Supplement

Canadian Recommendations for the Prevention and Treatment of Malaria Among International Travellers

1. Introduction

Malaria is a common and serious infection caused by four species of the genus Plasmodium: Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale, and Plasmodium malariae. Infection with P. falciparum can be fatal, and infections caused by P. vivax and P. ovale can relapse from latent liver stages. All species of malaria are transmitted by the bite of an infected female Anopheles mosquito. Rarely, transmission may occur by blood transfusion, by shared needle use, or congenitally from mother to fetus. The disease is characterized by FEVER and "flu-like" symptoms such as myalgias, headache, abdominal pain, and malaise. Rigors and chills often occur. The classically described alternate-day fevers or other periodic fevers are often not present. Severe malaria due to P. falciparum may cause seizures, coma, and renal and respiratory failure, and may lead to death. Malaria deaths are frequently the result of delays in the diagnosis and treatment of the infection.

THE SYMPTOMS OF MALARIA ARE NON-SPECIFIC, AND DIAGNOSIS IS NOT POSSIBLE WITHOUT A BLOOD FILM.

The widespread resistance of P. falciparum to chloroquine has complicated the prevention and treatment of malaria. Drug-resistant strains of malaria are now common in much of the world. The maps in Figures 1a and 1b indicate the geographic distribution of P. falciparum malaria based on patterns of resistance. These regions require frequent updating as the malaria situation continues to evolve.

Figure 1a
Map showing malaria-endemic zones worldwide*

*Visual aid only, see Appendix I, for specific country recommendations.

Figure 1b
Enlarged map of China and Thailand showing patterns of malaria resistance*

*Visual aid only, see Appendix I, for specific country recommendations.

As noted in Figure 2, the number of reported cases of malaria in Canada peaked in 1997 and then decreased. It is anticipated that the cyclical increase in malaria cases will recur. However, it is estimated that only 30% to 50% of cases are reported to public health agencies, and therefore the true number of imported cases into Canada is likely to be substantially higher. This assumption is supported by a recent study of laboratory reporting in two Canadian provinces, where only 52% to 71% of confirmed laboratory cases were reported to Health Canada. Canada's rate of imported malaria continues to be 3 to 10 times the per capita rate of the United States, which may reflect true differences in risk or may be a reporting artefact.

Figure 2
Trends in reported malaria cases, Canada, 1993-2002

* Note 2001 and 2002 numbers are preliminary and subject to change.

The majority of imported P. falciparum cases continue to be acquired in subSaharan Africa, and the majority of P. vivax cases are acquired in the Indian subcontinent. The increased number of Canadian malaria cases has been associated with severe and fatal cases. There have been 11 malaria deaths reported since 1997, all due to P. falciparum. As well, since June 2001 there have been 25 cases of malaria requiring parenteral quinine for treatment of severe or complicated disease. Factors contributing to all of these severe and fatal cases were noncompliance with or failure to use appropriate chemoprophylactic agents, delay in diagnosis and treatment, and incorrect therapy once a diagnosis had been reached.

Almost all malaria deaths in travellers are due to P. falciparum. The overall case-fatality rate of imported P. falciparum malaria varies from approximately 1% to 5% and increases to 30% for those > 70 years of age. Progression from asymptomatic infection to severe and complicated malaria can be extremely rapid, with death occurring within 36 to 48 hours. The fatality rate of severe malaria is > 20% even when the disease is managed in modern intensive care units. The most important factors that determine patient survival are early diagnosis and appropriate therapy. The majority of infections and deaths due to malaria are preventable.

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