Larval ecology and infestation indices of two major arbovirus vectors, Aedes aegypti and Aedes albopictus (Diptera: Culicidae), in Brazzaville, the capital city of the Republic of the Congo

Abstract

Background: Invasive mosquito species, such as Aedes albopictus in Congo can affect the distribution of native species, changing the vector composition and pattern of disease transmission. Here, we comparatively establish the geographical distribution and larval habitat preference of Ae. aegypti and Ae. albopictus and the risk of arbovirus disease outbreaks using Stegomyia indices in the city of Brazzaville, the capital of the Republic of the Congo.

Methods: Human dwelling surveys of water-holding containers for immature stages of Aedes was carried out in December 2017 in Brazzaville through a random cluster sampling method. A total of 268 human dwellings distributed in 9 boroughs and 27 neighbourhoods were surveyed across the city.

Results: Overall, 455 potential larval habitats were surveyed. Both Ae. aegypti and Ae. albopictus were collected across the city with an overall high prevalence of Ae. aegypti (53.1%) compared to Ae. albopictus (46.9%). Geographical distribution analysis showed that Ae. aegypti was more abundant (mean = 6.6 ± 1.4) in neighbourhoods located in downtown, while the abundance of Ae. albopictus was low (mean = 3.5 ± 0.6) in suburbs. Peridomestic containers, especially discarded tanks, were the most strongly colonized productive larval habitat for both mosquito species with the prevalence of 56.4% and 53.1% for Ae. aegypti and Ae. albopictus, respectively. Globally, the house index (HI), Breteau index (BI) and container index (CI) were high for Ae. aegypti (26.6%, 38.4% and 22.6%) and Ae. albopictus (33.3%, 49.6% and 26.6%) compared to the transmission risk threshold (5%, 5% and 20%) established by the WHO/PAHO. Overall, pupae-based indices (the pupae index and the pupae per person index) were not significantly different between Ae. aegypti (273.4% and 23.2%) and Ae. albopictus (228.8% and 19.5%).

Conclusions: The findings of this study suggest a high risk for transmission of arbovirus diseases in Brazzaville and call for an urgent need to implement vector control strategies against these vectors in the Republic of the Congo.

Keywords: Aedes aegypti; Aedes albopictus; Larval ecology; Republic of the Congo; Transmission risk.

Fig. 1

Map of Brazzaville indicating mosquito sampling sites

Fig. 2

Total abundance of pupae and of immature stages of Aedes aegypti (a, b) and Ae. albopictus (c, d) per container type. Abbreviations: DT, discarded tanks; FP, flower-pots; M, miscellaneous; ST, storage tanks; and UT, used tires. Each dot represents the log₁₀-transform of the abundance of containers infested by immature stages of Ae. albopictus and Ae. aegypti

Fig. 3

Geographical distribution of Ae. aegypti and Ae. albopictus in Brazzaville boroughs in 2017. a Spatial distribution and abundance of Ae. aegypti and Ae. albopictus according to the neighbourhoods. b Spatial distribution of positive larval habitats, and their occupancy (Ae. aegypti only; Ae. albopictus only; both Ae. aegypti; and Ae. albopictus) according to the neighbourhoods

Fig. 4

Level of infestation of Ae. aegypti and Ae. albopictus in Brazzaville in 2017. a Overall Stegomyia and pupae indices of Ae. aegypti and Ae. albopictus in Brazzaville. b Infestation indices of Ae. aegypti and Ae. albopictus according to the location of the borough. Abbreviations: BI, Breteau index (and 95% confidence interval); CI, container index (and 95% confidence interval); HI, house index (and 95% confidence interval); PI, pupae index (and 95% confidence interval); PPI, pupae per person index (and 95% confidence interval)

Fig. 5

Infestation indices of Aedes spp. according to each borough. a BI, Breteau index (and 95% confidence interval). b HI, house index (and 95% confidence interval); black and red dashed line, represent the yellow fever and dengue epidemic threshold, respectively, defined by the WHO and PAHO

Fig. 6

Pupae based indices of Ae. aegypti and Ae. albopictus according to each borough. a PI, pupae index (and 95% confidence interval). b PPI, pupae per person index (and 95% confidence interval)