Urban malaria in Accra, Ghana: transmission risk and influence of irrigated vegetable farms

Abstract

Urban malaria transmission in sub-Saharan Africa is often underestimated, emphasizing the need for research on vector distribution, abundance, behavior, and infectivity in cities. Urban malaria transmission has been on the rise across sub-Saharan Africa since 2003. Also, 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. 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 malaria vectors were assessed. Molecular methods were used to detect sporozoite infection, bloodmeal sources, vector species, and insecticide resistant mutation genes. 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%, 589/1,884), Culex (57.21%, 1,078/1,884), and Aedes (11.52%, 217/1,884). Overall, the IUF site category had the highest abundance of An. gambiae s.l. (48.63%, 10,466/21,520), followed by the PU (18.06%, 3,887/21,520), HS (16.42%, 3,533/21,520), MS (13.74%, 2,956/21,520) and LS (3.15%, 678/21,520) in both HLC and Procopack collections. Indoor An. gambiae s.l. had higher sporozoite infectivity (4.56%, 16/351) than outdoor (3.78%, 9/238) (χ² = 6.78, P = 0.009). Tuba, an urban irrigated site, had the highest sporozoite infectivity (6.41%, 10/156), with higher indoor (6.82%, 6/88) than outdoor (5.88%, 4/68) rate. This study showed that irrigated urban Agriculture drives urban malaria transmission in Accra, with high human bloodmeal indices and sporozoite infectivity, especially indoors. Targeted indoor control and management of immature vector habitats in IUF areas is essential to reduce transmission.