Expansion of Aedes africanus (Diptera: Culicidae), a sylvatic vector of arboviruses, into an urban environment of Abidjan, Côte d'Ivoire.

In 2008, an outbreak of yellow fever occurred in Abidjan. The entomological investigations confirm that Abidjan is at risk of yellow fever with a suspicion of the National Park of Banco (NPB) forest as a likely area of re-emergence. This study aims to assess the dispersion of sylvatic vectors of arboviruses from the NPB forest to the surrounding areas (Andokoi and Sagbé). The sampling was done in the rainy season using the WHO layer-traps technique. Among the six species of Aedes sampled, Aedes aegypti and Aedes africanus were the potential vectors of arboviruses. Both species were collected in Sagbé but only Ae. aegypti in Andokoi. Only Ae. aegypti were present 400 and 800 m from NPB forest, but at 200 m, it showed respective proportions of 75.5% and 87.5% in Sagbé and Andokoi. In the NPB forest, however, Ae. africanus has been the predominant species. The study showed the presence of Ae. aegypti in Andokoi and Sagbé. However, Ae. africanus was found in the NPB forest and in the 200 m radius in Sagbé. The establishment of an entomological surveillance program in all areas would therefore be essential for the prevention of arboviruses outbreaks in Abidjan.

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.