What's New in the Fight Against Malaria?
This article was originally published on Aug. 7, 2022 and has been updated by the author.
has plagued human populations for millennia. Caused by species of Plasmodium parasites, which spread to, and between, humans through the bite of Anopheles mosquitos, malaria triggers symptoms ranging from fever and nausea to organ failure and severe anemia. The disease is endemic to tropical and subtropical regions across the globe, with in sub-Saharan Africa. Pregnant women and young children are the most vulnerable to infection—. If they survive, some children will suffer repeat infections.
Though there has been progress toward mitigating this deadly disease, the battle is far from over. Due in part to the COVID-19 pandemic, which disrupted disease surveillance and control efforts, the has risen. Yet, “even before the pandemic, progress [on controlling malaria] had sadly stalled,” Dr. Mehreen Datoo, a clinical research fellow and Ph.D. student at , said in a talk given at ASM Microbe in June 2022. The , and include inadequate access to quality health care and funding.
What Methods Are Currently Used to Prevent Malaria?
, like insecticide-treated nets and indoor residual spraying of insecticides, are integral to malaria control efforts; they prevent Plasmodium-harboring mosquitoes from feasting on humans. The prophylactic administration of full courses of anti-malarial drugs, known as , is another technique used to thwart infections. , including intermittent preventive treatment in pregnancy and seasonal malaria chemoprevention, which is given to children under 5 years of age during the malaria season.
These management strategies are not perfect. The emergence of insecticide-resistant mosquitos (), could dampen the efficacy of existing vector control methods. For example, chemoprevention , which could limit its power in the future. Taking steps toward eliminating—and, perhaps one day, eradicating—malaria will require expanding and diversifying the collection of tools within the world’s malaria-fighting toolkit.
New Tools: Vaccines, Drugs and More
Vaccines
For Datoo, promising change comes in the form of vaccines. Over the past 20 years, there has been in the development of malaria vaccines targeting different stages of For instance, target Plasmodium merozoites, the form of the parasite that replicates in red blood cells and causes malaria symptoms.
Other vaccines, called pre-erythrocyte vaccines, target proteins on Plasmodium sporozoites residing in the liver, thus halting their eventual transformation into merozoites that enter the bloodstream. The most successful malaria vaccine to date, , is of the pre-erythrocyte variety. It targets circumsporozite protein (CSP), the .
demonstrated that 4 doses of RTS,S/AS01 showed 36.3% reduction in malaria cases in children 5-17 months of age over a 3-4-year period. Follow-up studies examining vaccine efficacy in 500,000 children in Malawi, Ghana and Kenya with a 30% and 21% reduction in severe malaria and hospitalizations, respectively.
“When you think about the numbers of children who die of malaria each year, these numbers make an impact,” Datoo said.
. However, Datoo noted, “at the moment, there is the worry that supply may be an issue.” The of 15 million RTS,S/AS01 doses per year falls far below the expected demand of over 80 million doses annually. Development of additional vaccines will be important to fill in the gaps. One promising example is , a pre-erythrocytic vaccine also targeting CSP that Datoo shepherded through the clinical trial pipeline. In a including 4,800 children in 4 African countries, the vaccine . Based on the promising data, in October 2023, WHO for prevention of malaria in children; the vaccine is expected to become available to countries in mid-2024.
Drugs
Though vaccines have captured the most attention as new, viable tools for malaria prevention, there have also been developments in the field of preventive drugs. For example, a single-dose, dispersible form of the anti-malarial drug, tafenoquine, (responsible for between 4 and 5 million infections each year) in children aged 2 years and up. The formulation, which can be dissolved in water, than the 7-14 day course of pills approved for adults. Researchers that causes enzymes within Plasmodium parasites to self-destruct. The compound showed potent parasite-killing powers in animal models and may be a steppingstone toward development of new anti-malaria drugs for humans.
Vector Control
Progress has also been made toward improving the efficacy of existing , such as modifying mosquito nets to combat insecticide resistance, as well as developing new tactics, like . Moreover, it was demonstrated that Anopholes mosquitoes (the species that spread malaria) can be . In Aedes mosquitoes, the vector for yellow fever, Dengue fever and Zika fever, Wolbachia the viruses that causes these deadly infections. In fact, Wolbachia-infected Aedes mosquitoes are . Could a similar approach be used for malaria? Though it was long-believed Anopholes mosquitoes did not harbor Wolbachia bacteria, the finding that they can may open doors for new preventive tactics. More research is required to determine if, and how well, Wolbachia can prevent malaria transmission.
Moving Forward
Is a future without malaria possible? Strategies to combat the disease are as complex as the lifecycle of the parasite that causes it. One thing is clear: there is no time to waste.
“My talk has been half an hour,” Datoo said. “And, in that time, 50 children have died from malaria.”
Ultimately, approach using old and new methodologies, of malaria cases and changes in transmission, will be required to reduce the disease burden across the globe.
Research in this article was presented at ASM Microbe, the annual meeting of the American Society for °®¶¹´«Ã½, held June 9-13, 2022, in Washington, D.C.
Peering into history can help put recent malaria cases in context. Lessons learned can be applied to other areas battling endemic malaria and surveillance and prevention efforts around the world.
