Although vaccines or chemoprophylactic drugs are available against important vector-borne diseases such as yellow fever and malaria, travelers still should be advised to use repellents and other general protective measures against biting arthropods.
The effectiveness of malaria chemoprophylaxis is variable, depending on patterns of drug resistance and compliance with medication, and no similar preventive measures exist for other mosquito-borne diseases such as dengue or chikungunya. For many vector-borne diseases, no specific preventives are available.
The number of insect repellents available has been increasing, with several ac-tive ingredients now registered by the US Environmental Protection Agency (EPA). However, for travel to areas where the intensity of disease-transmitting vectors is high, it may be wise to use a product containing DEET or picaridin rather than an herbal product. DEET is the most studied repellent and travelers (military and civilian) have had the most experience with it.
General Preventive Measures
Tick-, mite-, and mosquito-borne parasitic and viral infections characteristically are diseases of “place” that are linked to known geographic or ecologic regions, and the amount of disease transmission in these areas often varies seasonally. Risk of infection increases when visiting areas of the world where these diseases occur and when epidemics are in progress. International travelers should consult CDC’s Travelers’ Health web page for alerts and information on regional disease transmission patterns that may change periodically (http://wwwn.cdc.gov/travel). Travelers to areas with identified risks should take the precautions described below to reduce the likelihood of acquiring a vector-borne disease. When possible, known foci of epidemic disease transmission should be avoided.
Travelers should be advised that exposure to arthropod bites can be minimized by modifying patterns of activity or behavior. Some vector mosquitoes are most active in twilight periods (i.e., dawn and dusk) or in the evening after dark. Avoidance of outdoor activity during these periods can reduce risk of exposure. Wearing long-sleeved shirts, long pants, and hats minimizes areas of exposed skin. Shirts should be tucked in. Repellents applied to clothing, shoes, tents, mosquito nets, and other gear will enhance protection.
When exposure to ticks, chigger mites, or biting insects is a possibility, travelers should be advised to tuck their pants into their socks and to wear boots, not sandals. Permethrin-based repellents applied as directed to clothing or camping equipment will enhance protection. Travelers should be advised to inspect themselves and their clothing for ticks, both during outdoor activity and at the end of the day. Ticks are detected more easily on light-colored or white clothing. Prompt removal of attached ticks can prevent some infections.
When accommodations are not adequately screened or air conditioned, bed nets are essential to provide protection and to reduce discomfort due to biting insects. Bed nets are most effective when treated with a repellent such as permethrin. Pre-treated, long-lasting bed nets can be purchased prior to traveling, or nets can be sprayed after purchase. The permethrin repellent will be effective for several months if the bed net is not washed. Bed nets should be tucked under mat-tresses. Aerosol insecticides can help to clear rooms of mosquitoes.
Repellents
Travelers should be advised that permethrin-containing repellents (e.g., Permanone) are recommended for use on clothing, shoes, bed nets, and camping gear, and are registered by the U.S. Environmental Protection Agency (EPA) for this use. Permethrin is highly effective both as an insecticide and as a repellent for ticks, mosquitoes, and other arthropods. Clothing treated according to label instructions should provide protection for up to 2 weeks and through several machine washings before re-treatment is required. Clothing pre-treated with permethrin is commercially available and should be used and washed according to the manufacturer’s instructions. There appears to be little potential for toxicity from permethrin-treated clothing. Permethrin-treated clothing should be supplemented with topically applied repellents to protect exposed skin.
The EPA has registered several active ingredients for use in personal repellents applied to skin. EPA registration of repellent active ingredients indicates the materials have been reviewed and approved for efficacy and human safety if applied according to the instructions on the label. These active ingredients are DEET (N,N-diethylmetatoluamide), Picaridin (KBR 3023), IR 3535, p-menthane 3,8-diole (PMD or oil of lemon eucalyptus) and oil of citronella. Two additional compounds are also registered as repellents by EPA (MGK-326, MGK-264); however, they are generally formulated with other active ingredients to enhance repellent activity and are not found alone in repellent products.
