plant height increased. Minor differences in water management resulted in noticeable variations in larval densities and species composition. A. gambiae s.s. larvae were most abundant during the early growing stages and almost absent in a closed rice crop. Due to improper drainage after harvest, A. gambiae s.s. breeding was soon re-established in fields where small pools of water were retained. The results suggest that larval mosquito habitats in the Office du Niger can be significantly reduced by water management, simultaneous planting and harvesting and proper drainage of fallow fields.

[Epidemiology of malaria in a village of Sudanese savannah area in Mali (Bancoumana). 2. Entomo-parasitological and clinical study ]. / Epidémiologie du paludisme dans un village de savane soudanienne du Mali (Bancoumana). 2. Etude entomo-parasitologique et clinique.

We carried out five cross sectional surveys between 1993 and 1994 to assess the epidemiology of malaria in the village of Bancoumana, located in the Sudanese savannah areas of Mali. Each survey included a collection of entomological, clinical, parasitological and immunological data. The study population involved 1600 children from six months to 9 years of age. The main vector was Anopheles gambiae s.l., man bite rate and entomological inoculation rate were maximum respectively in August (peak of the transmission season) and October (end of transmission season). Plasmodium. falciparum was the main parasite species observed. Spleen enlargement rate, parasite rate, gametocyte rate and parasite density varied significantly with age and season. The parasite rate, gametocyte rate and parasite density were significantly low in October 1994 compared with October 1993 while the entomologic parameter did not show any variation over the two years. This reduction of parasitologic index between 1993 and 1994 may be related to an increase of anti-malarial drug use in the population. Our results show that malaria is hyperendemic in the village of Bancoumana.

Genetic differentiation of Anopheles gambiae s.s. populations in Mali, West Africa, using microsatellite loci.

Anopheles gambiae sensu stricto is a principal vector of malaria through much of sub-Saharan Africa, where this disease is a major cause of morbidity and mortality in human populations. Accordingly, population sizes and gene flow in this species have received special attention, as these parameters are important in attempts to control malaria by impacting its mosquito vector. Past measures of genetic differentiation have sometimes yielded conflicting results, in some cases suggesting that gene flow is extensive over vast distances (6000 km) and is disrupted only by major geological disturbances and/or barriers. Using microsatellite DNA loci from populations in Mali, West Africa, we measured genetic differentiation over uniform habitats favorable to the species across distances ranging from 62 to 536 km. Gene flow was strongly correlated with distance (r(2) = 0.77), with no major differences among chromosomes. We conclude that in this part of Africa, at least, genetic differentiation for microsatellite DNA loci is consistent with traditional models of isolation by distance.

Behavioural determinants of gene flow in malaria vector populations: Anopheles gambiae males select large females as mates.

BACKGROUND: Plasmodium-refractory mosquitoes are being rapidly developed for malaria control but will only succeed if they can successfully compete for mates when released into the wild. Pre-copulatory behavioural traits maintain genetic population structure in wild mosquito populations and mating barriers have foiled previous attempts to control malaria vectors through sterile male release. METHODS: Varying numbers of virgin male and female Anopheles gambiae Giles, from two strains of different innate sizes, were allowed to mate under standardized conditions in laboratory cages, following which, the insemination status, oviposition success and egg batch size of each female was assessed. The influence of male and female numbers, strain combination and female size were determined using logistic regression, correlation analysis and a simple mechanistic model of male competition for females. RESULTS: Male An. gambiae select females on the basis of size because of much greater fecundity among large females. Even under conditions where large numbers of males must compete for a smaller number of females, the largest females are more likely to become inseminated, to successfully oviposit and to produce large egg batches. CONCLUSIONS: Sexual selection, on the basis of size, could either promote or limit the spread of malaria-refractory genes into wild populations and needs to be considered in the continued development and eventual release of transgenic vectors. Fundamental studies of behavioural ecology in malaria vectors such as An. gambiae can have important implications for malaria control and should be prioritised for more extensive investigation in the future.