ARCHIVED - Supplement : Canadian Recommendations for the Prevention and Treatment of Malaria Among International Travellers

1. Introduction

Malaria is a common and serious infection caused by five species of the genus Plasmodium: Falciparum, vivax, ovale, malariae and knowlesi. Infections with P. Falciparum have the highest fatality rates, and infections caused by P. vivax and P. ovale can relapse from latent liver stages. P. knowlesi is a malaria species increasingly described in Southeast Asia and is noteworthy in having a primate reservoir^{(1, 2)}. All species of malaria are transmitted by the bites of infected female anopheline mosquitoes. Rarely, transmission may occur by blood⁽³⁾, by shared needle use or congenitally from mother to fetus⁽⁴⁾.

The disease is characterized by fever and «flu-like» symptoms such as myalgia, headache, abdominal pain and malaise. Rigors and chills often occur. The classically described alternate-day fevers or other periodic fevers are often not present. Malaria deaths are frequently the result of delays in the diagnosis and treatment of the infection^{(5, 6)}.

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 symptoms of malaria are non-specific, and diagnosis is not possible without microscopy of a blood film or an antigen detection test (rapid diagnostic test).

According to the World Health Organization (WHO), in 2005 3.2 billion people living in 107 countries and territories were at risk of malaria, resulting in approximately 500 million cases and 1 to 3 million deaths⁽⁷⁾. About 60% of malaria cases occur in Africa, 40% in Asia and less than 5% in the Americas. For P. Falciparum malaria specifically, the estimated region of distribution is 74% in Africa, 25% in Asia and 1% in the Americas⁽⁵⁾. It is estimated that each year 1 million Canadians travel to areas where they may be at risk of malaria, resulting in 350 to 1000 malaria cases and 1 to 2 deaths annually^{(6, 8, 9)}, although under-reporting is estimated to be 30% to 50%⁽¹⁰⁾. The majority of P. Falciparum cases imported into Canada are acquired in sub-Saharan Africa, whereas the majority of P. vivaxcases are acquired on the Indian subcontinent⁽¹¹⁾.

Figure 1. Map of malaria-endemic zones*

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

The Canadian Malaria Network (CMN), in collaboration with the Public Health Agency of Canada (PHAC) and Health Canada's Special Access Program, maintains supplies of intravenous artesunate and quinine at major medical centres across the country to facilitate rapid access to effective treatment for severe malaria. From June 2001 to March 2007, there were 88 cases (33% children) of severe or complicated malaria reported to the CMN, a mean of 14.3 cases per year. Most (56; 64%) had been born in a malaria-endemic country. Data on chemoprophylaxis were documented in 83 individuals, of whom only 23 (28%) reported using any, and in only less than 10% of these was it appropriate. There were delays in malaria management; only 20% presented to medical care within 24 hours of symptoms, and 37% waited more than 3 days before seeking medical care. Diagnosis was delayed more than 24 hours in 26%, and treatment was delayed more than 24 hours in 14 patients (18%)(12).

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 20% for those with severe malaria, even when the disease is managed in intensive care units⁽¹³⁾. Progression from asymptomatic infection to severe and complicated malaria can be extremely rapid, with death occurring within 36 to 48 hours. 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.