Larval habitat diversity, physicochemical characteristics and their effect on the larval density of malaria vectors in the city of Accra, Ghana

TL;DR

This study explores how urban habitats in Accra, Ghana, affect the breeding of malaria-carrying mosquitoes, finding high larval densities in polluted and agricultural areas.

Contribution

The study identifies urban irrigation and polluted habitats as key drivers of malaria vector breeding in Accra, with the first detection of An. stephensi in the region.

Findings

Drainage ditches were the most common habitats for Anopheles larvae, with high larval density in irrigated urban farming areas.

Polluted habitats showed higher ammonium levels and lower dissolved oxygen compared to unpolluted ones.

An. coluzzii was the predominant malaria vector, and invasive An. stephensi was detected for the first time in the study area.

Abstract

Malaria is more prevalent in rural areas than urban partly due to less availability of Anopheles breeding habitats of natural origin in urban settings. However, urban factors such as irrigated farming, open sewers, and discarded containers create mosquito breeding sites. This study investigates the diversity and distribution of mosquito larval habitats and the impact of physicochemical characteristics on the presence and density of Anopheles gambiae s.l. larvae in Accra, Ghana.

Larval surveys and collections were conducted at fifteen locations in Accra, during both the dry season (February to March) and the rainy season (June to July) of 2022, using the WHO standard dipping method. These sites were divided into five categories: Irrigated Urban Farming (IUF), Lower Socioeconomic Status (LS), Middle Socioeconomic Status (MS), High Socioeconomic Status (HS), and Peri-urban (PU) areas. Physicochemical parameters were measured, and species identification was performed using morphological and molecular methods.

A total of 727 potential mosquito habitats were identified, with 65.34% (475/727) positive for Anopheles larvae. Drainage ditches were the most common habitat type (48.21%; 229/475). The highest abundance of An. gambiae s.l. was found in IUF sites (27.24%; 6,244/22,919), especially during the rainy season (77.01%; 17,650/22,919; R2 = 3.46, P = 0.000). Polluted habitats, including household effluents, had higher ammonium levels (3.4 mg/L NH4-N) compared to unpolluted ones (1.3 mg/L NH4-N). Other distinguishing parameters included dissolved oxygen (34% vs 52.9%), conductivity (5106 μS/cm vs 2049 μS/cm), and total dissolved solids (3181 mg/L vs 1255 mg/L). The predominant malaria vector was An. coluzzii (54.4%; 368/677). Additionally, the presence of invasive An. stephensi was detected in this study.

Malaria vectors breed in diverse and often polluted urban habitats, with high larval densities in urban agricultural areas. The detection of the invasive An. stephensi highlights the need for continuous monitoring and vector control strategies in urban settings.

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