Biology of two larval morphological phenotypes of Aedes aegypti in Abidjan, Côte d'Ivoire.

Since 2008, several outbreaks of yellow fever and dengue occurred in Abidjan, the economic capital of Côte d'Ivoire. A better knowledge of the biology of Aedes aegypti populations, the main vector of yellow fever and dengue viruses, is necessary to tailor vector control strategies implemented in the city. This study was designed to determine some biological parameters, occurring during the life cycle of two morphological phenotypes of Ae. aegypti larvae. Mosquitoes were sampled in a suburb of Abidjan (Treichville) using the WHO layer-traps technique. Biological parameters were studied in laboratory under standard conditions of temperature (27°C ± 2°C) and relative humidity (80% ± 10%). Our results indicated that the mean eggs laid by females from 'brown larvae' (BL) (85.95, 95% confidence interval (CI 95%) 78.87-93.02) was higher than those from 'white larvae' (WL) (64.40%, CI 95% 55.27-73.54). The gonotrophic cycle was 3 and 4 days in females from BL and WL, respectively. The overall yield of breeding mosquitoes from BL (63.88%, CI 95% 62.61-65.14) was higher compared with those of mosquitoes from WL (59.73%, CI 95% 58.35-61.12). The sex ratio (male/female) was 0.95 and 1.68 in Ae. aegypti populations from BL and WL, respectively. Females from BL lived slightly longer than those from WL (t = -2.332; P = 0.021). This study shows that Ae. Aegypti populations from BL and WL present different biological parameters during their life cycle. This could have an implication on their ability to transmit human disease viruses such as dengue and yellow fever. Further molecular studies are needed to determine genetic divergence between these Ae. aegypti populations.

[Culex quinquefasciatus sensitivity to insecticides in relation to the urbanization level and sewage water in Yopougon, a township of Abidjan (Côte-d'Ivoire)]. / Sensibilité de Culex quinquefasciatus aux pyréthrinoïdes en relation avec le niveau d'urbanisation et l'évacuation des eaux usées dans la commune de Yopougon à Abidjan (Côte-d'Ivoire).

This survey, conducted from July 2003 to June 2004, was to assess the variation of the level of sensitivity of Cx. quinquefasciatus to the pyrethroids recommended for the impregnation of the mosquito nets, in the township of Yopougon situated in the Northwest of Abidjan city in relation with the bed of a drainage channel of sewage water that passes through the township from the north to the south. Five districts have been chosen along this channel according to the level of urbanization, for the withdrawal of the pre-imaginal populations of Cx. quinquefasciatus in collections of stagnant sewage water of this township. The female Cx. quinquefasciatus aged three to five days from the exits of the insectarium have been exposed to papers impregnated with deltamethrin 0.05%, permethrin 1% and DDT 4% in view of the diagnosis of a possible resistance of these populations to these insecticides. The populations of Cx. quinquefasciatus proved to be resistant to the three insecticides used, in four districts. On the other hand, the population of Cx. quinquefasciatus from the district "Zone industrielle," situated upstream of the channel, proved to be sensitive to permethrin 1%, and a drastic decrease of sensitivity of the same mosquito has been observed with deltamethrin 0.05% and DDT 4%.

[Influence of the temperature on the development of the African cat flea Ctenocephalides felis strongylus (Jordan, 1925) (Siphonaptera : Pulicidae)]. / Influence de la température sur le développement de la puce africaine du chat Ctenocephalides felis strongylus (Jordan, 1925) (Siphonaptera : Pulicidae).

Ctenocephalides felis (Bouché, 1835) commonly called "cat's flea" presents two recognized subspecies: Ctenocephalides felis strongylus (Jordan, 1925), observed in the African continent, and Ctenocephalides felis felis (Bouché, 1835) in the other regions (North Africa, Europe and America) (Ménier and Beaucournu, 19991. In sub-Saharan Africa, the principal flea found in the pets and certain livestock (ovine, caprine and bovine), belongs to the subspecies C. f. strongylus. Some bio-ecologic parameters of C. f. strongylus were studied in various conditions of breeding and the results compared with those currently available for C. f. felis. At 75% +/- 5 of relative humidity, the development cycle of C. f. strongylus lasts 20-21 days at 27 degrees C and 16 to 17 days at 29 degrees C. In comparison with C. f. felis, it is shown that for identical breeding temperatures, the African subspecies of the cat flea develops itself slowly. This difference could be explained by the influence of the climate of their respective areas of distribution on their development cycle. With 75% +/- 5 of relative humidity, C. f. strongylus cannot survive more than 14 days in temperatures ranging between 27 and 29 degrees C, and this without any blood meal. Under the same conditions, this duration of survival does not exceed 16 days at 19 degrees C. But when C. f. strongylus has taken a first blood meal, its lifespan is much shorter when it is out of its host. Indeed, no individual is found living three days passed out of the fur of its host at 29 degrees C, five days at 27 degrees C and eight days at 19 degrees C. It is the same for C. f. felis. These data on bio-ecology of C. f. strongylus enable to understand the influence of temperature on its development cycle and consider more efficient strategies of control.

