Malaria prevention is rarely a top priority for agencies responding to a refugee crisis. Preventative strategies will only be effective if they place no extra demand on the emergency response. Research involving the London School of Hygiene and Tropical Medicine, HealthNet International, the Vestergaard Frandsen Group, Denmark, and the NGO, Mentor, assessed the usefulness of insecticide pre-treatment of the plastic sheeting used for temporary shelters.

Conflict, health service breakdown, insecurity and inaccessible populations often limit emergency responses to just basic humanitarian aid. However, insecticide treatment of canvas tents is an established method of malaria control in refugee camps. In recent years, plastic sheeting (polythene tarpaulins) has replaced canvas as the preferred shelter material for displaced populations in complex emergencies. It is cheaper to make and transport and easier to stockpile. Polythene sheeting can now be impregnated with pyrethroid insecticide (deltamethrin) during manufacture. Will this protect refugees against malaria?

Researchers used laboratory tests and study platforms in an Afghan refugee camp to compare the insecticidal efficacy of different plastic tarpaulin sheeting and tents:

• untreated
• sprayed with deltamethrin on the inner surface
• impregnated with deltamethrin during manufacture.

They found that:

• Both new and weathered treated sheeting kills 100 per cent of mosquitoes in the laboratory, compared with only 10 per cent for untreated polythene.
• In the field, mosquito mortality rates are 86-100 per cent for sprayed or impregnated tarpaulins and tents, but just five percent for untreated tarpaulin.
• However, less than 20 per cent of mosquitoes feed on the blood of humans under treated or untreated shelters. The majority of mosquitoes die unfed, presumably before making contact with the host.

Mosquitoes can easily pass through gaps in crudely-erected tarpaulin shelters. So treatment with insecticide does not reduce the proportion of mosquitoes that feed on humans. But if the majority of refugees in a camp use treated tarpaulins, large numbers of mosquitoes will die and malaria rates will drop through a mass effect rather than direct personal protection. Refugees receive free tarpaulins when they register in new camps, so coverage would approach 100 per cent. Sunlight speeds up the degradation of insecticides.

But the killing activity of the tarpaulin only needs to last as long as refugees use it as their main shelter. As a camp becomes established, refugees usually build their own homes using locally available materials. Other methods of malaria control, such as spraying and bed-nets, then become easier to use. The researchers also point out that treated tarpaulins may control the insects that cause other diseases, such as leishmaniasis (sandflies) and diarrhoea (flies): the biggest cause of death in refugee camps. However, further research will be required to demonstrate this possibility.

Source(s):
‘Insecticide-treated plastic tarpaulins for control of malaria vectors in refugee camps’, Medical and Veterinary Entomology 16: 404-408, by K. Graham, et al., 2002

Funded by: World Health Organisation; European Commission; UK Department for International Development; Gates Foundation; Vestergaard Frandsen Group, Denmark

id21 Research Highlight: 11 June 2003

Further Information:
Mark Rowland
London School of Hygiene and Tropical Medicine
Keppel Street
London WC1E 7HT
UK

Contact the contributor: mark.rowland@lshtm.ac.uk

London School of Hygiene and Tropical Medicine, UK

Torben Vestergaard Frandsen
Director of Development
Vestergaard Frandsen Group
Haderslevvej 36
6000 Kolding
Denmark

Tel: +45 75 50 30 50
Fax: +45 75 50 30 44
Contact the contributor: tvf@vestergaard-frandsen.com

Vestergaard Frandsen Group, Denmark

Other related links:
'Out of the frying pan… malaria among Afghan refugees in Pakistan'

'A small price to pay: preventing malaria in rural Afghanistan'

'Unsafe haven? The risk of malaria in refugee camps'

'Rolling back reality: making malaria control accessible to all'

'Netting the problem: how effective are insecticide-treated bednets against malaria?'

'Controlling malaria in times of emergency: East Timor’s experience'

See id21's health links page on infectious diseases