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.

[Entomological evaluation of the risk of urban outbreak of yellow fever in 2008 in Abidjan, Côte d'Ivoire]. / Évaluation entomologique du risque d'épidémie urbaine de fièvre jaune survenue en 2008 dans le district d'Abidjan, Côte d'Ivoire.

In April 2008, seven years after the outbreak of 2001, Abidjan faced another epidemic of yellow fever. Three weeks after the case detected in the commune of Treichville at 28(th) of April 2008, two other cases were notified, the first one in Port-Bouet and the second one in Cocody located respectively in the south and north of the city of Abidjan. In order to determine a large-scale risk of urban yellow fever epidemic, epidemiological and entomological investigations were conducted by the Ministry of Health and Public Hygiene of Cote d'Ivoire with the support of the Global Outbreak Alert and Response Network. Entomological investigations revealed the predominance of Aedes ægypti, urban vector of yellow fever in neighborhood visited with larval density indices between 2 and 5, indicating the existence of a sufficient density of the vector for cause an explosion of the epidemic. In fact, the massive influx of people from inside cities towards Abidjan caused by the socio-political crisis occurred in the country in 2002, the deterioration of environment with the creation of more breeding sites of Ae. ægypti as corollary and the circulation of the virus at mosquito level were many factors favorable to the yellow fever outbreak in Abidjan city.

[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%.

[Resistance of Anopheles gambiae s.l. to pyrethroids and DDT at Tiassalékro, an irrigated rice-growing village in the southern forest of Ivory Coast]. / Résistance d'Anopheles gambiae s.l. aux pyréthrinoïdes et au DDT à Tiassalékro, village de riziculture irriguée en zone sud forestière de Côte-d'Ivoire.

An assessment of the sensitivity of Anopheles gambiae s.l.to three pyrethroids (alphacypermethrin, permethrin, deltamethrin) and DDT has been carried out with a laboratory strain (Kisumu reference sensitive strain) and a wild strain (Tiassalékro strain) using larvae from an irrigated rice-growing area of Tiassalékro, located in the southern forest of Ivory Coast. The sensitivity tests were performed according to the standard WHO cylinder tests with adult female A. gambiae s.l. aged 2 to 4 days. The results showed that the strain of Tiassalékro is resistant to the three tested pyrethroids and DDT. The molecular forms M and S were identified, with a predominance of M form. The resistance mechanism involved is the Kdr mutation. In this region, control measures against malaria vectors by using bed nets impregnated with these insecticides or household sprays could be compromised.

[Micronecta sp (Corixidae) and Diplonychus sp (Belostomatidae), two aquatic Hemiptera hosts and/or potential vectors of Mycobacterium ulcerans (pathogenic agent of Buruli ulcer) in Cote d'Ivoire]. / Micronecta sp (Corixidae) et Diplonychus sp (Belostomatidae), deux hémiptères aquatiques hôtes et/ou vecteurs potentiels de Mycobacterium ulcerans agent pathogène de l'ulcère de Buruli en Côte d'Lvoire.

Buruli ulcer is currently a major public health problem in Côte d'Ivoire. It is a neglected tropical disease closely associated with aquatic environments. Aquatic insects of the Hemiptera order have been implicated in human transmission of Mycobacterium ulcerans, the pathogenic agent of Buruli ulcer. The purpose of this preliminary study using the polymerase chain reaction (PCR) method was to evaluate aquatic insects in Sokrogbo, a village in the Tiassalé sanitary district where Buruli ulcer is endemic. Findings identified two water bugs hosting Mycobacterium ulcerans, i.e., one of the Micronecta genus in the Corixidae family and another of the Diplonychus genus in the Belostomatidae family. The PCR technique used revealed the molecular signatures of M. ulcerans in tissue from these two insects. Based on these findings, these two water bugs can be considered as potential hosts and/or vectors of M. ulcerans in the study zone. Unlike Diplonychus sp., this is the first report to describe Micronecta sp as a host of M. ulcerans. Further investigation will be needed to assess the role of these two water bugs in human transmission of M. ulcerans in Côte d'Ivoire.

[Entomological investigations conducted around ten cases of yellow fever in 2009 in the Denguélé sanitary region, Côte-d'Ivoire]. / Investigations entomologiques menées autour de dix cas de fièvre jaune survenus en 2009 dans la région sanitaire du Denguélé, Côte-d'Ivoire.