[Specific diversity and culicidian nuisance in the villages of N'gatty and Allaba in laguna area of Ivory Coast]. / Diversité spécifique et nuisance culicidienne dans les villages de N'gatty et d'Allaba en milieu côtier lagunaire de Côte-d'Ivoire.

Entomological surveys were undertaken between June and December 2006 in N'gatty and Allaba. These villages are located in southern Ivory Coast in a laguna area in Dabou department. In these villages, there are large swampy areas, which have caused the multiplication of anthropophilic Culicidae. Mosquitoes have been collected at preimaginal stage at the time of the larval prospecting and at adult stage through human landing catch. Larval collections have been made using the classic method of "dipping". Larvae have been identified to the genus level. Then, they have been bred in the laboratory to identify adults. Adults collection has been made once a month during three consecutive nights by human landing catch inside houses. Adults have been identified to the specific level. Eight genera of mosquitoes have been collected in these two villages: Aedes, Anopheles, Coquillettidia, Culex, Eretmapodites, Mansonia, Toxorhynchites and Uranotaenia. Twenty-four species have been listed during this stu y. The genus Mansonia is the most predominant with 86% (N = 15,811) and 80% (N = 1,385), respectively, in N'gatty and Allaba. The average biting rate per day varies between N'gatty and Allaba. It is estimated to 308 bites per human per night (b/h/n) in N'gatty and 72 b/h/n in Allaba. In these villages, mosquito nuisance is mainly due to Mansonia with 264 b/h/n and 58 b/h/n, respectively, in N'gatty and Allaba. However, Anopheles gambiae s.l. average rate was 12 b/h/n in N'gatty and 2 b/h/n in Allaba.

[Eco-distribution and Trypanosoma infection of Glossina palpalis palpalis in the Banco forest of and its relics, Abidjan (Côte d'Ivoire)]. / Chorologie et infection par les trypanosomes de Glossina palpalis palpalis dans la forêt du Banco et ses reliques, Abidjan (Côte d'Ivoire).

In order to implement an anti-vector programme in the suburb of Abidjan (Côte d'Ivoire), investigations were conducted to assess the tsetse fly densities as well as infection with trypanosomes. Catches were carried out during the rainy season and dry season with Vavoua traps laid during four consecutive days in different sites (Banco forest, Abidjan zoological park, area of the University of Abobo-Adjamé). One species of tsetse fly (Glossina polpalis palpalis) and two species of trypanosomes (Trypanosoma congolense, T. vivax) have been revealed. The apparent density per trap per day (DAP) is very high in the zoological park, 54.8 tsetse fly/trap/day during the dry season and 28.1 during the rainy season. At the University of Abobo-Adjamé, the DAP is respectively 13.5 and 8.1 tsetse fly/trap/day during the rainy season, and in the dry season it is only 0.9 and 0.8 in the Banco Forest. The physiological age on all sites is as follows: 57.5 % of old parous, 39% of young parous and 3.6 % of nulliparous in the rainy season. These proportions vary to 51.9% of young porous, 47.1% of old parous and 1% of nulliparous in the dry season. The overall infection rate is estimated at 20.7% in the rainy season and 20% in the dry season. Statistical analysis have showed a significant difference in the distribution of infection rates.

[Vectorial transmission of malaria in shrubby Savannah area at Ganse, Ivory Coast]. / Transmission vectorielle du paludisme en savane arborée a Ganse en Côte d'Ivoire.

