Malaria: prevention in travellers

British Medical Journal, July 15, 2000 by Ashley Croft

Interventions

Beneficial:

Insecticide treated nets

Likely to be beneficial:

Air conditioning and electric fans Mosquito coils and vaporising mats Smoke Insecticide treated clothing Protective clothing Topical insect repellants Doxycycline in adults Mefloquine Antimalaria drugs for airline pilots

Unknown effectiveness:

Aerosol insecticides Biological control measures Insect buzzers and electrocuters Chloroquine Chloroquine plus proguanil Atovaquone plus proguanil Pyrimethamine plus dapsone Vaccines Antimalaria interventions in pregnant women

Likely to be ineffective or harmful:

Amodiaquine Sulfadoxine plus pyrimethamine Insect repellants containing diethyltoluamide or doxycycline in children

Background

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.[2 3] 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 bites[6] from infected female anopheline mosquitoes,[7] mainly at dusk and during the night.[1 8] 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.[11 12] 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.

Benefits

We found no systematic review or RCTs. We found one questionnaire based survey of 89 617 European tourists returning from east Africa, which found no evidence that commercially available personal aerosol insecticides alone significantly reduced the incidence of malaria (P = 0.55).[14]

Harms

We found no reports of adverse effects.

Comment

None.

Option: Biological control measures

We found no good evidence for the effectiveness of biological control measures in preventing malaria, nor evidence of harm.

Benefits

We found no systematic review or RCTs. Observational studies based on mosquito counts have found no evidence that growing the citrosa plant and encouraging natural predation of insects by erecting bird or bat houses reduce bites to humans from infected anopheline mosquitoes.[14]

Harms

We found no evidence of harm.

Comment

The only known way to reduce the number of mosquitoes naturally is to eliminate sources of standing water, such as tree stump holes, and discarded tyres, cans, and bottles.[15]

Option: Air conditioning and electric fans

One large observational study in travellers found that air conditioning reduced the incidence of malaria. One small observational study found that electric fans reduced numbers of mosquitoes in indoor spaces.

Benefits

We found no systematic review or RCTs. One questionnaire based survey of 89 617 European tourists returning from east Africa found that sleeping in an air conditioned room significantly reduced the incidence of malaria (P=0.04).[14] One observational study of various antimosquito interventions in six experimental huts in villages in Pakistan found that fans significantly reduced catches of culicene mosquitoes (P [is greater than] 0.05) but did not significantly reduce catches of blood fed anopheline mosquitoes.[16]

Harms

We found no evidence of harm.

Comment

These studies support the finding that mosquitoes are reluctant to fly in windy conditions.[17]

Option: Insect buzzers and electrocuters

We found little evidence for the effectiveness of insect electrocuters and ultrasonic buzzers in preventing malaria.

Benefits

We found no systematic review and no RCTs with malarial illness as an outcome. Observational studies have found no evidence that insect electrocuters and ultrasonic buzzers reduce bites to humans from infected anopheline mosquitoes.[18 19]