Malaria transmission risk in the city of Accra, Ghana: vector behavior and distribution.

Abstract

Background: Urban malaria transmission in sub-Saharan Africa is often underestimated, emphasizing the need for research on vector distribution, abundance, behavior, and infectivity in cities. Since 2003, urban malaria transmission has intensified. Monitoring Anopheles populations is crucial for developing effective interventions. This study examined the biting and resting habits, distribution, abundance, and Plasmodium infection of malaria vectors in Accra. Methods: Adult malaria vectors were collected using human landing catch (HLC) and Prokopack aspiration (PPK) at ten sites in Accra, categorized into five groups: sites with Irrigated Urban Farming (IUF), Lower Socioeconomic Status (LS), Middle Socioeconomic Status (MS), High Socioeconomic Status (HS), and Peri-urban (PU) areas. Biting patterns and entomological transmission indices of An. gambiae s.l. were assessed, Molecular methods were used to detect sporozoite infection, bloodmeal sources, vector species, and insecticide resistant mutation genes. Results: A total of 41,747 mosquitoes were collected. Of these, 95.49% (39,863/41,747) were host-seeking collected through human landing catch (HLC), consisting of Anopheles (52.54%, 20,945/39,863), Culex (42.00%, 16,742/39,863), Aedes (3.74%, 1,491/39,863), and Mansonia (1.72%, 685/39,863). The remaining 4.51% (1,884/41,747) were resting mosquitoes collected using a Procopack aspirator, comprising Anopheles (31.26%, 589), Culex (57.21%, 1,078), and Aedes (11.52%, 217). Overall, the irrigated urban farming (IUF) site category recorded the highest abundance of An. gambiae s.l. (48.63%, 10,466/21,520), followed by the peri-urban (PU) site category (18.06%, 3,887/21,520), high socioeconomic (HS) site category (16.42%, 3,533/21,520), middle socioeconomic (MS) site category (13.74%, 2,956/21,520), and low socioeconomic (LS) site category (3.15%, 678/21,520) in both HLC and Procopack collections. Significantly higher mosquito biting activity was observed during the late evening (LE), the classical mosquito biting time, in both the rainy (71.45%, 11,337/15,865) and dry (72.21%, 3,658/5,066) seasons. Indoor An. gambiae s.l. had higher sporozoite infectivity (70.64%, 77/109) than outdoor mosquitoes (29.35%, 32/109) (χ² = 6.78, P = 0.009). Tuba from the IUF site had the highest sporozoite infectivity (32.11%, 35/109), with higher indoor (24.77%, 27/109) than outdoor (7.34%, 8/109) rates. Conclusion: Anopheles gambiae s.l. drives urban malaria transmission in Accra, with high human bloodmeal indices and sporozoite infectivity, especially indoors. Urban agriculture promotes vector proliferation. Targeted indoor control and management of breeding sites in IUF areas are essential to reduce transmission.