A longitudinal entomologic study was carried out in the village of Ganse located in the Northeastern Ivory Coast from July 2000 to July 2001. The threefold purpose of the study was to index Plasmodium-carrying Anopheles species by capturing mosquitoes on human volunteers, collecting larvae in different dwelling types, and evaluating the involvement each species in the malaria transmission. A total of 4 species belonging to the Anopheles genus were collected in the village. Identification of circumsporozoite protein using the ELISA technique demonstrated that three species were plasmodium vectors. These species belonged to the An. gambiae complex (An. gambiae s.s. 100%), to the An. funestus group (An. funestus s.s. 95.6%) and to the An. nill group (An. nili s.s. 100%). The estimated mean sporozoite index was 5.9% for An. gambiae s.l., 4.3% for the An. funestus group and 2.6% for the An. nili group. The main larva breeding sites were standing water such as puddles for An. gambiae s.l., streams with tall plants for the An. funestus group and the Comoe River for An. nili group. Because peak breeding of these three species occurs at three successive times; i.e., in May, September and July respectively, transmission of P. falciparum is continuous throughout the year. The transmission rate is high since we recorded up to up to 410 infected bites per person per year. In addition to showing the presence of An. rivulorum-like, our findings in the area demonstrates the important role of An. nili s.s. in the transmission and the complexity of the vectorial system.

[The impact of urbanization on malaria infection rate and parasite density in children in the municipality of Yopougon, Abidjan (Côte d'Ivoire)]. / Impact de l'urbanisation sur l'indice plasmodique et les densités parasitaires chez les enfants de 0 à 5 ans dans la commune de Yopougon, Abidjan (Côte d'Ivoire).

From September 23-30, 2005, we conducted a cross-sectional study in six townships of Yopougon, a municipality of Abidjan. These townships were grouped in three levels of urbanization (village, precarious township, and residential township). The main objective of this survey was to determine the impact of urbanization on the malaria infection (parasite) rate and parasite density, and their consequences on the heterogeneity of malaria transmission in urban Abidjan. Specifically we compared these rates in all three urbanization levels, selecting two townships for each level to take environmental specificities observed from previous data into account. The study included 400 households per township. All children younger than 5 years in these households were included. Thick and thin blood smears were taken for each child on slides, and each slide was examined by microscope after staining. The malaria infection rate was 21.8%, indicating mesoendemic malaria. Its distribution varied significantly between the three urbanization levels. Malaria parasite densities also varied significantly between them. These results confirm the involvement of urbanization in the heterogeneity of malaria transmission in the city of Abidjan.

[Detection of the IS2404 insertion sequence and ketoreductase produced by Mycobacterium ulcerans in the aquatic Heteroptera in the health districts of Dabou and Tiassalé in Côte d'Ivoire]. / Mise en évidence de la séquence d'insertion IS2404 et de la kétoréductase (Kr) produite par Mycobacterium ulcerans chez les Hétéroptères aquatiques dans les districts sanitaires de Dabou et Tiassalé en Côte d'Ivoire.

Buruli ulcer (BU) disease, caused by Mycobacterium ulcerans, is a major public health problem in Côte d'Ivoire. Until now, the mode of BU transmission was unknown, but recent studies implicate aquatic Heteroptera in the chain of transmission. This study was launched in Côte d'Ivoire to search for specific genetic markers for M. ulcerans in these bugs, including the insertion sequence IS2404 and ketoreductase (Kr), both involved in the synthesis of mycolactone, a toxin produced by these mycobacteria. Samples of aquatic Heteroptera were collected monthly with deep nets from ponds near villages in the health districts of Dabou and Tiassalé. After identification and enumeration of the bugs, batches of the same taxon underwent real-time PCR to search for the IS2404 target and Kr. Saliva of 69 specimens of Diplonychus sp randomly selected in the samples was also analyzed by PCR. In all, 283 single-taxon batches were created. Thus, PCR identified 26 batches belonging to the families of Belostomatidae, Naucoridae, Corixidae, Ranatridae, and Nepidae as positive for both targets. The IS2404 insertion sequence and Kr were present in 6 of the 69 samples analyzed in the saliva of Diplonychus sp. These aquatic Heteroptera suspected of infection by M. ulcerans might release it into the environment because of their ability to fly. They might thus be the source of human contamination.

[Screening for urinary schistosoma by strips reactive to hematuria. Evaluation in zones of intermediate and weak endemicity in the Ivory Coast]. / Dépistage de la schistosomose urinaire par bandelettes réactives a l'hématurie. Evaluation en zones de moyenne et faible endémie de Cote-d'Ivoire.

Sticks Hemastix, reactive to haematuria have been tested into a focus ivory coast located in a humid savanna area. Into this focus the prevalence rate of urinary schistosomiasis (Schistosoma haematobium) was 27% taken as a whole and 40% for 5 to 19 years old persons. This study has shown that reactive sticks have a good sensitivity and an acceptable specificity compared with filtration. More, a good correlation between intensity of eggs count and the haematuria is observed.