In November 2009, ten suspicious cases of yellow fever, including six deaths, were notified in the region of Denguélé, in the northwest of Côte-d'Ivoire. In order to evaluate the extent of yellow fever virus circulation and the risk for local people, a mission of entomological investigation was carried out by the Ministry of Health and Public Hygiene of Côte-d'Ivoire. Entomological investigations were conducted in the villages of confirmed cases (Banakoro and Tron-Touba) and the centers of consultation and hospitalization of cases during illness. Breteau index and recipient index were quasi nil. Aedes aegypti was absent among the captured mosquitoes. On the other hand, Aedes luteocephalus and Aedes opok were present at Banakoro and Tron-Touba with respective average biting rates of 0.8 and 0.6 bite/man/twilight. This situation of epidemic in the northwest of Côte-d'Ivoire could be explained by the deterioration of Denguélé region's health system which is a consequence of the war started in the country in 2002 and which has lowered the immunity of the population.

[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.

[Entomological investigation following the re-emergence of yellow fever in 2008 in Abidjan area (Côte d'Ivoire)]. / Investigation entomologique à la suite de la réémergence de la fièvre jaune en 2008 à Abidjan (Côte d'Ivoire).

In April 2008, Abidjan was again faced with another case of yellow fever after the epidemic of 2001 causing mass immunization campaign. In order to evaluate the extent of amaril virus circulation and the risk for local people, an entomological investigation was carried out by the Ministry of Health and Public Hygiene of Côte d'Ivoire. At "Entent" area of Treichville, Breteau index was estimated at 34, recipient index at 20% and house index at 25%. Those indexes were respectively 53, 21 and 31% at "Vridi canal" of Port Bouet. In the both neighborhood, Aedes aegypti accounted for more than 80% of mosquitoes caught and more than 90% of mosquitoes adults obtained from larval breeding. This new situation of epidemic risk could be explained by several factors including the reception of 70% of forced migration people caused by the crisis in the country occurred in 2002, the probable drop of preventive immunization, the environment deterioration creating of more breeding sites of Ae. aegypti.

[Malaria transmission in Tiassalékro, a irrigated rice growing village situated in the South forest area of Côte d'Ivoire]. / Transmission du paludisme a Tiassalèkro, village de riziculture irriguèe situé en zone sud forestière de Côte d'Ivoire.

A longitudinal entomological study was carried out from January to June 2007 in the rice-growing area of Tiassaékro, a village located in the forest, South of Côte d'Ivoire. The study was based on samples of mosquitoes caught on human volunteers indoors and outdoors. During the 6 months of the study 29481 female mosquitoes were caught. The average biting rate was 272.9 bites per man per night (b/m/n). An. gambiae was the most predominant with 79.1% of mosquitoes caught. The average biting rate of An. gambiae was of 216 b/m/n. The biting activity of this species was noticed between 8 p.m. and 6 a.m. The estimated average sporozoite index was 0.32% (n = 3423 dissected). The inoculation rate was 0.69 ib/m/n with the highest rate (1.99 ib//n) recorded in April. The entomological parameters of the transmission are influenced by the different stages of rice growing.

[Knowledge, attitudes and practices of populations towards mosquitoes in urban and rural area (Côte d'Ivoire--West Africa)]. / Connaissances, attitudes et pratiques des populations vis-à-vis des moustiques dans la zone urbaine et périurbaine de Bouaké et dans les villages de Kafiné et de Kabolo (Côte d'Ivoire--Afrique de l'Ouest).

