2. Prevention - Risk Assessment

The components of malaria prevention are often described as the ABCD of malaria. All travellers to malarial areas need to:

1. be aware of the risk of Acquiring malaria infection (described in this chapter),
2. know how to avoid mosquito Bites (Chapter 3),
3. take Chemoprophylaxis, as appropriate (Chapter 3), and
4. understand the need to urgently seek medical advice for Diagnosis and treatment if they have a fever (Chapters 3, 6).

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

Risk of Acquiring Malaria

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, and 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. The information is based on assessments developed by the World Health Organization (WHO), the United States of America Centers for Disease Control and Prevention (CDC), and the International Association for Medical Assistance to Travellers (IAMAT) and is considered authoritative for decision-making related to travellers and malaria. It should be noted, however, that many factors, such as variation in reporting and surveillance, may significantly affect the reliability of this information. Further, substantial variability may occur within the geographic areas defined in Appendix I.

Malaria transmission occurs primarily between dusk and dawn, corresponding to the biting habits of anopheline mosquitoes. The risk of transmission is increased in rural areas and varies seasonally in many locations, often being higher around the rainy season. Transmission decreases with altitude and may not occur in highland areas (e.g., generally above 2000 m [6500 ft]) and is virtually nonexistent over 2500 m (8,000 feet) (see Appendix I for country-specific information on malaria risk and altitude).

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 Papua [Irian Jaya]) may be associated with significant risk of infection. Although difficult to measure and monitor, retrospective studies of large numbers of travellers have provided an approximation of malaria risk during a 1-month stay, without chemoprophylaxis, as follows^{(14, 15, 16)}:

• Oceania (PNG, Papua [Irian Jaya], Solomon Islands and Vanuatu) 1:20;
• Sub-Saharan Africa 1:50;
• Indian subcontinent 1:500;
• Southeast Asia 1:500;
• South America 1:2,500; and
• Central America and the Caribbean 1:10,000.

It is noteworthy that the highest risk areas for malaria are Oceania, Africa and, to a lesser extent, the Indian subcontinent, where the relative risks of travellers acquiring malaria vary from 50 to 200 times greater than low-risk areas for malaria⁽¹⁶⁾.

In the last decade, there has been further spread of drug-resistant malaria. As well, the emergence or re-emergence of infection, especially with P. Falciparum, has occurred in certain geographic areas. For example, large outbreaks of malaria have occurred on the Indian subcontinent, where an increasing proportion of malaria cases are due to drug-resistant P. Falciparum. In recent years, malaria has occasionally surfaced in tourists as a result of the immigration of malaria-infected people from a malaria-endemic area (Haiti) into tourist resort areas in parts of the eastern Dominican Republic⁽¹⁷⁾, Great Exuma Island of the Bahamas⁽¹⁸⁾ and Jamaica⁽¹⁹⁾, previously considered to be free of malaria transmission. Although these malaria outbreaks were successfully contained, they demonstrate the potential for malaria to rapidly emerge or re-emerge in previously malaria-free regions. Therefore, pre-travel health care providers need to continually monitor malaria travel health advisories and alerts.

Exposure Assessment

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. Factors to consider in determining risk of exposure include the following:

• level of endemicity in the area(s) covered by the travel itinerary;
• presence of Plasmodium Falciparum;
• duration of exposure;
• rural, periurban, urban travel;
• seasonality (rainy vs. dry);
• night-time exposure; and
• availability and likelihood of use of other interventions, e.g., personal protective measures.

CATMAT considers there to be minimal risk of malaria in urban centres of Southeast Asia, and Central and South America. Recommendations to the Canadian traveller concerning malaria prevention measures in these regions of low malaria transmission risk should take into consideration the estimated risk of acquiring malaria related to the risk factors listed above and the potential risks of malaria chemoprophylactic measures. Clinical judgment is recommended on a case-by-case basis. It is the responsibility of pre-travel health care providers to monitor travel health advisories and alerts (posted on PHAC and CDC websites) in order to maintain up-to-date information on malaria risks in specific destinations, as malaria risk can rapidly change even in regions normally considered of low risk. Regardless of the malaria chemoprophylaxis regimens used, CATMAT recommends the use of personal protection measures. Please refer to CATMAT's Statement on Personal Protective Measures to Prevent Arthropod Bites (http://www.phac-aspc. gc.ca/publicat/ccdr-rmtc/05vol31/asc-dcc-4/).

The distribution of drug-resistant malaria (see Appendix I) also forms part of the exposure assessment. Chloroquine-resistant P. Falciparum is widespread in all malaria-endemic areas of the world, except for Mexico, the Caribbean, Central America (west of the Panama Canal), and parts of the Middle East (including Egypt)^{(5, 20)}. P. Falciparum malaria resistant to chloroquine AND mefloquine has been confirmed on the Thai-Cambodia and Thai-Myanmar (Burma) border areas, as well as the western provinces of Cambodia, the eastern states of Burma (Myanmar), on the border between Burma and China, in Laos along the borders of Laos and Burma, and in southern Vietnam⁽²⁰⁾.

Host Assessment

The health of the individual (e.g., age, pregnancy, current medications and chronic illnesses such as HIV), must be considered in order to assess the risk of severe disease if malaria were to occur and in order to choose an appropriate antimalarial drug for chemoprophylaxis (see Chapter 4)⁽²¹⁾.

Travellers should be made aware that reliable malaria diagnostic and treatment options may not be available in many travel destinations⁽²²⁾. Self-diagnosis of malaria using symptoms only, without laboratory diagnostic testing, is considered suboptimal. However, some travellers going to more remote locations may have few options other than self-diagnosis and self-treatment (see Chapter 7).

The following elements should be addressed in an individual risk assessment: Exposure Assessment Is the traveller likely to be exposed to malaria? Will the traveller be in a drug-resistant P. Falciparum zone? Host Assessment Is the traveller at increased risk of severe malaria disease (e.g., a young child, asplenic individual, HIV infected, pregnant woman)? Are there any contraindications to the use of a particular antimalarial drug in that particular traveller? Will the traveller have prompt access to medical care (including preparation of blood films with sterile equipment and prompt, accurate interpretation) if symptoms of malaria were to occur?

Evidence-based medicine (EBM) recommendation	EBM rating
Travellers should receive expert advice concerning malaria risks and avoidance strategies(15).	B III
Malaria chemoprophylaxis is very effective and is recommended for travel to malaria-endemic regions(20).	A I
An assessment of malaria risk (level of malaria endemicity, duration of exposure, personal protective measures) is essential to educating travellers(15, 16).	B II
An assessment of the traveller's health is a priority in determining malaria risk(21).	B II
An assessment of the quality of, and distance to, medical and laboratory facilities must inform the counseling of the patient on malaria risk(23).	B II

 

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