Protection against Mosquitoes and Other Arthropods

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 resistance and compliance with medication, and no similar preventive measures exist for other mosquito-borne diseases such as dengue. For many vector-borne diseases, no specific preventives are available.

General Preventive Measures

The principal approach to prevention of vector-borne diseases is avoidance. Tick- and mite-borne infections characteristically are diseases of “place;” whenever possible, known foci of disease transmission should be avoided. Although many vector-borne infections can be prevented by avoiding rural locations, certain mosquito- and midge-borne arboviral and parasitic infections are transmitted seasonally, and simple changes in itinerary can greatly reduce risk for acquiring them.

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 at dawn and dusk or in the evening. 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 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 (see the following section, “Repellents”) 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 comfort. Bed nets should be tucked under mattresses and can be sprayed with a repellent, such as permethrin. The permethrin will be effective for several months if the bed net is not washed. Aerosol insecticides can help clear rooms of mosquitoes.

Repellents

Travelers should be advised that permethrin-containing repellents (e.g., Permanone or deltamethrin) are recommended for use on clothing, shoes, bed nets, and camping gear. Permethrin is highly effective as an insecticide and as a repellent. Permethrin-treated clothing repels and kills ticks, mosquitoes, and other arthropods and retains this effect after repeated laundering. There appears to be little potential for toxicity from permethrin-treated clothing. The insecticide should be reapplied after every five washings.

Most authorities recommend repellents containing N,N-diethylmetatoluamide (DEET) as an 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 time it can protect against mosquito bites. However, there appears to be no added benefit of concentrations greater than 50%. A microencapsulated, sustained-release formulation can have a longer period of activity than liquid formulations at the same concentrations. Length of protection also varies with ambient temperature, amount of perspiration, any water exposure, abrasive removal, and other factors.

No definitive studies have been published about what concentration of DEET is safe for children. No serious illness has arisen from use of DEET according the manufacturer’s recommendations. DEET formulations as high as 50% are recommended for both adults and children >2 months of age. Lower concentrations are not as long lasting, offering short-term protection only and necessitating more frequent reapplication. Repellent products that do not contain DEET are not likely to offer the same degree of protection from mosquito bites as products containing DEET. Non-DEET repellents have not necessarily been as thoroughly studied as DEET and may not be safer for use on children. Parents should choose the type and concentration of repellent to be used by taking into account the amount of time that a child will be outdoors, exposure to mosquitoes, and the risk of mosquito-transmitted disease in the area. The recommendations for DEET use in pregnant women do not differ from those for nonpregnant adults.

DEET is toxic when ingested and may cause skin irritation in sensitive persons. High concentrations applied to skin can cause blistering. However, because DEET is so widely used, a great deal of testing has been done, and over the long history of DEET use, very few confirmed incidents of toxic reactions to DEET have occurred when the product is used properly.

Travelers should be advised that the possibility of adverse reactions to DEET will be minimized if they take the following precautions:

• 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. If repellent is applied to clothing, wash treated clothing before wearing again.
• 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 breathe in.
• Do not apply aerosol or pump products directly to the face. Spray your hands and then rub them carefully over the face, avoiding eyes and mouth.
• When using repellent on a child, apply it to your own hands and then rub them on your 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 under ten years old to apply insect repellent to themselves; have an adult do it for them. Keep repellents out of reach of children.
• Protect infants two months of age and under by using a carrier draped with mosquito netting with an elastic edge for a tight fit.
• Bed nets, repellents containing DEET, and permethrin should be purchased before traveling and can be found in hardware, camping, sporting goods, and military surplus stores. Overseas, permethrin or another insecticide, deltamethrin, may be purchased to treat bed nets and clothes.

— Paul Arguin, Ann Barber, Meghna Desai, Roger Nasci, Monica Parise, Robert Wirtz