BY SOLA OGUNDIPE
In what may be described as a counter-intuitive move, a team of researchers has proposed a theory that letting mosquitoes grow up and breed may be part of the solution to tackling the devastating impact of malaria.
The bizarre theory which was announced shortly before the 2011 World Malaria Day on Apil 25, is the brainchild of researchers led by Dr Stephen Gourley of the University of Surrey’s Mathematics Department.
The scientists, who have utilised mathematical modelling to examine why conventional insecticides used against the insects that transmit the disease responsible for millions of deaths a year, argue that they can quickly become ineffective in areas of intensive use. Their answers, which may lead to unprecedented advances in malaria control, are currently the talk of the scientific world.
Mosquitoes are known to develop resistance to commonly used insecticides surprisingly rapidly. Research shows that spraying young mosquitoes simply imposes intense selection pressure favouring the resistant insects.
Hence, biologists have suggested that a new kind of late-acting insecticide could slow this process and lead to insecticides which would remain effective over a much longer period of time.
The strategy, it was gathered, aims to exploit the fact that mosquitoes only become able to infect humans with the malaria parasite late in their lifetime, due to a relatively long latency stage. This means that the delayed action insecticide doesn’t result in increased infection rates while the younger insects remain alive.
Gourley’s team used mathematical models to predict the effect of an insecticide that only acts after a time delay, once the mosquitoes have laid their eggs.
This results in a lessened selection pressure on resistant mosquitoes that evolve much more slowly.
This technique, it is believed, could result in vastly improved malaria control in areas where resistance to current insecticides is common with mosquitoes.
However, it could mean a rise in the number of annoying but non-malarial mosquitoes.
The trade-off is between effective prevention of malaria transmission by mosquitoes and living with mosquito bites involving no malarial transmission.
Malaria kills over one million people every year and remains one of the leading causes of child mortality in Africa.
Conventional insecticides, the argue, kill mosquitoes as soon as they are exposed, but while this approach works well in the short term, its indiscriminate action speeds up the evolution of the insect towards insecticide resistance.
In particular, because the insecticide acts on female mosquitoes before they lay eggs, this causes intense selection pressure towards insecticide-resistant females who then pass on this resistance to their offspring.
In 2009, scientists discovered that killing only the older mosquitoes is a more sustainable way of controlling malaria. Thy said the approach may lead to evolution-proof insecticides that never become obsolete.