[Mosquitoes, Distribution and Specific Richness in Eight Countries of Africa: Cape Verde, Mauritania, Senegal, Gambia, Mali, Burkina Faso, Niger and Chad]. / Moustiques, Distribution et Richesse Spécifique dans Huit Pays D'afrique: Cap-Vert, Mauritanie, Sénégal, Gambie, Mali, Burkina Faso, Niger et Tchad.

Mosquitoes (Diptera, Culicidae) form a family of insects of considerable public health importance. Mention of their presence/absence was tackled in the literature and by specialized websites for eight African countries: Cape Verde, Mauritania, Senegal, Gambia, Mali, Burkina Faso, Niger and Chad. In total, 216 species have been recorded belonging to 13 genera: Anopheles (48 species), Aedeomyia (2), Aedes (62), Coquillettidia (6), Culex (54), Culiseta (1), Eretmapodites (7), Ficalbia (3), Lutzia (1), Mansonia (2), Mimomyia (7), Toxorhynchites (4) and Uranotaenia (19). The presence of these species in the study area is certain except for three species whose presence is doubtful. This specific richness represents 6% of the world's richness. The countries with the highest specific richness are Burkina Faso (162 species), Senegal (143) and Mali (110); the country with the lowest richness is Cape Verde (11). This richness is lower in the north in hyper-arid climate and higher in the south in sub-humid climate. Chad is the least well inventoried country. All species are considered native, with the exception of Ae. (Stegomyia ) albopictus (the Asian tiger mosquito) introduced in 2016 into Mali and possibly Ae. (Ochlerotatus ) caspius into Mauritania and Ae. (Stg. ) aegypti introduced into Nouakchott, Mauritania. This synthesis of the knowledge may be useful for vector control, public health, and future research.

Distribution and relative densities of Aedes aegypti in Niger.

Its climate and environmental conditions put Niger at particularly high risk of the spread of Aedes mosquitoes, which can transmit arboviruses. In September 2016, the Republic of Niger reported its first outbreak of Rift Valley Fever (RVF) in the northern region of Tahoua, near the Mali border, particularly in the departments of Tchintabaraden, Tassara, and Abalak. The history of RVF has showed that epidemics and epizootics have a considerable socioeconomic impact in affected countries, such as Niger, whose populations are particularly concerned by livestock farming. Cross-sectional studies were conducted to investigate the abundance of Aedes aegypti and the risk of arbovirus transmission in 54 villages between 2002 and 2017. Sampling took place in 27 villages, with three methods used in each village: (a) capture of aggressive female mosquitoes landing on human adult volunteers from three households, both indoors and outdoors, during two consecutive nights ; (b) insecticide spray collections of resting mosquitoes early in the morning in five selected dwellings, different from those chosen for landing catches, and (c) capture by four Centers for Disease Control (CDC) light traps, both indoors and outdoors, for two nights. The remaining 27 villages were sampled only by insecticide spray collection of resting mosquitoes. The inventory, distribution, and abundance of mosquito species found at the sampled localities were evaluated. The mosquitoes (Culicidae) caught belonged to four genera, namely: Anopheles spp., Aedes spp., Culex spp. and Mansonia spp. Besides these Culicidae, other biting Diptera (Phlebotomes) were found during the capture. À total of 130,424 adult mosquitoes was caught during the study, 2.6% (3,444/130,423) of them Aedes spp. Aedes aegypti accounted for 96.6% of the Aedes spp. captured. Ae. Aegypti was collected in 41.0% (22/54) of the villages and was abundant (accounting for more than 15% of all mosquitoes captured) in 5 localities. The presence, geographical distribution, and abundance of Ae. aegypti near and in human habitations suggest a high risk of arbovirus transmission in Niger. The high abundance of arbovirus vectors encountered in this study should be a source of concern. Our observations highlight the importance of quantifying and monitoring the risk of arbovirus transmission in Niger. These results are of great importance for public health.

Longitudinal follow-up of malaria transmission dynamics in two villages in a Sahelian area of Niger during a nationwide insecticide-treated bednet distribution programme.

