Malaria Risk Assessment for Travelers
The risk for a traveler contracting malaria differs substantially from region to region and from traveler to traveler, even within a single country, based upon travelers’ behaviors and circumstances.
There is no accepted method of quantifying the risk and no numerical value for a risk threshold beyond which chemoprophylaxis is or is not recommended. Thus experience and judgment are required in assessing the factors described below to arrive at the best prevention strategy for the individual traveler.
A travel or tropical medicine specialist can be an excellent source of guidance when making these decisions. Depending on level of risk, it may be appropriate to recommend no specific interventions, mosquito avoidance measures only, or mosquito avoidance measures plus chemoprophylaxis.
For the risk-averse traveler, remember that even in low risk situations, it only takes one bite from an infective female Anopheles mosquito to transmit malaria.
Questions to Ask When Assessing an Individual Traveler’s Risk
- For some areas with limited malaria transmission, where malaria cases occur sporadically and risk of infection to travelers is assessed as being very low, it is recommended that travelers use mosquito avoidance measures only, and no chemoprophylaxis should be prescribed.
- Regions associated with the highest estimated relative risk of infection for travelers are West Africa and Oceania. For these areas of intense transmission, exposure for even short amounts of time can result in transmission, and so chemoprophylaxis should always be used.
- Regions associated with moderate estimated relative risk of infection for travelers are the other parts of Africa, South Asia, and South America.
- Regions associated with lower estimated relative risk for travelers are Central America and other parts of Asia. There is considerable country-by-country variation, as well as variable transmission within countries. See the malaria information by country table for details.
Malaria transmission is not distributed homogeneously throughout all countries. Some destinations have malaria transmission occurring throughout the whole country, while in others it occurs in defined pockets. If travelers are going to the highly endemic pockets during peak transmission times, even though the country as a whole may be low transmission, this destination for this individual may be high risk.
In some countries with significant seasonal shifts in temperature or rainfall, malaria transmission intensity may decrease during the colder or drier months of the year. Based on knowledge of the climactic conditions in some sub-tropical or temperate destinations, travelers may choose mosquito avoidance measures only, for example, during the winter months.
It is important to assess factors such as the types of accommodations and activities as well as the reason and duration of travel as a part of the risk assessment. For example, short-term business travelers staying in air-conditioned hotels may be at lower risk than backpackers or adventure travelers.
Because malaria-transmitting mosquitoes are most active at night, include an assessment of the likelihood that the travelers might be spending time outdoors in the evenings for dining or entertainment. Longer durations of stay in a malaria-endemic area may also increase the chance that an individual might become infected.
Certain travelers have been shown to have greater risk of malaria infection. Particular care should be given to ensure an effective malaria prevention strategy for these travelers.
- The highest risk is associated with first- and second-generation immigrants living in nonendemic countries who return to their countries of origin to visit friends and relatives (VFRs). Ironically, VFR travelers often consider themselves to be at no risk because they grew up in a malaria-endemic country and consider themselves to be immune. However, acquired immunity is lost very quickly, and VFR travelers, especially those going to West Africa and India, should always use appropriate chemoprophylaxis.
More on: VFR Travelers.
- Malaria infection in pregnant women can be more severe than in nonpregnant women. Malaria can increase the risk for adverse pregnancy outcomes, including prematurity, abortion, and stillbirth.
More on: Traveling while Pregnant
For these reasons and because no chemoprophylactic regimen is completely effective, women who are pregnant or likely to become pregnant should be advised to avoid travel to areas with malaria transmission if possible. If travel to a malarious area cannot be deferred, use of an effective chemoprophylaxis regimen is essential. Depending on the destination, this is usually either chloroquine or mefloquine.