Clinical review

Malaria: prevention in travellers

Ashley Croft, consultant in public health medicine. 

Ministry of Defence, London SW1A 2HB

AshleyCroft{at}compuserve.com

Definition: Malaria is caused by a protozoan infection of red blood cells with one of four species of the genus plasmodium: P falciparum, P vivax, P ovale, or P malariae.1 Clinically, malaria may present in different ways, but it is usually characterised by fever (which may be swinging), tachycardia, rigors, and sweating. Anaemia, hepatosplenomegaly, cerebral involvement, renal failure, and shock may occur.
Incidence/prevalence: Each year there are 300-500 million clinical cases of malaria. About 40% of the world's population is at risk of acquiring the disease. Each year 25-30 million people from non-tropical countries visit areas in which malaria is endemic,4 of whom between 10 000 and 30 000 contract malaria.5
Aetiology/risk factors: Malaria is mainly a rural disease, requiring standing water nearby. It is transmitted by bites6 from infected female anopheline mosquitoes,7 mainly at dusk and during the night. In cities, mosquito bites are usually from female culicene mosquitoes, which are not vectors of malaria.9 Malaria is resurgent in most tropical countries and the risk to travellers is increasing.10
Prognosis: Ninety per cent of travellers who contract malaria do not become ill until after they return home.5 "Imported malaria" is easily treated if diagnosed promptly, and it follows a serious course in only about 12% of people. The most severe form of the disease is cerebral malaria, with a case fatality rate in adult travellers of 2-6%,3 mainly because of delays in diagnosis.5
Aims: To reduce the risk of infection; to prevent illness and death.
Outcomes: Rates of malarial illness and death, and adverse effects of treatment. Proxy measures include number of mosquito bites and number of mosquitoes in indoor areas. We found limited evidence linking number of mosquito bites and risk of malaria.13
Methods: Clinical Evidence search and appraisal in November 1999. We reviewed all identified systematic reviews and randomised controlled trials (RCTs).
Question: What are the effects of non-drug preventive interventions in adult travellers?
Option: Aerosol insecticides
We found insufficient evidence on the effects of aerosol insecticides in travellers.