[Table of Contents]

Volume: 26S2 - March 2000

2000 Canadian recommendations for the prevention and treatment of malaria among international travellers
prepared by the
COMMITTEE TO ADVISE ON TROPICAL MEDICINE AND TRAVEL (CATMAT)

2. PREVENTION

Four components of malaria protection should be discussed with the traveller:

a. the risk of acquiring malaria
b. personal measures to prevent mosquito bites
c. chemoprophylactic drugs (where appropriate)
d. the need to seek early diagnosis and treatment for a febrile illness

a. Risk of Acquiring Malaria

All travellers to malarial areas need to be aware of the risk of malaria infection, how they can best protect themselves, and the need to urgently seek medical advice if they develop a fever. Travellers staying overnight in rural areas may be at highest risk.

Malaria transmission occurs in most of sub-Saharan Africa and New Guinea; in large areas of Southern Asia; in parts of Southeast Asia, Oceania, Haiti, Central and South America; and in limited areas of Mexico, the Dominican Republic, North Africa and the Middle East. Appendix I provides country-specific information on malaria risk and recommended chemoprophylaxis. This information is derived from World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC) sources. While this is the most accurate information at the time of publication, many factors such as variations in local reporting rates and surveillance may significantly affect the reliability of these data.

Malaria transmission occurs between dusk and dawn, corresponding to the biting habits of the female Anopheles mosquito. The risk of transmission is increased in rural areas and varies seasonally in many locations, being highest at the end of the rainy season. Risk is proportional to the duration of an individual's exposure. Transmission decreases at altitudes above 2,000 metres (6,500 feet).

Travel to urban and tourist areas of Southeast Asia, and Central and South America are considered to entail minimal risk, whereas urban travel in other malaria-endemic regions, such as sub-Saharan Africa, the Indian subcontinent, and New Guinea (Papua New Guinea [PNG] and Irian Jaya) may be associated with significant risk of infection. In recent years, the spread of drug-resistant malaria and the prevalence of infection, especially with P. falciparum, have grown steadily. For example, malaria cases are at record levels on the Indian subcontinent, where an increasing proportion are due to drug-resistant P. falciparum.

Retrospective studies of large numbers of travellers have provided an approximation of malaria risk during a 1 month stay without chemoprophylaxis: Oceania (PNG, Irian Jaya, Solomon Islands and Vanuatu) 1:30 or higher, sub-Saharan Africa 1:50, Indian subcontinent 1:250, Southeast Asia 1:1,000, South America 1:2,500 and Central America 1:10,000. It is noteworthy that the highest risk areas for malaria are Oceania, Africa and, to a lesser extent, the Indian subcontinent.

b. Personal Measures to Prevent Mosquito Bites

ALL travellers to malaria-endemic regions are advised to use personal protective measures to reduce the risk of bites from Anopheles mosquitoes. Any measure that reduces exposure to the evening and night-time feeding female Anopheles mosquito will reduce the risk of acquiring malaria. Risk reduction behaviour includes remaining in well-screened or completely enclosed air-conditioned areas, sleeping under insecticide-impregnated mosquito nets, wearing clothing (ideally insecticide-impregnated) that reduces the area of exposed skin, and using insect repellent containing diethyltoluamide (DEET).

The use of insect repellent on exposed skin, particularly between dusk and dawn, is strongly recommended. Of the insect repellents registered in Canada, those containing DEET are the most effective. Although the concentration of DEET varies from product to product, repellency rates are largely equivalent. In general, higher concentrations protect for longer periods of time, but there is little advantage in the duration of repellency with DEET concentrations > 50%, and there may be additional risk of toxicity with higher concentrations. New microencapsulated products containing 33% DEET are registered in Canada, and they should provide 8 hours of protection. In rare instances, application of insect repellents with DEET has been associated with seizures in young children. Therefore, in children, DEET 10% or less should be applied sparingly to exposed surfaces only and washed off after the children come indoors (see section 4a, Malaria Prevention in Children).

ALL travellers at risk of acquiring malaria should be strongly encouraged to use insecticide-impregnated mosquito nets (e.g. permethrin, deltamethrin) unless their sleeping quarters are well-screened or otherwise protected from mosquitoes (A I - evidence-based medicine recommendations - see Appendix II).

Permethrin or deltamethrin-impregnated nets are significantly more effective in preventing malaria than untreated bed nets and are safe for children and pregnant women (A I - evidence-based medicine recommendations - see Appendix II). Impregnated bed nets are available in Canada for use only by travellers while outside of Canada. Permethrin treatment of clothing will also reduce the risk of malaria infection. (A I - evidence based medicine recommendation - see Appendix II). Currently, pyrethroid pesticides such as permethrin are not registered in Canada for use on clothing, and travellers should plan to purchase and apply these insecticides at their destination.

c. Chemoprophylactic Drugs (where appropriate)

Recommendations for chemoprophylaxis of malaria should be based on:

• individual risk assessment
• distribution of drug-resistant malaria
• safety and efficacy of chemoprophylactic regimens (See section 3, Chemoprophylactic Regimens.)

Individual risk assessment

Several factors need to be assessed when selecting an appropriate chemoprophylactic regimen before travel. The travel itinerary should be reviewed in detail and compared with known areas of malaria transmission within a country to determine the likelihood that the traveller will be at risk of acquiring malaria. The specific activities (e.g. rural travel, night-time exposure, unscreened accommodations) of the individual while in the malaria region(s) should be considered in estimating the risk of contracting malaria. The health of the individual (e.g. age, pregnancy, medication, and chronic illness) also needs to be considered in order to determine the risk of severe disease if malaria were to occur and to choose an appropriate antimalarial drug for chemoprophylaxis.

Distribution of drug-resistant malaria (see Figure 1 and Appendix I)

Chloroquine-resistant P. falciparum is now widespread in all malaria-endemic areas of the world, except for Mexico, the Caribbean, Central America (north of the Panama Canal), parts of China, and parts of the Middle East. P. falciparum malaria resistant to chloroquine AND mefloquine is still rare except in Thailand on the borders with Cambodia and Myanmar (Burma). Resistance to Fansidar^® (sulfadoxine-pyrimethamine) is now common in the Amazon basin, parts of sub-Saharan Africa and Southeast Asia. Chloroquine-resistant P. vivax is also becoming an important problem, particularly in Papua New Guinea, Irian Jaya, Vanuatu, Myanmar, and Guyana. Strains of P. vivax with reduced response to primaquine are now reported from widely divergent areas including Papua New Guinea, Somalia, and India.

CATMAT considers there to be minimal risk of malaria in urban centres of Southeast Asia and Central and South America. Malaria transmission falls at altitudes exceeding 2,000 metres (6,500 feet) and is virtually non-existent over 3,000 metres (10,000 feet).

d. Early Diagnosis and Treatment All travellers should be informed that malaria should be suspected if unexplained fever occurs during or after travel. Medical attention should be sought as soon as possible, and the traveller should request that a blood film be examined for malaria parasites. If the initial blood film is negative and the traveller remains symptomatic, then the blood film should be repeated in 12 to 24 hours. The most important factors that determine the survival of patients with falciparum malaria are early diagnosis and prompt initiation of appropriate treatment.

Appendix III provides a checklist for the preparation of travellers to malarial areas.

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