Three surveys related to the knowledge, attitude and practices of populations towards mosquitoes were conducted in Côte d'Ivoire. The first survey was undertaken in June 1994 in the city of Bouaké and the other two respectively in January 1996 and in June 1999 in the village of Kafiné. The surveys have revealed that whatever the environment, nuisance due to mosquitoes constitutes a great concern for the population of the villages. The majority of people interviewed in urban (94%), peri-urban (68%) zones and in Kafiné (94%) associates mosquito with malaria against 18% only in Kabolo. Furthermore, these surveys have allowed the inventory of methods of controlling mosquito currently used by the communities in both urban and rural areas. Generally mosquito coils as well as insect sprays are currently used because of their cheapness and their availability on the local market. in Bouaké, insect sprays (97% to 99%) are used as much as mosquito coils (87% to 98%). However, in Kafiné and Kabolo, insect sprays are only used by respectively 76% and 69% and the mosquito coils by respectively 68% and 71%. In urban zones, the insect sprays are more common than mosquito coils. On the contrary mosquito coils are currently used in villages due to their low price (40 to 50 FCFA) and their constant availability on the local market. Furthermore, local plants characterized by a repulsive essence are known by 48% and 75% of people interviewed respectively in the urban and peri-urban area of the city of Bouak6, by 74 % of the population of Kafiné and 73% of people living in Kabolo. In the last village 57% of people who were interviewed do not use any means of orotection due to financial reason; only 14% use mosquito coils and 20% use local plants with a repulsive essence. Mosquito net is known by the majority of people interviewed (82 - 98%) as an excellent means of orotection against mosquito bites. However only 27%, 13%, 26% and 5% of people respectively living in the urban and peri-urban areas of Bouaké and in the villages of Kafiné and Kabolo own their mosquito net. Its cost is the main reason for not using it as mentionned by 25% of people interviewed in the urban neighborhood, by 48% in the peri-urban areas, respectively 46% and 89% in the villages of Kafiné and Kabolo. Although its effectiveness has been proved by the communities, mosquito net still remains less common. Its price is relatively high (3500 - 5000 FCFA). It is not constantly available on the local market. Other socio-cultural factors such as local beliefs and taboos hinder the use of mosquito nets by the communities.

[Resistance of Culex quinquefasciatus (Say, 1823) to deltamethrin and the use of impregnated mosquito nets in an urban area of Bouaké, Côte d'Ivoire]. / Résistance de Culex quinquefasciatus (Say, 1823) à la deltaméthrine et l'utilisation de la moustiquaire imprégnée en milieu urbain de Bouaké, Côte d'Ivoire.

The efficacy of pieces of nets treated with two formulations of deltamethrin (concentrated suspension at 1% and tablets at 25%) against two strains of Culex quinquefasciatus ("S-Lab", sensitive strain and "Bouaké", local strain) has been evaluated at the laboratory by experimental tunnels tests. The observed mortality of the sensitive strain has been 2-3 time more important than that of local strain. This observation seems to be linked to Culex quinquefasciatus of Bouaké pyrethrinoids-resistance. The excito-repellency effect of the two formulations has been lower for the local strain than for the sensitive strain. It has also been more important with the tablet at 25% than with concentrated suspension at 1%. The blood feeding rate has been more important for the local strain than for sensitive strain and it has been lower with the tablet at 25% than with the concentrated suspension at 1%.

Comparison of the effect of two excipients (karite nut butter and vaseline) on the efficacy of Cocos nucifera, Elaeis guineensis and Carapa procera oil-based repellents formulations against mosquitoes biting in Ivory Coast.

Repellents in the form of dermal pomades are recommended as a protection against awakening and bedtime mosquito bites. If synthesis repellents are available, they are nevertheless not common and the prices remain out of reach for the communities concerned. The people therefore have to resort more and more to traditional concoctions, some of which have been shown to be effective. After demonstrating that oil-based formulations (lotions, creams, pomades) of Cocos nucifera (coconut), Elaeis guineensis (oil palm) and Carapa procera (gobi) were effective against mosquitoes, it became necessary to study the impact of the two excipients used in their manufacture, on the effectiveness of the repellents. Experiments were carried with Anopheles gambiae and Aedes aegypti under lobaratory conditions and any other mosquitoes collected under field conditions in Ivory Coast. The laboratory results indicate that the average protection times obtained with formulations with karite nut butter as excipient (54.8 +/- 37.0 mn and 74.6 +/- 26.4 mn respectively on An. gambiae and Ae. aegypti) are higher than those recorded with vaseline as excipient (respectively 42.7 +/- 30.0 mn and 60.8 +/- 33.9 mn). On the other hand, under field conditions, the biting rate percentage reduction obtained with the products with karite nut butter and vaseline excipient were similar (respectively 29.8% and 35.9% for all mosquitoes collected and 45.7% and 47.4% against An. gambiae). Nevertheless, the use of karite nut butter on repellent products should be encouraged because its sale price is very lower (10 time less) than the vaseline's.