High Aedes spp. larval indices in Kinshasa, Democratic Republic of Congo

Abstract

Background: Dengue, yellow fever, chikungunya and Zika are among the most important emerging infectious vector-borne diseases worldwide. In the Democratic Republic of Congo (DRC), increases in cases of dengue and outbreaks of yellow fever and chikungunya have been reported since 2010. The main vectors of these arboviruses, Aedes aegypti and Aedes albopictus, have been reported in DRC, but there is a lack of detailed information on their presence and spread to guide disease control efforts.

Methods: In 2018, two cross-sectional surveys were conducted in Kinshasa province (DRC), one in the rainy (January/February) and one in the dry season (July). Four hundred houses were visited in each of the four selected communes (N'Djili, Mont Ngafula, Lingwala and Kalamu). Within the peri-domestic area of each household, searches were conducted for larval habitats, which were then surveyed for the presence of Aedes larvae and pupae. A subset of the immature specimens were reared to adults for morphological identification followed by DNA barcoding of the specimens to validate identifications.

Results: The most rural commune (Mont Ngafula) had the highest pupal index (number of Aedes spp. pupae per 100 inspected houses) at 246 (20) pupae/100 houses, and Breteau index (BI; number of containers positive for immature stages of Aedes spp. per 100 households) at 82.2 (19.5) positive containers/100 houses for the rainy (and dry) season, respectively. The BI was 21.5 (4.7), 36.7 (9.8) and 41.7 (7.5) in Kalamu, Lingwala and N'Djili in the rainy (and dry) season, respectively. The house index (number of houses positive for at least one container with immature stages of Aedes spp. per 100 inspected houses) was, on average, across all communes, 27.5% (7.6%); and the container index (number of containers positive for immature stages of Aedes spp. per 100 inspected containers) was 15.0% (10.0%) for the rainy (and dry) season, respectively. The vast majority of Aedes-positive containers were found outside the houses [adjusted odds ratio 27.4 (95% confidence interval 14.9-50.1)]. During the dry season, the most productive containers were the ones used for water storage, whereas in the rainy season rubbish and tires constituted key habitats. Both Ae. aegypti and Ae. albopictus were found. Anopheles larvae were found in different types of Aedes larval habitats, especially during the rainy season.

Conclusions: In both surveys and in all communes, the larval indices (BI) were higher than the arbovirus transmission threshold values established by the World Health Organization. Management strategies for controlling Aedes in Kinshasa need to target the key types of containers for Aedes larvae, which are mainly located in outdoor spaces, for larval habitat destruction or reduction.

Keywords: Aedes; Central Africa; Chikungunya; Democratic Republic of Congo; Kinshasa; Survey.

Fig. 1

Maps indicating the survey sites. The four survey communes (light grey) with sampling areas indicated by red dots, in Kinshasa, 2018

Fig. 2a–g

Photos of various types of larval habitat identified/investigated in the study area. a Water storage tanks or cisterns (> 15 l); b small water containers (< 15 l) used for daily kitchen and cleaning activities; c rubbish and discards; d natural tree and bamboo holes; e artificial containers that are used by households and cannot be destroyed (e.g. animal drinking pots); f used tires; g natural ground surface pools

Fig. 3

Productivity of the habitats for immature stages of Aedes spp., Kinshasa, 2018

Fig. 4

Geographical and seasonal differences of the most productive habitats for Aedes spp. larvae, Kinshasa, 2018

Fig. 5

Neighbor-joining tree including the six medically important Aedes species of the subgenus Stegomyia occurring in the Afrotropical region. The generated haplotypes of Aedes albopictus and Aedes aegypti specimens of the Democratic Republic of Congo are highlighted in grey

Fig. 6

Types of habitats where Anopheles spp. larvae were encountered in the Kinshasa survey sites, 2018 (n = 32 mixed larval habitats positive for Anopheles)

Fig. 7

Distribution of habitats positive for Anopheles spp. larvae in the four survey communes in the rainy and dry season, Kinshasa, 2018 (n = 32 mixed larval habitats positive for Anopheles)