Vector control as a pathway to eliminate malaria in Africa
Vector control, to a greater extent than drugs or vaccines, has been responsible for shrinking the global map of many vector-borne diseases (VBDs), yet not as much emphasis or funding is allocated to it in various interventions in Africa. Vector control has played a principal role in the control of malaria, particularly in endemic areas such as sub-Saharan Africa. However, effective control of malaria vectors and ultimately, the elimination of malaria is still a major global challenge.
Despite steady advances in reducing the global burden of malaria, disruptions to health services caused by Covid-19 in 2020, resulted in a 12 percent rise in malaria deaths compared to the previous year. Following the longstanding pattern, the vast majority of all malaria cases (95%) and malaria deaths (96%) were in the African Region, with about 80 percent of all malaria deaths in the region among children under the age of 5.
In October 2021, the World Health Organisation (WHO) recommended the RTS, S/AS01 malaria vaccine for children aged six months to five years, living in moderate- to high-transmission settings, however, vaccine supplies are currently limited. African governments must therefore emphasize the control of malaria mosquito vectors according to strategies of integrated vector management (IVM).
Shifting our focus to integrated and locally adapted vector control and augmenting current vector control interventions is crucial to achieving the Global Technical Strategy for Malaria 2016–2030 target of reducing global malaria incidence and mortality rates by at least 90 percent by 2030.
Given the non-negotiable role of vector control in eliminating malaria in Africa, national policies must now be realigned to mobilise the political and financial support necessary to exploit these opportunities
Current malaria vector control interventions and challenges
In Africa, the core vector control measures deployed by national malaria programmes (NMPs) are long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS). LLINs and IRS reduce the risk of malaria infection by targeting indoor biting mosquitoes. High coverage and utilisation of LLINs and IRS is recommended for malaria endemic countries. However, while these two interventions are effective in malaria control, they are not sufficient to eliminate malaria.
The major challenges with LLINs and IRS are insecticide resistance, misuse of the interventions, host behaviour, such as staying outdoors during early night or sleeping outdoors without using protective measures, and vector behaviour including feeding on bovine blood, outdoor biting and outdoor resting. Hence, the scale-up of LLINs and IRS can cause a substantial decline in malaria burden, but fail to completely interrupt malaria transmission.
To achieve malaria elimination, there is a need to use a combination of vector control tools that target malaria vectors at different life cycle stages besides LLINs and IRS, thus preventing outdoor and indoor malaria transmission.
Strategies to strengthen malaria vector control in Africa
Several substantive opportunities now exist for rapidly developing and implementing more diverse, effective and sustainable malaria vector control strategies for low and middle-income countries (LMICs). A diverse range of emerging or repurposed technologies are becoming available for targeting mosquitoes when they enter houses, feed outdoors, attack livestock, feed on sugar or aggregate into mating swarms.
For example, mosquito control in high-income countries is predominantly achieved with a combination of mosquito-proofed housing and environmental management, supplemented with large-scale insecticide applications to larval habitats and outdoor spaces that kill off vector populations en masse, but all these interventions remain under-used in LMICs.
In view of these, Bloom Public Health recommends the following strategies to strengthen malaria vector control in Africa:
• Improving housing conditions: Mosquito-proof housing is a viable supplementary method to LLINs or IRS in malaria elimination strategies. Research shows that windows and doors screened with wire-mesh can significantly reduce indoor vector density, entomological inoculation rate and malaria incidence. In Africa, this strategy can be implemented using locally available materials. It is affordable, locally acceptable and also durable.
• Odour-baited mosquito trapping systems: A synthetic odour blend comprising mosquito attractants can be used as a means to trap and kill mosquitoes. Studies show that odour-baited stations can reduce malaria vector density and can supplement LLINs as a potential option to reduce outdoor biting. Odour-baited traps are an affordable tool to help the malaria elimination plan in Africa.
• Chemical larvicide spraying: Common larvicidal chemicals such as Temephos (Abate®) are effective and potential complementary tools to control malaria in areas with breeding sites, such as urban areas, dams, irrigation canals and other developmental areas. Another effective chemical larvicide is Bacillus thuringiensis H-14, a bacteria larvicidal based on insecticidal crystal proteins that are specifically toxic to mosquitoes. However, the chemical and spray equipment are expensive.
• Effective monitoring for establishment of data-driven vector control approaches: Malaria vector control requires periodic collection and interpretation of data on local vector species, the potential invasion by vectors from other geographical areas, their susceptibility to insecticides and vector and human behaviours. Ongoing monitoring of the coverage, usage, quality and durability of vector-control interventions is also vital. Also, programmatic development and evaluation of decentralised, locally managed systems for delivering proactive malaria vector control in Africa would enable broader scale-up.
Given the non-negotiable role of vector control in eliminating malaria in Africa, national policies must now be realigned to mobilise the political and financial support necessary to exploit these opportunities, so that national malaria control and elimination programmes can access a much broader, more effective set of vector control interventions.