Confronting Anopheles stephensi, A Rapidly Emerging Threat

Anopheles stephensi: A malaria spreading mosquito species that thrives in urban spaces and is resistant to multiple insecticides.

On World Mosquito Day, as we commemorate the strides made in combatting mosquito-borne diseases, we must turn our attention to a concerning emerging threat - Anopheles stephensi. Historically recognized as an Asian malaria vector, this mosquito species has ventured far beyond its native regions in recent years, presenting major challenges to malaria control efforts. 

Anopheles stephensi at a Glance

An. stephensi is a mosquito species capable of transmitting both Plasmodium falciparum and P. vivax malaria parasites. It was traditionally confined to South-East Asia and the Arabian Peninsula. However, since its first detection in Djibouti in 2012, this predominantly urban vector has rapidly expanded its geographical scope. It has spread its wings to Ethiopia (2016), Sudan (2016), Sri Lanka (2017), Somalia (2019), Nigeria (2020), Yemen (2021), Kenya (2022), and most recently, Ghana (2022). Its remarkable adaptability to urban environments and resistance to various insecticides pose unique challenges to malaria control efforts.

Understanding the Urban Challenge

Unlike its rural-dwelling Anopheles counterparts, An. stephensi thrives in urban landscapes, intensifying the intricacies of malaria control. Additionally, it displays resistance to primary insecticide classes employed for vector control. With its ability to feed both indoors and outdoors on animal and human hosts, this mosquito exhibits a high degree of adaptability. Rapid urbanization, coupled with inadequate planning and waste management, provides fertile breeding grounds for An. stephensi larvae in man-made water tanks, water storage containers, wells, pools and in less typical sites such as ponds along rivers and flooded areas.

Factors Fueling the Spread of An. stephensi

The spread of An. stephensi into new territories can be attributed to several factors:

1. Globalization and Travel - Heightened global travel and trade inadvertently facilitate the transportation of An. stephensi larvae and adults, leading to its establishment in non-native areas.
2. Urbanization - The rapid urbanization of developing countries creates ideal breeding sites for this urban-adapted mosquito, amplifying the risk of its expansion.
3. Climate Change - Altered weather patterns due to climate change can impact mosquito species distribution, including An. stephensi, as warmer temperatures and changing rainfall patterns create new suitable habitats.
4. Inadequate Vector Surveillance - Regions with limited entomological surveillance and diagnostic capabilities face challenges in early detection and response to the presence of An. stephensi.

Malaria Resurgence

The invasion of An. stephensi in sub-Saharan Africa, where over 40% of the population resides in urban areas and malaria burden is highest, is deeply concerning. Reports indicate that An. stephensi has contributed to malaria resurgences in African cities. This trend jeopardizes the progress made in reducing malaria cases. Additionally, its detection in Sri Lanka raises fears of malaria reintroduction in a country declared malaria-free only a few years ago.

The WHO Initiative

Recognizing the gravity of the situation, the World Health Organization (WHO) launched a new initiative in September 2022, designed to halt the further spread of An. stephensi in the African region and explore elimination strategies in invaded areas. It involves:

1. Strengthening Surveillance: Enhanced vector surveillance, entomological surveys, spatial mapping, and insecticide resistance monitoring.
2. Integrated Vector Management (IVM): Implementing IVM strategies, combining control measures like bed nets, spraying, larval management, and community engagement.
3. Research and Innovation: Investing in understanding An. stephensi behavior for targeted interventions.
4. Cross-Sector Collaboration: Collaborating with health, environmental, and urban agencies and communities for holistic solutions.
5. Community Empowerment: Involving communities, raising awareness, and empowering individuals in vector control efforts.

Addressing the Knowledge Gap

As emphasized by the WHO initiative, research plays a pivotal role in tackling this emerging biological threat. Containing An. stephensi requires a comprehensive understanding of its spread and transmission patterns. Extensive research is imperative to investigate its behavior, dynamics, distribution, and resistance mechanisms in new contexts. 

To support these efforts, MESA undertook a landscape review, diligently mapping global projects dedicated to this invasive mosquito species. This initiative entailed extensive database searches, collaborations with esteemed malaria professionals, and snowballing from relevant articles. The result of this vital undertaking is a comprehensive overview of An. stephensi research efforts worldwide. It sheds light on existing gaps in research and funding, facilitating informed decision-making and prioritization of future endeavors. 

The result of this vital undertaking is a comprehensive overview of An. stephensi research efforts worldwide. It sheds light on existing gaps in research and funding, facilitating informed decision-making and prioritization of future endeavors.

To further empower malaria professionals, MESA compiled the Anopheles stephensi resource compilation, a valuable repository providing essential resources and tools. This compilation serves as a one-stop-shop, offering easy access to crucial information, valuable data, and expert findings.

This World Mosquito Day, we must acknowledge the urgency of confronting emerging threats like An. stephensi. As An. stephensi continues its relentless expansion, we must draw valuable lessons from countries already grappling with its invasion and strengthen surveillance and monitoring systems to detect and respond promptly to its presence. Collaboration among diverse stakeholders, to prioritise and conduct research concurrently with implementing measures and proactive strategies in an integrated manner, is essential for developing timely and effective solutions to combat the spread of this mosquito vector.

NOW is the time to act!