By Anya Fedorova, Country Representative, PSI Angola; Catia Marques, Entomology manager, PSI Angola
In tropical Angola, with some regions prone to eight-month-long rainy seasons, malaria is an endemic disease and top public health concern. Until now, the main malaria vectors consisted of mosquitoes that primarily bite indoors and during nighttime, with a higher incidence during the rainy season – although transmission occurs throughout the year. The recent establishment and expansion of the invasive vector Anopheles stephensi could drastically change the risk landscape.
Historically found in urban and peri-urban areas in Southeast Asia and parts of the Arabian Peninsula, An. stephensi is a type of mosquito capable of transmitting the two most common and deadly malaria parasites: Plasmodium falciparum and Plasmodium vivax. Global trade and travel have facilitated the spread of these disease-carrying mosquitoes, which were detected on the African continent for the first time in Djibouti in 2012. Since then, An. stephensi has been confirmed in six other African countries including Sudan, Ethiopia, Somalia, Kenya, Nigeria, and Ghana.
Recognizing the grave threat An. stephensi poses to Angola, the Ministry of Health and the National Malaria Control Program are embarking on an effort to monitor for the presence of this invasive mosquito species. The initiative receives support from the U.S. President’s Malaria Initiative (PMI) under the Health for All (HFA) project, led by Population Services International and our partner, the Mentor Initiative.
The success of this invasive species lies in its ability to exploit human transportation routes and thrive in urban environments. Most mosquitoes capable of transmitting malaria thrive in natural habitats, such as agricultural irrigation, ground pits left by construction or bricking, and the edges of streams and receding water sources. An. stephensi, however, thrives in man-made containers that are increasingly available in urban and peri-urban areas, including tires, cisterns, storage jars, and gutters. This makes them particularly effective at breeding and developing in areas where typical African Anopheles mosquitoes were less effective. Unlike many of its more common counterparts in the region, An. stephensi is an indoor and outdoor biter at all times of the day, which can reduce the effectiveness of indoor residual spraying and the mosquito net – two of the most important prevention means in the malaria toolbox. An. stephensi has also shown resistance to elevated temperatures and several types of insecticides. This combination of characteristics can lead to more malaria cases, overwhelm the healthcare system, and hinder the effectiveness of vector control measures that are key in fight against malaria in Africa.
Monitoring the invasive mosquitoes is the first step at effectively responding to the threat posed by An. stephensi. The global malaria community has highlighted one key area of intervention to detect and respond to An. stephensi: the critical need for collaboration with sectors normally not as engaged in the malaria response. In response to this call to action, the Angolan Ministry of Health has set out to cultivate strategic collaborations with the Ministry of Transport and the Port of Luanda to set up surveillance activities in areas most likely to be invaded by An. stephensi: in the ports and in neighboring communities. The An. stephensi monitoring activities will commence in September 2023, involving interdisciplinary teams from both ministries and HFA project entomologists. Subsequently, the project will extend to the Port of Soyo, located at the mouth of the Congo River in the province of Zaire.
The HFA project proudly supports Angola’s proactive and collaborative approach and is actively engaging with the private sector to bolster the Ministry of Health’s entomological monitoring efforts in other potential points of entry for this invasive mosquito species. Rapidly detecting and responding to An. stephensi will be critical to ensure the appropriate response measures are taken to minimize the risk this malaria vector can pose to communities across the country.