Malaria transmission was monitored in two villages in the Sahel zone of Niger over 4 years. During this period, a nationwide vector control programme was carried out in which insecticide-treated bednets were distributed free to mothers of children aged <5 years. Anopheles gambiae and Anopheles arabiensis (Diptera: Culicidae) were found to be the major malaria vectors. The dynamics of An. gambiae s.l. did not vary dramatically over the study period although the proportion of female mosquitoes found resting indoors decreased in both villages and, in one village, the parity rate and sporozoite index were significantly reduced after bednet distribution. By contrast with An. gambiae, the dynamics of Anopheles funestus altered greatly after the bednet distribution period, when adult density, endophagous rate and sporozoite rates decreased dramatically. Our observations highlight the importance of quantifying and monitoring the dynamics and infections of malaria vectors during large-scale vector control interventions.

Anopheles hervyi in Niger: no evidence for a role in Plasmodium falciparum transmission.

Anopheles hervyi is an endemic mosquito species with a very limited spatial distribution in the south east of Niger. No new captures have been reported since the 1960s and its role in malaria transmission has not been studied. In the present study, the use of CDC light traps showed it to be much more abundant than previously found but there was no evidence to suggest it was a malaria vector in this region. The larval habitats have not been identified but the potential role of a saline lake in determining the distribution of this species is discussed.

[Focusing of Schistosoma haematobium transmission in irrigated perimeters of the Niger valley (Niger): importance of malacological factors]. / Focalisation de la transmission de Schistosoma haematobium au sein des périmètres irrigués de la vallée du Niger (Niger): importance des facteurs malacologiques.

BACKGROUND: Currently, the control of urinary schistosomiasis is mostly based on mass treatment. Characterization of Schistosoma haematobium transmission could lead to adding new methods to the control strategy. METHODS: We carried out malacological and cercariometrical surveys in irrigated perimeters of the Niger River valley. A semi-monthly follow-up was performed in three main sites of human-water contact in a village located at the border of the irrigated perimeter. Bulinids were collected during 20 min; after identification based on the shell morphology, their parasites were characterized by isoelectrofocalisation. The cercariometrical technique by differential filtration was used to evaluate the density of cercariae in every site with two 20-litre samples of water collected at various periods of the day (9, 12, 15 and 18 h). RESULTS: In the arm of the river, the cercariometry never showed cercariae whereas only some Bulinus truncatus, all negative, were collected. In the channels, B. truncatus and B. globosus were observed and highest density was found during the dry season. Only B. truncatus was naturally infested. Homozygote BB phenotype (characteristic of S. haematobium) was observed in all positive molluscs. Using cercariometry, more than two third of cercariae were collected at 3:00 PM. CONCLUSION: Transmission of S. haematobium was primarily focused in the irrigating channels during the dry hot season at the beginning of afternoon. These results should lead to improve the output of S. haematobium control methods within irrigated areas.

Bulinus forskalii: a new potential intermediate host for Schistosoma haematobium in Niger.

Malacological monitoring of two irrigated areas in Niger highlighted the natural susceptibility of Bulinus forskalii to infection with Schistosoma haematobium when the parasitic load is high. This first report of S. haematobium infection in B. forskalii, which is an abundant snail in irrigated areas, has been confirmed experimentally.

[Experimental infection of goats with Schistosoma bovis and S. curassoni: comparative pathogenic effects]. / Infestation expérimentale de caprins par Schistosoma bovis et S. curassoni: effets pathogènes comparés.

Specific mortality and morbidity have been quantified in goats experimentally infected with Schistosoma bovis or S. curassoni strains from Niger. The study involved nine animals followed during 380 days after infection with, respectively, 1,800 or 2,400 cercariae. S. bovis was significatively more pathogenic than S. curossoni in terms of mortality, weight loss and packed cell volume decrease. In addition, the intensity of clinical symptoms was significatively and positively correlated to the levels of fecal egg excretion. Compared to non-infected controls, a growth differential of, respectively, 1,600 and 880 grams per month should incite to consider S. bovis and S. curassoni as parasites of serious economical impact in sahelian countries.

ELISA study of oocyst-sporozoite transition in malaria vectors.

