As humankind entered the 1980s, small pox was eradicated, and polio and cholera were in retreat. However, malaria was still impacting hundreds of thousands of people.
A group of scientists came up with an ingenious experiment. They started with 36 mosquito nets – some of which were for double beds and some were for single beds.
Half of these were soaked in Permethrin (a powerful insect repellent). And half had holes torn into the nets to simulate wear and tear. They expected most nets to be torn – and for the owners to not have enough money to replace them.
In sum, there were 9 nets each with combinations of treated/untreated and torn/intact. Those treated with Permethrin were all laid flat in the sun for 90 minutes and then installed in 24 huts.
These huts had mosquito traps – some were designed to catch mosquitos inside the house and some as they left.
Between 8pm-6am for 6 days a week, volunteers slept in the huts. Mosquitos were collected 3 times during the day and live mosquitos were kept under observation.
After 21 weeks, 4,682 female anopheles mosquitos (Malaria vectors) were collected.
The researchers were expecting the Permethrin treated nets to be very effective. However, they were skeptical about the performance of the torn nets.
The results were astonishing.
The Permethrin treated torn nets reduced mosquitos entering 70%, increased mosquitos leaving the hut from 25% to 97%, and reduced the blood meal between 20%-10%.
This was unexpected as these tears in the net were large. And what’s more, even after 5 months, the Permethrin was still highly effective
It proved to be a breakthrough. The widespread use of impregnated bed nets stopped Malaria mortality from increasing and started to decline. These nets were twice as effective as anti-malarial drugs and sprays… and were responsible for almost halving the death rate from Malaria.
This was such an elegantly designed experiment – a beautiful illustration of the scientific method in action.
H/T: How Innovation Works by Matt Ridley
