Published in PLOS One on 2026-08-14, this study is presented as an attributed evidence briefing. The excerpts below are the original researchers’ words, reproduced under their Creative Commons Attribution licence. Health Signal has selected the abstract and, where needed, opening background paragraphs; the complete methods, results, limitations and references remain in the linked paper.
Original authors: Gabriel Haddad, Osman Abdillahi Guedi, Nicolas Gomez, Sébastien Briolant
Source: PLOS One • DOI 10.1371/journal.pone.0355973
Read the complete primary study ↗ · Creative Commons Attribution licence
From the researchers
Abstract
Anopheles stephensi is an invasive malaria vector found in South Asia and the Middle East. It was first described in Djibouti in 2012. It has since been linked to an increase in malaria cases and its spread to several African countries in the region. Given that the three biological forms of An. stephensi – Type, Intermediate, and Mysorensis – have different vectorial capacities and habitats, it is essential to know which forms are present in urban areas in Africa and which are responsible for malaria transmission.
In April 2023, in the city of Djibouti, a total of 600 eggs of An. stephensi were collected from six sites and analyzed using a scanning electron microscope to identify the biological forms based on the number of ridges. Sequence polymorphism in the intron I region of the odor-binding protein 1 (Obp1) gene was also analyzed in 153 specimens of An. stephensi. The distribution of biological forms of An. stephensi across the six sites was also analyzed in light of the incidence rate of malaria in the corresponding areas.
At all sites, the number of ridges observed on the eggs corresponds with all three biological forms of An. stephensi living sympatrically in Djibouti. In peri-urban and urban areas, even in areas with high malaria incidence, the majority of eggs had ridge counts consistent with the Mysorensis form, which is described as being associated with rural areas and low vector capacity. In addition, there was no correlation between morphological analysis and molecular analysis of Obp1.
All biological forms of An. stephensi are present in the city of Djibouti, where their role in malaria transmission requires further study in order to improve malaria control policies. Furthermore, Obp1 is not a suitable molecular tool for distinguishing the three biological forms of An. stephensi.
Introduction
Despite decades of effort, malaria remains a major public health challenge in 83 countries around the world, with most deaths occurring in Africa. According to the World Malaria Report, there were 263 million cases of malaria and 597,000 malaria-related deaths worldwide in 2023 [1]. Historically, malaria was considered a disease that only affected rural areas. Due to ongoing immigration and development, cities now have large areas of urban agriculture and are experiencing uncontrolled urban sprawl with poor water management, which provides a breeding ground for Anopheles species [2], including Anopheles stephensi [3].
Until 2010, An. stephensi was mainly described as a malaria vector in South Asia and certain neighboring countries on the Gulf Peninsula [4]. In 2012, it was detected for the first time in Djibouti [5], a country located in the Horn of Africa where it is responsible for Plasmodium falciparum and P. vivax transmission in humans [6]. Since then, its presence and rapid spread have been reported in several African countries [7–11] and have been clearly linked to the spread of malaria in the region [12,13].
Reading this evidence
Use the full paper to check the study design, participant selection, comparator and outcome definitions before drawing a practical conclusion. An association does not by itself show cause and effect. A reported performance measure needs its denominator and uncertainty. A finding from a particular facility, sample or time period should retain that scope when it is discussed elsewhere.
This briefing makes the source accessible within the wider public health desk. It does not assess an individual patient or certify a product. When considering relevance to another health system, examine the original authors’ account of context and limitations, then seek local implementation evidence. The related reporting below provides other studies to read alongside this one; it is a topic connection, rather than a claim that their results are directly comparable.
© 2026 Gabriel Haddad, Osman Abdillahi Guedi, Nicolas Gomez, Sébastien Briolant. Excerpts reproduced under CC BY. Selection, formatting and contextual notes by Health Signal. The researchers are the authors of the source study, not members of Health Signal’s staff.
Explore connected evidence
- Evidence brief: Modelling the impact of larviciding as a supplementary malaria vector control intervention in rural south-eastern Tanzania: A district-level simulation study
- Evidence brief: Heterogeneity of malaria transmission in urban settings in Ethiopia: A seroprevalence and risk factor analysis
- Evidence brief: Seasonal variation in species composition, deltamethrin susceptibility, and kdr mutations in anopheles mosquitoes in Northwest Ethiopia