Intrinsic vector characteristics and environmental factors affect the sporogonic development of P. falciparum in Anopheles mosquitoes. We tested for the presence of the circumsporozoite protein, as a marker of the oocyst to sporozoite transition in naturally infected Anopheles gambiae s.l. and Anopheles funestus. Malaria vectors were collected in a village in the Sahel of Niger during the rainy and dry seasons. ELISA-CSP was carried out on abdomen and head/thorax portions from more than 2000 samples. No significant difference was found in the overall rates of infection of An. gambiae s.l. (4.13%) and An. funestus (3.58%). Given the differences in duration of the two parasite stages, P. falciparum CSP antigen prevalence was nearly as high in the abdomen as in the head/thorax, and did not differ significantly between An. gambiae s.l. and An. funestus. These preliminary results suggest that development from oocysts to salivary gland sporozoites is similar in the two vectors. However, these developmental indices varied as a function of the season in which samples were collected, particularly for An. gambiae s.l. This simple method may be useful for field studies assessing the effect of environmental and genetic factors on parasite survival.

[Heterogeneity of Schistosoma haematobium transmission in irrigated fields]. / Hétérogénéité de la transmission de Schistosoma haematobium dans les périmètres irrigués du Niger.

Heterogeneity of Schistosoma haematobium transmission in irrigated fields. Although irrigated areas exist since a long time in the Niger Valley the distribution of the urinary schistosomiasis does not appear homogeneous, testifying to the existence of limiting or favourable factors. The identification of these factors could lead to a better definition of the distribution of the schistosomiasis risks and to optimise control programmes. The population of five villages about 1,900 inhabitants living in the same irrigated area (Sébéri) was examined at the end of 1999 before treatment and surveyed two and ten months after treatment by praziquantel in order to investigate re-infections. In parallel, the transmission sites were subject to a semi-monthly malacological follow-up from 1998 to 2001 and the water contacts were quantified in the sites of the main village during 2000. Before treatment, schistosomiasis risks appeared related to the proximity between habitat and lateral canals: the infections concerning youngers were all the more intense that the dwellings were close to the canal. The parasitological indices were the highest in the village lacking of other water sources. The morbidity indices followed a similar distribution with maximum values in the children of the 3 villages located to less than 1 km from the canal; however, morbidity was mainly observed in the adult population, in particular male, of the 2 villages which were the most distant from the canal. After treatment, the incidence of the re-infection between 2 and 10 months was comparable in the 3 villages close to the canal (28%) but was significantly weaker in the 2 villages far from the transmission sites (5%). In the villages bordering the canal, the incidence in the children was all the more high since the habitat was close to the canal. Between 1999 and 2000, the collected number of Bulinus truncatus decreased from 1.4 to 0.6 individuals per survey; moreover, no mollusc harbouring parasites was found, representing the decrease of the parasite burden. The abnormal weakness of re-infection, regarding this type of focus, could be explained by the repeated stop of water supply inducing a complete drying out of the canal for 2 months during the year preceding the study. These repeated drying out also resulted in a reduction of the exposure. Whereas the average frequentation of the sites of the canal remained rather comparable between January (cold dry season) and May (dry hot season), it decreased dramatically in September (rainy season but canals were not irrigated this year) from 99 to 11 daily contacts. The use of the lateral canal when filled represented 80% of the contacts. In the event of drying out, 80% of the contacts were transferred in the ponds but not in the river (5% of the contacts whatever the season). These results confirmed (1) that the presence of canals reduced the use of natural sites and (2) that the drying out of the canals induced a total reduction of the contacts.

[Course of urinary schistosomiasis in Niamey, Niger]. / Evolution de la schistosomose urinaire à Niamey, Niger.

A school survey has been carried out in 1998 on a representative sample of 30 schools to assess the effect of the recent urban growth of Niamey on the urban focus of urinary schistosomiasis. A total of 2,024 10-12 years old children were examined and questioned about their water contacts in Niamey and travels in rural areas during the previous year. Generally the prevalence of S. haematobium was low (16%). This can be explained by the lower exposure in urban areas; by the moderate transmission level in the river and by the low incidence of temporary stays in rural areas. A second survey has been carried out in 2000 in 4 schools of a periurban suburb to study the distribution of parasitological risk at the periphery level. A total of 247 10-12 years old children were examined and questioned about their water contacts. Prevalence of S. haematobium was higher in this suburb (74%) but there was a significant decrease of parasitological indices from periphery to the centre. This change seemed related to differences of exposure with an increasing use of water supply and a decreasing use of irrigation canals for swimming and domestic activities.

