Scientists warn that mosquitoes are building up a resistance to insecticide-treated nets, writes Thalia Randall.
In 2007 a humble kebele (neighbourhood) in a small town in Ethiopia housed a community that was particularly house-proud. The hard-packed mud walls of their homes may have been weathered, but people hung baby-blue net curtains to cover the cracks.
Blue doilies adorned television sets and were placed beneath vases. In one home, a blue screen hid a kitchen hatch.
Yes, the townsfolk had a penchant for decorating – in blue. But what was behind it? Free blue mosquito nets. They served dozens of purposes in the kebele, but none as a barrier against mosquitoes.
Although nearly every household had two or three, wrote researcher Carol Baume, not a single one had been hung as a bed net.
“Respondents claimed that they were not given any information about what to do with the nets,” Baume said.
“Apparently, someone in the town started using the nets for curtains and decoration, and other families followed suit.”
Aaron Mabuza, the malaria control manager for the department of health in Mpumalanga, said that something similar was found during a follow-up project after bed nets were distributed in that province.
“Most [recipients] were not using the bed nets. After three years, some of the bed nets were still in [their packets],” he said.
Mabuza said there were two reasons for this. Firstly, there was relatively little malaria in the area and people did not see it as a threat.
Secondly, many people slept outside because of the oppressive heat, which meant there was nowhere to hang the net from.
Research published in this year’s April edition of the Tanzania Journal of Health made similar observations. It cited studies that found, “even when the nets are provided for free, substantial percentages of people did not use them”.
The reasons given for this were cultural beliefs and suspicion about the insecticide-treated nets.
One villager said: “We are told treated nets are able to kill mosquitoes for six months … even ticks cannot survive if they land on it. It must be so powerful, what if our young children touch it?”
Professor Lizette Koekemoer, head of the Vector Control Reference Laboratory at South Africa’s National Institute for Communicable Diseases, said that many people did not want to use them because they believed the insecticide on the nets could cause tuberculosis and other lung diseases.
A Tanzanian respondent claimed that “mosquitoes have become familiar to the insecticide. Hence the ngao [insecticide] doesn’t kill them any more”.
Exception not the rule
But, despite the alarming nature of these findings, statistics show that non-use is the exception, not the rule.
Baume said that the number of people misusing their nets was not significant and United Nations Children’s Fund malaria health specialist Valentina Buj said that “misuse is really much more over-reported than we are finding in the field”.
Last year, the World Health Organisation (WHO) reported that 96% of people who had access to bed nets used them.
Despite this, one of the beliefs held by non-users may be credible. Researchers suspect that insecticide-treated nets are inadvertently helping malaria-carrying mosquitoes to build up a resistance to the insecticide.
Professor Maureen Coetzee, head of the University of Witwatersrand’s Malaria Entomology Research Unit, said: “As the insecticide [on the net] declines, they [the mosquitoes] are only getting exposed to a tiny bit, and they survive. Then their progeny come along and they also only get a tiny bit, and so the resistance builds up and builds up.”
A field study in KwaZulu-Natal found that the South African strain of the malaria-carrying mosquito, Anopheles arabiensis, took only three months to develop a complete resistance to a tested insecticide.
Koekemoer said that, although “giving out thousands of bed nets sounds good in theory”, untested mass distribution of insecticide-treated nets was, in fact, “very dangerous”.
“Once you’ve selected for resistance, it is very difficult to reverse the situation,” she said.
Last year, the WHO also warned that “drug resistance is a major concern”.
The debate is not about the nets themselves, but rather about treating them with insecticide or not.
“I personally think that untreated bed nets are best,” said Koekemoer – a net that provides protection without a risk of increasing resistance.
Although Mabuza agreed, Buj said that “the effect of the insecticide is decreasing, but has not disappeared”. Therefore, it is still “vitally important” to continue to deliver insecticide-treated nets until new products are found.
A holistic approach
Whatever their differences, everyone agrees that any approach in the fight against malaria must confront the problem holistically.
Above all, the recipients of nets must be taught how to use them correctly.
Baume said there was a need for “standardised, accurate information” to be given out with each net.
Buj said that “effective information and improving understanding must be done with locally appropriate strategies. There is no one size fits all, and thus all avenues, especially creative and innovative strategies, must be used.”
As it turns out, the discussion is about a lot more than where to put a blue doily.
Mortality rates sharply lower
The World Health Organisation has released the following statistics drawn from 106 malaria-endemic countries.
In 2010, it found:
- There were 216-million cases of malaria;
- An estimated 3.3-billion people were at risk of malaria;
- An estimated 50% of households in sub-Saharan Africa had at least one bed net and 96% of people with access to a net were believed to use it;
- There were a total of 46 malaria-endemic countries in sub-Saharan Africa; and
- Malaria mortality rates in African regions had fallen 33% since 2000.