Highland locations in east Africa are prone to malaria epidemics. Transmission rates are low, with big variations within and between years. The risk of malaria is equal across age groups as people have little or no immunity. But does every household have a similar risk?

Malaria risk within a geographical area depends on mosquito distribution, human contact with mosquitos and human risk factors. Risk factors identified for malaria include distance to known mosquito breeding sites, household construction and crowding, and personal protection measures against mosquito biting. These in turn are influenced by the environmental landscape and socio-economic status. Researchers from London School of Hygiene and Tropical Medicine investigated the impact of some of these factors on malaria risk during a recent epidemic in the highlands of Nandi District, Western Kenya.

Through active case surveillance in three schools for ten weeks during a malaria outbreak, researchers found 129 cases which were matched to 155 controls. Analysis of human, household and environmental factors revealed that:

• Risk of malaria is higher in children who are underweight. This may be a biological effect or a marker for another socio-economic difference. There is no link between risk of malaria and stunting (chronic malnutrition).
• More malaria cases occur at altitudes below 1750 m. Altitude is linked to differences in temperature and availability of temporary freshwater pools for mosquito breeding.
• Malaria is less common in household of higher socio-economic status or where drugs are kept at home.
• Neither age nor sex is a risk factor.
• Differences in the construction or smokiness of a child’s room are not linked to risk of malaria. However, there is relatively little variation in house construction in the study area.
• Malaria risk seems to be unrelated to use of personal protection, but this is probably because use of bed nets and insect repellents is very low.

The researchers recommend that access to quick and effective treatment and targeted mosquito control, including residual house spraying, remain the priorities for effective malaria control in highland areas. Effective control requires good knowledge of risk patterns over time as well as space.  Appropriate tools for epidemic prediction and early detection will be vital to appropriately target malaria interventions.

Source(s):
‘Spatial clustering of malaria and associated risk factors during an epidemic in a highland area of western Kenya’, Tropical Medicine and International Health 9(7): 757-766, by S. Brooker, et al., 2004
HINARI subscribers can access the full-text article here. Full document.

Funded by: Bill and Melinda Gates Foundation, DBL - Institute for Health Research and Development, World Bank, Wellcome Trust

id21 Research Highlight: 20 October 2005

Further Information:
Simon Brooker
Department of Infectious and Tropical Diseases
London School of Hygiene and Tropical Medicine
Keppel Street
London WC1E 7HT
UK

Contact the contributor: simon.brooker@lshtm.ac.uk

London School of Hygiene and Tropical Medicine, UK

Jonathan Cox
Department of Infectious and Tropical Diseases
London School of Hygiene and Tropical Medicine
Keppel Street
London WC1E 7HT
UK

Contact the contributor: jonathan.cox@lshtm.ac.uk

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