Only one solution to malaria eradication: Pyrethroid?

Mosquito on skin

Alec Morton Professor Alec Morton
Management Science 
 Dr Eve Worrall

Dr Eve Worrall
Liverpool School of Tropical Medicine 

25 April 2017

Only one solution to malaria eradication: Pyrethroid?

Imagine that at your next family gathering, you discover that one of your elderly relatives has invested the entire lump sum from his pension in a venerable British retailer.  Even if you do not regard yourself as a particularly savvy investor you might be concerned about his judgement and his long-term financial prospects.  The point here is not that the company in question will fail, but that if it does, your relative will find her/himself in very difficult financial circumstances. 

All our eggs in one basket?

It might be surprising, therefore, to learn that humanity currently takes a similar approach to investment in the battle with one of its most ancient enemies.  The malaria parasite, which currently kills just under half a million people (mostly children) a year, is transmitted by mosquitos.  As most mosquitos feed at night, one of the most effective strategies in preventing malaria is to provide people in at-risk areas with insecticide treated bednets.  However, there is only one insecticide, pyrethroid, which is currently authorised for use on insecticide treated blankets.

Resistance – and death

Why is relying on a single insecticide problematic? After all, we rely on a single mineral, fluoride, to protect our teeth.  The reason to be concerned is because of the phenomenon of resistance.  Through natural selection, mosquito populations can evolve to be resistant to pyrethroid, i.e. the pyrethroid loses its ability to kill them.  There is some evidence (for example from Mexico in the mid-noughties) that mosquito populations can reach a tipping point, where failure of the insecticide rapidly becomes widespread and irreversible.  (In the same way, after a few missteps, a once respected company may find itself facing bankruptcy).  Thus, relying on exclusively pyrethroid is more like our relative’s unwise investment decision than might at first sight be apparent.

Addressing malarial market failures

Why has the market not provided new insecticides?  Economists study situations where markets do not exist or do not work properly: the general term for these situations is market failure.  Several reasons for market failure exist, and many can be seen in the case of insecticide treated bednets. Those most at risk of malaria live in the poorest countries in the world and are often unable to afford bednets. To improve health equity and increase access to this life saving tool, almost all of Africa’s bednets are financed by international development assistance. When someone uses an insecticide treated bednet they are not only protecting themselves from mosquito bites; the insecticide kills mosquitoes and protects non-users; transforming it into a public health intervention.

At the same time each pyrethroid treated bednet contributes to the development of resistance, but the price paid for pyrethroid nets does not fully capture the social disbenefit associated with its contribution to the evolution of resistance.  A benefit or disbenefit not borne by the purchaser and not reflected in the price is called a positive or negative externality.  (By analogy consider the positive externality created by buyers of electric rather than diesel cars, reducing air pollution for all of us, or the negative one of chewing gum manufacturers who can offer low prices only because government cleans up their product from the nation’s pavements.)

In the short term the artificially low bednet price is good, as it means more people can receive bednets for a given budget, however, in the long term a more expensive strategy involving use of multiple insecticides could slow the development of resistance and be more beneficial. To achieve that we need to create a market for a wider range of safe, effective and cheap insecticides to use on bednets.

Lessons from antimicrobials?

Similar market failures exist in the market for antimicrobial drugs, and many have argued for government intervention in the pharmaceutical markets to “unblock the pipeline” and encourage firms to create more innovative antimicrobials, as well as encouraging responsible use of existing antimicrobials.  Indeed, David Cameron’s government commissioned an influential review by Lord Jim O’Neill, a former Goldman Sachs executive, to examine ways in which this could be done, and the issue of antimicrobial resistance has been debated in recent times at the World Health Assembly, the UN General Assembly and the G20. 

Better economic thinking, better policy and better outcomes

Unfortunately both the economic thinking and the policy awareness around insecticide resistance are not as nearly as developed for insecticide resistance as they are for antimicrobial resistance.  Yet in the case of insecticide resistance, the stakes are also high and the issues complex.  In our IPPI Policy Brief, based on a preliminary economic analysis, we make some recommendations which would represent a start in encouraging responsible use of pyrethroids and stimulating technical innovation, thus safeguarding our current and future global health against the scourge of malaria.

Tags: Health