All the EPA-registered active ingredients have some repellent activity (1-5). Published data indicate that repellent efficacy and duration of protection vary considerably among products and among mosquito species and are markedly affected by ambient temperature, amount of perspiration, exposure to water, abrasive removal, and other factors. In general, higher concentrations of active ingredient in a repellent formulation provide longer durations of protection, regardless of the active ingredient. Lower concentrations are not as long lasting, offering short-term protection only and necessitating more frequent reapplication.
DEET is the most common repellent active ingredient, and its efficacy and toxicity have been the subject of numerous scientific studies. Most authorities recommend repellents containing DEET (N,N-diethylmetatoluamide) as the most reliable and long-lasting active ingredient. DEET repels mosquitoes, ticks, and other arthropods when applied to the skin or clothing. In general, the more DEET a repellent contains, the longer it can protect against mosquito bites. Low concentrations provide shorter-duration protection than higher concentrations; however, there appears to be no added benefit of concentrations of more than 50% DEET. A microencapsulated, sustained-release formulation can have a longer period of activity than liquid formulations at the same concentrations (6).
DEET has been so widely used that a great deal of testing has been done. Over the long history of DEET use, very few confirmed incidents of toxic reactions to DEET have occurred when the product is used properly. No definitive studies have been published about what concentration of DEET is safe for children. However, reports of serious illness in children after the use of DEET are extremely rare; DEET was used inappropriately in most of these cases. DEET formulations as high as 50% are recommended for both adults and children >2 months of age (7-9). The recommendations for DEET use in pregnant women do not differ from those for nonpregnant adults.
Repellents that do not contain DEET have not been tested as thoroughly as DEET-based products, although available data indicate that many offer a duration of protection from biting mosquitoes similar to that provided by similar concentrations of DEET. Used according to label instructions and reapplied as necessary, EPA-registered non-DEET repellents can provide acceptable protection from biting insects and are not expected to pose health risks to people, including children and other sensitive populations. Similar to DEET, summaries from EPA indicate that Picaridin is slightly toxic by eye, dermal and oral routes. PMD (p-menthane-3,8-diol) shows no adverse effects except for eye irritation. IR3535 has been used as an insect repellent in Europe for 20 years with no substantial adverse effects. Toxicity tests show that the IR3535 is not harmful when ingested, inhaled, or used on skin, although it may cause eye irritation if it enters a person’s eyes. Oil of citronella shows little or no toxicity, but may cause skin irritation.
Repellents applied according to label instructions may be used with sunscreen with no reduction in repellent activity (10). Products that combine sunscreen and repellent are not recommended, as sunscreen may need to be re-applied with greater frequency and in greater amounts than are needed to provide protection from biting insects.
Travelers should be advised to check the container to ensure that the product bears an EPA-approved label and registration number. The entire label should be read and the directions followed carefully. For example, if a tick repellent is needed, the product label should list this use. If ticks are not listed, the product may not be formulated for that use. Repellents should be stored away from children’s reach.
Travelers should be advised to use the following precautions when using repellents:
- Use enough repellent to cover exposed skin or clothing. Do not apply repellent to skin that is under clothing. Heavy application is not necessary to achieve protection.
- Do not apply repellent to cuts, wounds, or irritated skin.
- After returning indoors, wash treated skin with soap and water.
- Do not spray aerosol or pump products in enclosed areas; do not inhale the aerosol.
- Do not apply aerosol or pump products directly to the face. Spray hands and then rub them carefully over the face, avoiding eyes and mouth.
- When using repellent on a child, an adult should apply it to his or her own hands and then rub them on the child. Avoid the child’s eyes and mouth and apply sparingly around the ears.
- Do not apply repellent to children’s hands. (Children tend to put their hands in their mouths.)
- Do not allow children younger than 10 years old to apply insect repellent to themselves; an adult should do it for them. Keep repellents out of reach of children.
Protect infants younger than 2 months of age from biting mosquitoes by using an infant carrier draped with mosquito netting with an elastic edge for a tight fit.
Bed nets and repellents should be purchased before traveling and can be found in hardware, camping, sporting goods, and military surplus stores.
When purchasing repellents overseas, look for the EPA-registered active ingredients on the product labels. Permethrin or a similar insecticide, deltamethrin, may be purchased to treat bed nets and clothes.
