In the tropics, insects can transmit significant illnesses (such as malaria, dengue, yellow fever, chikungunya, Zika, and rickettsial disease), which may be potentially life threatening. These diseases are best prevented by personal protective measures. In some cases (e.g., malaria or yellow fever), a preventive drug or vaccine is also available, but it should never replace personal protection measures. Travelers to areas where insects that transmit these diseases may be present can help minimize their risk by following the insect precautions and protective measures discussed below.
Personal Protection Measures
- Wear clothing that covers as much skin as practicable.
- Apply a repellent containing DEET (concentration 30%–35%) or picaridin (concentration 20% or greater for tropical travelers).
- Picaridin products in the U.S. with a 20% concentration include Natrapel (Tendercorp) and Picaridin Insect Repellent (Sawyer). Picaridin is also known as Icaridin in some countries.
- Picaridin has a pleasant smell, which is an advantage over DEET.
- The repellent should be applied to all exposed, nonsensitive areas of the body. Frequent application ensures continuous protection.
- When both repellent and sunscreen are used, apply the sunscreen first, using a product with an SPF of 30 to 50; apply DEET on top of the sunscreen. Due to the decrease in SPF when using a DEET-containing insect repellent after applying sunscreen, travelers may need to reapply the sunscreen more frequently.
- The time of day and type of insects to be avoided determine when the repellent should be applied.
- Mosquitoes that transmit malaria (Anopheles species mosquitoes) are generally night biters. In risk areas, be especially vigilant in applying repellent from dusk to dawn.
- Mosquitoes that transmit dengue, chikungunya, Zika, and yellow fever (Aedes species mosquitoes) are generally day biters. In risk areas, be especially vigilant in applying repellent during daytime hours, especially during peak biting times during the early morning hours and again in the late afternoon.
- Mosquitoes that transmit West Nile virus and Japanese encephalitis (Culex species mosquitoes) are most active at dusk and again at dawn. In risk areas, be especially vigilant in applying repellent from dusk to dawn.
- Consider treating outer clothing, tents, and sleeping bag liners with permethrin (or other pyrethroid) when traveling in an area of very high risk for malaria or other mosquito-borne or tick-borne diseases.
- If not sleeping in a sealed, air-conditioned room, sleep under a permethrin-impregnated bed net when at high risk of malaria. Regularly check the net for rips and tears, and keep it tucked in around the bed at all times. Ensure that all open windows have insect screens.
- Use an aerosol insecticide before going to bed and a vaporizer device throughout the night.
- A smoldering pyrethroid coil can be used outdoors to reduce flying insects.
- In areas where tick-borne disease is a risk, perform a full body check at least once a day.
Insect Repellents and Insecticide-Treated Clothing
The most effective repellents contain DEET (N, N diethylmeta-toluamide) or picaridin (Natrapel, Picaridin Insect Repellent,Cutter Advanced, Cutter Advanced Sport, KBR3023, Bayrepel, Autan, (RS)-sec-butyl 2-(2-hydroxyethyl). Picaridin is now considered to have comparable efficacy and duration of protection to DEET at the same concentration. Both compounds have now been shown to be effective under actual field conditions in tropical countries against both Anopheles and Aedes aegypti mosquitoes.
The use of another repellent, IR3535 (3-[N-acetyl-N-butyl] aminopropionic acid ethyl ester; Bug Guard Plus), is more controversial; conflicting data exist over its effectiveness. IR3535 is recommended by WHO as equivalent to picaridin at the same concentration. IR3535 repellents can be used in children 6 months and older. In the U.S., IR3535 repellents are available in a range of concentrations up to 20%.
Duration of protection: With both DEET and picaridin, the duration of effectiveness increases as the concentration of repellent increases. With DEET, the effect on duration of protection plateaus at about 50% concentration. Products with less than about 20% picaridin or DEET have a relatively short duration of protection and should be discouraged for use in tropical travelers. The optimal concentration of DEET is considered to be 30% to 35%. When used by tropical travelers in appropriate concentrations (i.e., 20% or greater), picaridin should be applied every 4 to 6 hours. In the U.S., there are 2 products containing 20% picaridin: Natrapel (Tendercorp) and Picaridin Insect Repellent (Sawyer).
Use in children: Both DEET and picaridin-containing repellents can be used in children 2 months and older. The maximum concentration of DEET that should be used in children is 30%. No information exists on the maximum concentration of picaridin for children. Picaridin is more pleasant smelling than DEET.
Use in pregnancy and breastfeeding: Pregnant women and their babies are at special risk from the consequences of vector-borne diseases. Clothing should cover as much skin as possible, leaving only extremities, head, and neck exposed. DEET (up to 20% concentration), picaridin, and IR3535 can be used by pregnant and breastfeeding women but should be used sparingly over remaining exposed areas and washed off once indoors and when insect precautions are no longer necessary. Do not apply insect repellents to the nipple area to prevent ingestion by breastfeeding children. Small amounts of DEET are absorbed through intact skin. The use of DEET in the first trimester has not been well studied; however, no evidence exists that the use of DEET or picaridin by pregnant or lactating women poses a health hazard to unborn babies or children who are breastfeeding. No long-term follow-up studies beyond 1-year postexposure are available. DEET has been shown in 1 study to be safe in the second and third trimesters of pregnancy when used at concentrations up to 20%. Controlled-release formulations appear to last longer and require less frequent application.
Safety: DEET is effective against mosquitoes, ticks, fleas, and chiggers and is a remarkably safe insect repellent. Only 30 cases of severe toxicity have been reported among billions of uses over 30 years. Most cases of toxic encephalopathy or seizures were reported in young children in whom excessive amounts were used over prolonged periods. No long-term information is available on the use of picaridin, but toxicity tests in animals have shown it to be extremely safe.
An increasing number of botanical repellents containing eucalyptus, citronella, soybean oil, geranium oil, castor oil, and 2-undecanone are marketed. At present, insufficient evidence exists that these are adequate alternatives to DEET or picaridin.
The following precautionary measures can minimize the possibility of adverse reactions to insect repellents containing DEET or picaridin:
- Use repellents according to label directions.
- Apply repellents sparingly and only to exposed skin or clothing.
- Repellents should not be inhaled or ingested, and contact with the eyes should be avoided.
- Avoid applying repellents to portions of children's hands that are likely to have contact with eyes or mouth.
- Never use repellents on wounds or irritated skin.
- Wash repellent-treated skin after coming indoors if no further risk exists of exposure to insects.
- If a suspected reaction to insect repellent occurs, wash treated skin and seek medical attention.
- Pregnant and nursing women should minimize use of repellents because about 6% to 9% of the chemical is absorbed through the skin.
Travelers also should purchase a pyrethroid-containing flying-insect spray to use in living and sleeping areas during evening and nighttime hours.
For added protection against mosquitoes, bed nets and clothing may be soaked in or sprayed with permethrin. Permethrin is an insecticide licensed for use on clothing; when applied according to directions it can be effective on clothing for several months and on bed nets for half a year. Permethrin physically binds to the fabric, preventing absorption through the skin and allowing the fabric to be repeatedly washed without loss of effect. In some countries, deltamethrin liquid is available.
Use of brand names is for informational purposes only and does not constitute preference for one brand over another.