[Transmission of Schistosoma haematobium in the town of Niamey, Niger]. / Transmission de Schistosoma haematobium dans la ville de Niamey, Niger.

Located in an area where Schistosoma haematobium is hyperendemic, the town of Niamey is a focus of hypoendemicity. The aim of the malacological follow-up studies undertaken over a one year period was the determination of the mollusc species present in the water bodies, the appreciation of their space-time distribution of the snail and to find out the potential seasons of transmission. The investigation applied to 22 sites of transmission in the urban community. Four molluscs species (Bulinus truncatus, B. forskalii, B. globosus and B. senegalensis) are collected. The first three species are present all the year long, with a peak of density in the dry season. The last species (B. senegalensis) is found only during the rainy season. B truncatus and B. senegalensis are the two naturally infested species. The main site of transmission is the river Niger. The ponds play a secondary role in the peripheral districts. The main intermediate host of S. haematobium is B. truncatus.

Recent urban growth and urinary schistosomiasis in Niamey, Niger.

A cluster sample survey was conducted in 1998 in 30 schools to assess the effect of the growth of Niamey during the last decade on a urinary schistosomiasis urban focus described in 1989. Two thousand and forty-two children (11.0 + 0.1 years old) had a urine filtration test and answered a behavioural questionnaire. Snail populations of the sites used by schoolchildren were followed up in 1999. The global prevalence was 15.7% in 1998, as opposed to 23.7% in 1989. The prevalence was very low in schools far from the river and higher in those along the Niger banks, particularly in villages on the periphery of the urban area. Geographical factors were more important than socio-economic ones in explaining the distribution of the disease. Only 46% of the children in Niamey reported water contact; mainly in the river, rarely in pools and the canal. The infection risk was low in pools (RR = 1.6), high in the river (RR = 3.5) and very high in the canal (RR = 12.5). Malacological studies confirmed the location of transmission sites obtained through parasitological studies and the questionnaire. Sixty-one per cent of the children travelled outside Niamey to the hyperendemic surrounding areas. However, these movements did not increase their infection level. The results are discussed in relation to water contact behaviour and Schistosoma haematobium transmission features.

Microsatellites and the genetics of highly selfing populations in the freshwater snail Bulinus truncatus.

Hermaphrodite tropical freshwater snails provide a good opportunity to study the effects of mating system and genetic drift on population genetic structure because they are self-fertile and they occupy transient patchily distributed habitats (ponds). Up to now the lack of detectable allozyme polymorphism prevented any intrapopulation studies. In this paper, we examine the consequences of selfing and bottlenecks on genetic polymorphism using microsatellite markers in 14 natural populations (under a hierarchical sampling design) of the hermaphrodite freshwater snail Bulinus truncatus. These population genetics data allowed us to discuss the currently available mutation models for microsatellite sequences. Microsatellite markers revealed an unexpectedly high levels of genetic variation with < or = 41 alleles for one locus and gene diversity of 0.20-0.75 among populations. The values of any estimator of Fis indicate high selfing rates in all populations. Linkage disequilibria observed at all loci for some populations may also indicate high levels of inbreeding. The large extent of genetic differentiation measured by Fst, Rst or by a test for homogeneity between genic distributions is explained by both selfing and bottlenecks. Despite a limited gene flow, migration events could be detected when comparing different populations within ponds.

[Arguments for the modification of the genome (introgression) of the human parasite Schistosoma haematobium by genes from S. bovis, in Niger]. / Arguments en faveur d'une modification du génome (introgression) du parasite humain Schistosoma haematobium par des gènes de S. bovis, au Niger.

Characterization of schistosome populations from human in eastern Niger, through intra-uterine egg morphology of female parasites and phenotopic analyses of worms observed for acid phosphatase using electrophoretic separation, renders results that suggest an intogression of S. haematobium from man by genes of S. bovis, a parasite of domestic livestock. The origin of this introgression, that could implicate S. curassoni as well, another livestock parasite that hybridize with S. bovis, is discussed.