Malaria is a historical disease and has affected us for many years. Many great people have succumbed to the disease with the likes of the great Alexander, David Livingston and so many others making the list. To date, malaria continues to claim lives of many people every day. The majority of the world malaria transmissions occur in Africa, due to the presence of the most highly efficient malaria vectors that feed on humans and rest inside the house or in proximity to houses.
Success of bed net use and indoor spraying with insecticides
For decades, these behaviours have been exploited using indoor residual spraying (IRS) and insecticide treated bednets (ITNs) that kill mosquitoes when they land on treated walls or try to bite humans sleeping under ITNs respectively.
ITNs provide a protective physical barrier and the insecticides provide protection by directly killing or repelling host seeking mosquitoes. IRS targets resting mosquitoes that get in contact with insecticides upon landing on treated surfaces. This results in the reduction in feeding frequency and mosquito survival which consequently reduces mosquito vectorial capacity. The wide use of mosquito nets and indoor spraying with insecticides for malaria control has significantly contributed to the global reduction of malaria transmission for many years.
Pyrethroid resistance and mosquito behavioural change: challenges to mosquito control
On the other hand, the increase in the use of pyrethroids, which are widely used in ITNs has resulted in development of pyrethroid resistance in malaria vectors, leading to reduced efficacy of both mosquito nets and indoor spraying. Additionally, the use of these tools has contributed to changes in the biting and resting behaviours of Anopheles mosquitoes in different areas worldwide. Mosquitoes that bite and rest indoors are now becoming more flexible in their behaviours. They feed, and rest outside the houses and sometimes bite people early in the evening before they become protected by nets, thus sustaining malaria transmission. This behavioural shift together with increased insecticide resistance have a serious impact on malaria control, contributing to residual malaria transmission and consequently, to failures in malaria elimination. The impact of residual malaria transmission have been reported in many research papers such as that of Killeen and colleagues and have even been demonstrated in locations with a good ITNs and IRS coverage, reducing the possibility that IRS and ITNs alone can achieve malaria elimination. Consequently, novel mosquito control tools that will complement the current tools are recommended by the world health organization.
Need for novel and innovative complementary control tools
There is no single tool that will eliminate malaria. Implementation of a combination of old and newly developed control tools will facilitate the progress towards malaria elimination.
Currently, researchers are doing their best to come up with better ways of curbing malaria transmission. An exciting example is the newly developed attractive toxic/target sugar baits (ATSB) which have so far shown potential as a complementary tool that can be used both inside and outside peoples’ home, thus, protecting people even when they are not yet protected by mosquito nets. Although they are still under trials, previous studies have shown promising results as highlighted in this randomized control trial by Mohammad Traore and colleagues.
In addition, the use of novel genetic control tools such as gene drives and sterile insect techniques to suppress the population or replace mosquitoes with recessive lethal genes using the novel CRISPR/Cas to manipulate the mosquito genome has potential applications in malaria control.
Other potential strategies include use of Wolbachia to induce cytoplasmic incompatibility in mosquitoes. This has been shown in aedes mosquitoes to control dengue and more studies are required to check their applicability in anopheles mosquitoes.
Innovative technologies such as the use of drones to map mosquito breeding sites are also taking shape. One study that was led by Michelle Stanton and friends in Malawi highlighted the role drones can play in the fight against malaria by providing fine scale mapping of water bodies and giving an understanding of the role of water bodies such as dams in malaria transmission in the dry season. Other future applications of drones include drone assisted insecticide spraying, collecting water samples from breeding sites using drones and many other applications.
25 April each year is World Malaria Day, where the burden of the disease and the need for control and elimination are highlighted. This year, World Malaria Day was commemorated under the theme ‘harness innovation to reduce the malaria disease burden and save lives”. This theme has come at a time when novel and innovative tools are more than needed, calling for researchers, governments and all stakeholders to hold hands, put more resources, innovation and energy into the fight of this debilitating historical disease. I long for the day when we will celebrate world malaria history day on 25th April.