New insecticides are crucial in battle against malaria

Roger Bate | 19 Feb 2024
Insecticides are the most important preventative tool against malaria, dengue and filariasis. Even for yellow fever, where a vaccine exists, insecticides are needed to control common outbreaks.

Characteristics that make good public health insecticides (PHIs) are not necessarily shared by modern agricultural or industrial insecticides. For example, DDT (Dichloro-Diphenyl-Trichloroethane) was dropped as an agrochemical in the 1970s because it biodegrades slowly and accumulates in biological systems when widely used in agriculture.

Yet its persistence makes it a powerful PHI. When sprayed inside houses, DDT protects all inhabitants from malaria for approximately one year — no alternative lasts as long at the same cost. Even in places where mosquitoes are resistant to DDT's toxic actions, it deters mosquitoes from entering houses sprayed with the chemical.

Insecticide-treated nets (ITNs) primarily protect only the people sleeping under them and are less effective than generally assumed because ITN distribution does not equate with consistent use. And while the mass distribution of ITNs has undoubtedly saved thousands of lives, mosquitoes are becoming increasingly resistant to the insecticides used on them, partly because the same chemicals are used in farming. Recent studies have identified growing resistance in Benin and Uganda, where free net distribution has occurred for a decade.

We urgently need new insecticides that combine repellency and persistence with strong binding properties (for use with ITNs).

Stumbling blocks

Yet, while government donors and organisations such as the Gates Foundation and the World Bank spend billions on research into new vaccines and drugs, they invest very little in the search for new PHIs. The newest compound recommended by the WHO for malaria control, etofenprox, was made available in 1986.

The private sector has developed every major insecticide since 1940 — for agricultural or industrial purposes. Public funds played a part in early stage research, but private markets drove product development. The market for PHIs is about 1.3 per cent of the total insecticide market (US$400 million out of US$30 billion). So while most large companies who make insecticides — such as Bayer, and Syngenta — are pleased to sell PHIs, they lack financial incentives to develop products specifically for that sector.

And, according to a Boston Consulting Group report backed by the Gates Foundation, the cost of research and development in the agrochemical industry has risen 500 per cent over the past 20 years.

Opposition from environmentalists makes investing in the search for new PHIs even less attractive.

In 1993, the Pan American Health Organization banned the use of pesticides identified by influential environmentalists and in 1997, a World Health Assembly resolution called on WHO member states to reduce reliance on insecticides for controlling vector-borne diseases.

Environmental groups, led by Pesticide Action Network, regularly champion replacing insecticides with "environmentally sound and socially just alternatives". This often means reducing breeding opportunities for mosquitoes and using larvivorous fish to eat mosquito larvae, which can work — but only under specific circumstances. Exclusively relying on these techniques addresses the risks of man-made chemicals, but gives scant consideration to the far more dangerous disease threats. Yet aware of the implacable environmental community, aid groups have been reluctant to defend insecticide spraying.

Current efforts

The WHO has offered no leadership in the struggle to identify and invest in more effective insecticides. Its Pesticide Evaluation Scheme remains underfunded and slow in responding to the needs of the public health community.

The UN Stockholm Convention on Persistent Organic Pollutants and the Global Environmental Facility at the World Bank have paid lip service to finding new insecticides. But the Gates Foundation is the only organisation to have seriously supported the effort. In 2005, it gave US$50 million to the Innovative Vector Control Consortium (IVCC) — an international partnership between five research institutions in South Africa, United Kingdom and the United States — which aims to "develop new and better ways to control the transmission of insect-borne disease".

Promisingly, the initiative has begun investigating compounds to replace the current crop of insecticides, working with major manufacturers (notably Bayer and Syngenta) to bring new products to the market. But public documents indicate that the IVCC is not investigating repellency, which seems misguided.

Other than this initiative — which is dwarfed by the dollars donors spend on bed nets and treatment of insect-borne diseases every year — very little research is being done.

To encourage research, rich countries must urgently adopt measures similar to the Orphan Drug Act and priority review vouchers, both of which have helped attract investment in medicines for which there is no profitable market.

The credit crunch has made investment and risk-taking difficult. But if malaria deaths are to end, politicians, businessmen, celebrities and activists must devote their efforts to creating an environment that encourages investment in new PHIs.