Bedbugs develop resistance to insecticide-treated bed-nets
Feb 24, 2003
A team of British and Tanzanian researchers have discovered that bedbugs are developing resistance to the insecticide used to treat the bed-nets that provide protection against malaria-transmitting mosquitoes.
A team of British and Tanzanian researchers have discovered that bedbugs are developing resistance to the insecticide used to treat the bed-nets that provide protection against malaria-transmitting mosquitoes.
The researchers are concerned that the spread of such resistance could reduce the willingness of villagers to use bed-nets, which have been found to be a highly effective and cost-efficient way of controlling malaria, particularly among young children.
The discovery was reported this week by Chris Curtis, a researcher at the London School of Hygiene and Tropical Medicine, to the annual meeting of the American Association for the Advancement of Science (AAAS) in Denver, Colorado.
Curtis told the meeting that when bed-nets were first introduced, one of their attractions to villagers in Africa was that the pyrethroid insecticide with which they are treated not only killed mosquitoes that came into contact with them, but also eradicated bedbugs (Cimex hemipterus).
A recent study carried out in Tanzania, however — whose results are published in the recent issue of the journal Medical and Veterinary Entomology — reveals that bedbugs are developing resistance to the insecticide in villages where treated bed-nets have been in use for several years.
“But we are very worried that the reappearance of these insects may seriously reduce the enthusiasm of villagers to use treated nets and to bring them annually for re-treatment,†said Curtis.
The study, which was carried out in collaboration with researchers from the Tanzanian National Institute of Medical Research, found circumstantial evidence that bedbug resistance to pyrethroids may spread more rapidly in villages where not all bed-nets have been treated.
Conversely, it found that bedbugs have not reappeared in a village in which nearly all the beds have been provided with treated nets for 14 years, suggesting that in certain circumstances it is possible to permanently eradicate the problem.
Curtis also reported to the AAAS meeting on the results of a separate survey of 28 Tanzanian villages, which had been provided with free bed-nets, as well as free annual re-treatment with pyrethroids. These villages have shown consistent reductions in the number of infective mosquitoes and the prevalence of both malaria fever and anaemia in babies and children between the ages of three and four.
Although benefits were less clear in older children — perhaps because of lower immunity to malaria resulting from fewer infections when they were younger — such children were “no worse off†than those without bed-nets. Curtis said these results appear to meet the concerns of those worried of a ‘rebound’ effect of reducing — but not eradicating — malaria transmission in highly endemic parts of Africa.
Curtis also challenged those who claimed that bed-nets were only effective if they were sold to villagers, who would therefore see them as an investment, and thus be more inclined to use them than if they were distributed and re-treated free of charge.
“We believe that marketing bed-nets and insecticides to villagers is neither equitable nor efficient, and that it is much preferable that organised, pro-active teams visit villages to provide treated nets for all beds free of charge, and to visit annually to re-treat the nets,†he said.
He pointed out that with bed-nets costing just a few dollars each, it would cost $500m a year to provide and regularly re-treat bed-nets in the whole of rural Africa, where about 90% of the world’s child deaths from malaria occur. Curtis added: “That is less than the amount spent on insecticides for cat flea control in the United States.â€
SciDEV.net
The researchers are concerned that the spread of such resistance could reduce the willingness of villagers to use bed-nets, which have been found to be a highly effective and cost-efficient way of controlling malaria, particularly among young children.
The discovery was reported this week by Chris Curtis, a researcher at the London School of Hygiene and Tropical Medicine, to the annual meeting of the American Association for the Advancement of Science (AAAS) in Denver, Colorado.
Curtis told the meeting that when bed-nets were first introduced, one of their attractions to villagers in Africa was that the pyrethroid insecticide with which they are treated not only killed mosquitoes that came into contact with them, but also eradicated bedbugs (Cimex hemipterus).
A recent study carried out in Tanzania, however — whose results are published in the recent issue of the journal Medical and Veterinary Entomology — reveals that bedbugs are developing resistance to the insecticide in villages where treated bed-nets have been in use for several years.
“But we are very worried that the reappearance of these insects may seriously reduce the enthusiasm of villagers to use treated nets and to bring them annually for re-treatment,†said Curtis.
The study, which was carried out in collaboration with researchers from the Tanzanian National Institute of Medical Research, found circumstantial evidence that bedbug resistance to pyrethroids may spread more rapidly in villages where not all bed-nets have been treated.
Conversely, it found that bedbugs have not reappeared in a village in which nearly all the beds have been provided with treated nets for 14 years, suggesting that in certain circumstances it is possible to permanently eradicate the problem.
Curtis also reported to the AAAS meeting on the results of a separate survey of 28 Tanzanian villages, which had been provided with free bed-nets, as well as free annual re-treatment with pyrethroids. These villages have shown consistent reductions in the number of infective mosquitoes and the prevalence of both malaria fever and anaemia in babies and children between the ages of three and four.
Although benefits were less clear in older children — perhaps because of lower immunity to malaria resulting from fewer infections when they were younger — such children were “no worse off†than those without bed-nets. Curtis said these results appear to meet the concerns of those worried of a ‘rebound’ effect of reducing — but not eradicating — malaria transmission in highly endemic parts of Africa.
Curtis also challenged those who claimed that bed-nets were only effective if they were sold to villagers, who would therefore see them as an investment, and thus be more inclined to use them than if they were distributed and re-treated free of charge.
“We believe that marketing bed-nets and insecticides to villagers is neither equitable nor efficient, and that it is much preferable that organised, pro-active teams visit villages to provide treated nets for all beds free of charge, and to visit annually to re-treat the nets,†he said.
He pointed out that with bed-nets costing just a few dollars each, it would cost $500m a year to provide and regularly re-treat bed-nets in the whole of rural Africa, where about 90% of the world’s child deaths from malaria occur. Curtis added: “That is less than the amount spent on insecticides for cat flea control in the United States.â€
SciDEV.net