The use of insecticide-treated mosquito nets (ITNs) can reduce illness and death from malaria in African children. This has prompted interest in developing mosquito net delivery and treatment programmes. In practice, however, selling subsidised ITNs is much easier than maintaining good re-treatment rates, especially when insecticide is distributed only through occasional visits of a project team.

Researchers from the London School of Hygiene and Tropical Medicine examined the views and habits of mosquito net users in Dar es Salaam, Tanzania. They found that people who regularly sleep under nets are sensitive to the effectiveness and durability of the insecticide. Net washing practices should be considered when designing strategies for the delivery of re-treatment. Where nets are washed frequently, treatment with a lower dose of insecticide after each wash should be considered.

Mosquito nets treated with a high dose of insecticide can be effective against malaria mosquitoes for at least six months. However, washing a treated net makes it less effective at killing or repelling mosquitoes. Regular re-treatment using low-dose insecticide could reduce the unit cost of each treatment and prevent the build-up of excessive insecticide deposits. But would mosquito net users perceive the low-dose treatment as effective?

The study investigated user perceptions of efficacy by comparing responses to bed-nets treated with different dosages of various insecticides. Findings include:

• The primary reason for regular use of bed-nets is to prevent nuisance biting although there is awareness of the link between mosquitoes and malaria.
• People who regularly sleep under bed-nets can distinguish between treated and untreated nets. They greatly appreciated the added benefits of ITNs.
• There is little concern over the safety of the insecticide, possibly due to endorsement by a respected authority.
• Treatment of bed-nets with high-dose insecticide is felt to have a dramatic effect on all mosquitoes - a perception which continues for at least eight weeks.
• Low-dose insecticide is seen as being less effective and effects wear off by the eighth week.
• Regular users tend to wash their nets at least monthly, primarily because dirty nets are seen as a health hazard and are socially unacceptable.
• Washing a treated net considerably reduces its perceived effectiveness against mosquitoes even if the original treatment was of a high dose.

These results question the wisdom of asking people not to wash their nets for six months, as many ITN projects do. It may be preferable to consider how the technology can be adapted to fit people's habits, rather than attempting to change them.

Organisers of bed-net treatment programmes in urban Africa could improve the chances of widespread adoption by:

• understanding the perceptions and practices of net users
• considering the more frequent application of lower doses of insecticide
• using an initial 'loading' dose that is high enough that the nets are perceived to be effective against nuisance biting mosquitoes
• commissioning further trials of user acceptability and biological effect to determine optimum insecticide dosages and re-treatment frequencies.

Source(s):
‘A new strategy for treating nets. Part 2: Users’ perceptions of efficacy and washing practices and their implications for insecticide dosage', Tropical Medicine and International Health 4 (3): 167-174, by J. Miller, C. Jones, S. Ndunguru, V. Curtis and J. Lines, 1999
HINARI subscribers can access the full-text article here. Full document.

Funded by: International Development Research Centre, Canada

id21 Research Highlight: 27 March 2002

Further Information:
Caroline Jones
ITD/DCVBU
London School of Hygiene and Tropical Medicine
Keppel Street
London, WC1E 7HT
UK

Tel: +44 (0) 20 7927 2649
Fax: +44 (0) 20 7580 9075
Contact the contributor: Caroline.Jones@lshtm.ac.uk

London School of Hygiene and Tropical Medicine, UK

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