At the beginning of the year, two of Ndzimandze’S grandchildren were bitten by Anopheles arabiensis mosquitoes, one of the key vectors of malaria in sub-Saharan Africa. The children showed all the usual symptoms of the disease, but when Ndzimandze brought them to the closest clinic they were misdiagnosed.

"After they came back home, I had a suspicion that it could have been malaria, but I was too busy keeping them hydrated," says Ndzimandze. As the symptoms worsened, she took the children to a hospital, where they were finally diagnosed with complicated malaria. The children survived, but they missed two school terms and are still struggling to recover.

A preventable killer

Malaria is a disease caused by parasites that are transmitted to people through the bites of infected female Anopheles mosquitoes. Mosquitoes breed in stagnant, freshwater

environments, such as puddles, swamps or ponds. Despite its recognizable symptoms, including fever, chills, severe headache, nausea and vomiting, and the fact that the disease is curable given correct diagnosis and treatment, over 400,000 people still die of malaria every year.

Africa carries a disproportionately high share of the global malaria burden. In 2017, the region was home to 92 per cent of an estimated 219 million cases of malaria worldwide, as well as 93 per cent of all malaria deaths---most of them preventable.

In eSwatini, malaria transmission is seasonal and unstable, with substantial variations in infection rates from year to year, depending on climate and other factors. Even in the best of years however, about 30 per cent of the tiny nation's 1.3 million people are at risk.

Over the past 10 years, eSwatini has achieved a drastic reduction in the incidence of malaria. However, this progress has come at a cost---the ongoing use of DDT (or Dichlorodiphenyltrichloroethane), a dangerous persistent organic pollutant targeted for elimination under the Stockholm Convention.

DDT has been linked to cancer in humans and is acutely toxic to fish and marine invertebrates. Mass spraying of DDT has also seen rapid growth in mosquito resistance to the chemical in some regions, as has the overuse of pyrethroids and other DDT alternatives.

Because of its high stability and persistence, decades of DDT use around the globe mean toxic residues can now be found everywhere, from the open oceans to Himalayan glaciers, with the chemical even appearing in polar bear populations in the Arctic and penguin colonies in Antarctica.

While DDT is still permitted for use in indoor vector control where there are no affordable alternatives, governments and international actors have been fighting to phase out the chemical since the 1970s. Today, only 17 countries worldwide---13 of them in Africa---still use DDT to control insect-borne diseases.

Eco-friendly alternatives to toxic solutions

"While DDT use has been phased out across much of the world, a number of countries in Africa have been faced with the stark choice of either continuing to use DDT or allowing the incidence of malaria to increase unchecked," United Nations Environment Programme (UNEP) chemicals and waste expert Eloise Touni says.

"However, there are now proven chemical and non-chemical alternatives, including nature-based solutions, alternative and less hazardous chemicals, and integrated approaches that offer non-toxic ways to protect people from malaria and other vector-borne diseases."

Touni oversees the Global Environment Facility-funded Demonstration of Effectiveness of Diversified, Environmentally Sound and Sustainable Interventions, and Strengthening National Capacity for Innovative Implementation of Integrated Vector Management for Disease Prevention and Control in the WHO AFRO [World Health Organization's Regional Office for Africa] project (AFRO II). In partnership with the World Health Organization (WHO), the project is supporting 15 African countries that still rely on DDT, or are considering reverting to it, to introduce newer and safer interventions for disease vector control.

In eSwatini, the project is experimenting with biological larviciding as an alternative to DDT, using the Bacillus thuringiensis israelensis bacteriu, or 'Bti'. A naturally occurring soil bacterium, Bti contains spores that produce toxins that specifically target the larvae of certain insects---including mosquitoes.

By targeting mosquitoes before they reach adulthood---and thus begin both breeding and spreading malaria and other diseases, strategic larviciding can have a significant impact on mosquito populations, as well as reducing the need for the use of toxic insecticides at the household level.

Local proof, global potential

With no toxicity to people or documented resistance to the bacterium as a larvicide, the AFRO II project team is championing Bti as a powerful new weapon in Africa's fight against malaria.

AFRO II project partner the International Centre for Insect Physiology and Ecology has mapped eSwatini, identifying mosquito breeding areas for biological insecticide applications.

"We selected villages with malaria cases and local transmissions, to which we add a 1 km buffer zone that covers the possibility of mosquitoes flying in," says the Centre's Postdoctoral Fellow Theresia Estomih Nkya.

After the areas surrounding the villages are mapped, the project's field workers sample local aquatic environments for Anopheles mosquito larvae and identify areas to be treated with Bti.

"We hypothesize that malaria cases will be significantly reduced thanks to the intervention," Nkya says. "It would reduce the need for the spraying of DDT and other toxic chemicals in people's homes, a win-win for everyone".

With the effectiveness of Bti in reducing mosquito larval populations already proven in other countries, the AFRO II team have high hopes for this nature-based solution to one of the world's most lethal vector-borne diseases.

"Biological insecticides have huge potential to both complement and provide an alternative to synthetic chemical larvicides," UNEP's Touni says. "From malaria to other mosquito-borne diseases like zika, dengue and chikungunya, eco-friendly solutions like Bti have the potential to help save lives worldwide."

The Demonstration of Effectiveness of Diversified, Environmentally Sound and Sustainable Interventions, and Strengthening National Capacity for Innovative Implementation of Integrated Vector Management for Disease Prevention and Control in the WHO AFRO Region project (AFRO II) is working with partners across 15 African countries to introduce non-toxic alternatives to chemical disease vector control.