WASHINGTON — Long-term travelers to countries with high risk for malaria should use personal protective measures and chemoprophylactic regimens based on the risk factors they are likely to encounter, Patricia Schlagenhauf-Lawlor, Ph.D., said at the annual meeting of the American Society of Tropical Medicine and Hygiene.
Long-term travelers—defined by some guidelines as those who travel for more than 6 months—include people visiting friends and relatives, expatriates, occupational travelers such as military personnel, backpackers, and missionaries. These people can use precautions that range widely in their ability to prevent infection, including personal protection measures, stand-by emergency treatment, rapid tests for malaria, seasonal chemoprophylaxis, and continuous chemoprophylaxis, said Dr. Schlagenhauf-Lawlor of the World Health Organization Collaborating Centre for Travellers' Health at the University of Zürich (Switzerland).
Personal Protection Measures
A review of randomized trials concluded that insecticide-treated nets are effective in reducing childhood mortality and morbidity due to malaria (Cochrane Database Syst. Rev. 2005;
Clothing that has been impregnated with insecticides such as permethrin remain effective for several months. Shoes and protective (white or brightly colored) clothing also help to fend off mosquitoes, she added.
Among the mosquito repellents that are available in the United States, DEET (N,N-diethyl-m-toluamide) is still considered the best because it has been widely used and tested and is effective for more than 5 hours at concentrations of 20%. Children older than 2 months of age can use DEET, but it should be at concentrations of 10% or less.
The repellent picaridin (Bayrepel) at 19.2% concentration has been shown to cause less skin irritation while providing a level of protection similar to DEET, especially against the mosquito Anopheles gambiae. Picaridin has been approved by the Environmental Protection Agency and is safe for children older than 2 years, but studies have shown that the level and duration of protection varies between individuals, Dr. Schlagenhauf-Lawlor said.
Clinicians should avoid recommending natural oils such as citronella and eucalyptus because these oils provide only short-term protection, she said.
Mosquitoes generally prefer to bite adults rather than children, men rather than women, and large rather than small people. Some mosquitoes bite more often on the feet and ankles (A. gambiae) or face (A. atroparvus).
Travelers should learn what time of day the malaria-vector mosquitoes bite in the region they are traveling to. Bed nets may be ideal for travelers to Africa where A. gambiae is present, which prefers to feed indoors late at night. In the Amazon, repellents may work best against A. darlingi, which bites mostly in the early evening, she said.
But most long-term travelers have poor compliance with personal protection measures, Dr. Schlagenhauf-Lawlor noted. Experts consider a combination of at least four such measures to be adequate to protect against mosquito bites in high-risk areas for malaria. In a study of business travelers to high-risk areas in Africa, only 4% used four recognized methods of prevention, which include long clothes, air conditioning, repellents, insecticides, mosquito nets, and burn coils (J. Travel Med. 2003;10:219–24). Nearly all other travelers used some personal protection measures: Forty-three percent of the travelers used three measures, 25% used two, and 21% used one. Only 2% of tourists to high-risk areas in Africa used four personal protection measures (J. Travel Med. 1998;5:188–92).
Standby Emergency Treatment
The WHO defines standby emergency treatment (SBET) of malaria as the use of antimalarial drugs when malaria is suspected and prompt medical attention is unavailable within 24 hours.
For travelers in some areas, German and Swiss guidelines now recommend wider use of SBET instead of continuous prophylaxis.
“We recommend chemosuppression only when the benefit is 10 times greater than the risk of adverse effects,” Dr. Schlagenhauf-Lawlor said. “That means for most of our travelers, except for those in sub-Saharan Africa, we're recommending standby treatment and antimosquito measures.” This may be at odds with what American physicians would recommend.
Chloroquine and quinine have “very limited use” for SBET, while drugs such as mefloquine, atovaquone and proguanil (Malarone), and sulfadoxine plus pyrimethamine (Fansidar) are acceptable for SBET. Halofantrine (Halfan) is now contraindicated for SBET because of potential cardiac complications, she said.
The German and Swiss guidelines advise that chloroquine can be used for SBET in parts of Central America and the Middle East. The guidelines recommend that travelers to India use mefloquine. Travelers to the Southeast Asian countries of Myanmar, Thailand, Laos, Cambodia, and Vietnam should use Malarone for SBET because of multidrug resistant malarial strains, according to the guidelines.
The guidelines recommend continuous prophylaxis in Papua New Guinea, nearly all of sub-Saharan Africa, and in several provinces of Brazil. Continuous prophylaxis with mefloquine, doxycycline, or Malarone can be more than 90% effective if they are chosen correctly, but they cause “perceived or real” adverse events in more than 80% of patients. Many patients also fail to adhere to the dosing regimen for continuous prophylaxis and find it difficult to get the drug they need if they are traveling for more than a year, Dr. Schlagenhauf-Lawlor said.