Seasonal Dynamics of Symptomatic and Asymptomatic Plasmodium falciparum and Plasmodium vivax Infections in Coendemic Low-Transmission Settings, South Ethiopia.

Ethiopia has a plan to eliminate malaria in selected low-transmission districts by 2025. However, complex factors such as seasonality, focal heterogeneity, and coendemicity of Plasmodium vivax and Plasmodium falciparum, and asymptomatic cases, along with other factors, pose challenges. This longitudinal study assessed these dynamics and associated factors in three elimination-targeted settings in southern Ethiopia. The study included rural districts (Wonago and Yirgacheffe) and an urban setting (Dilla town) with 504 participants from 168 households per season. The study covered the peak and minor malaria transmission seasons and the dry season. Finger-prick blood was collected for microscopy, rapid diagnostic tests, and 18S-rRNA-based quantitative polymerase chain reaction (qPCR). During the dry season, P. vivax accounted for most infections (64.5%, 71/110) and symptomatic malaria (50.9%, 29/57), whereas P. falciparum dominated during the peak transmission season (45.7%, 42/92 infections and 58.1%, 25/43 of symptomatic cases). Treatment-seeking behavior was low, with 65.3% (143/219) of symptomatic individuals not seeking treatment. Dilla town had significantly higher infection prevalence (29.6%, 149/504, P <0.001) in all seasons compared with the rural sites. The incidence rate was 12/1,000 person-seasons by qPCR and 5/1,000 person-seasons by microscopy. Urban residents, those with low hemoglobin levels, nonuse of mosquito nets, and proximity to stagnant water had a significantly higher risk of infection (P <0.001). Tailored approaches are needed in elimination-targeted areas, focusing on urban settings, Plasmodium species, and strengthening community-level interventions for behavioral change and active case detection.

Evidence for a role of Anopheles stephensi in the spread of drug- and diagnosis-resistant malaria in Africa.

Anopheles stephensi, an Asian malaria vector, continues to expand across Africa. The vector is now firmly established in urban settings in the Horn of Africa. Its presence in areas where malaria resurged suggested a possible role in causing malaria outbreaks. Here, using a prospective case-control design, we investigated the role of An. stephensi in transmission following a malaria outbreak in Dire Dawa, Ethiopia in April-July 2022. Screening contacts of patients with malaria and febrile controls revealed spatial clustering of Plasmodium falciparum infections around patients with malaria in strong association with the presence of An. stephensi in the household vicinity. Plasmodium sporozoites were detected in these mosquitoes. This outbreak involved clonal propagation of parasites with molecular signatures of artemisinin and diagnostic resistance. To our knowledge, this study provides the strongest evidence so far for a role of An. stephensi in driving an urban malaria outbreak in Africa, highlighting the major public health threat posed by this fast-spreading mosquito.