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Chapter 3 Environmental Hazards & Other Noninfectious Health Risks

Mosquitoes, Ticks & Other Arthropods

John-Paul Mutebi, John E. Gimnig

Because vector control programs vary in coverage and effectiveness, travel health practitioners should advise travelers to use repellents and other general protective measures against biting arthropods. Although prophylactic drugs are available to protect against malaria, the effectiveness is variable depending on patterns of drug resistance, bioavailability, and compliance with medication. And while vaccines are available for diseases such as yellow fever and Japanese encephalitis, there are no available vaccines or chemoprophylaxis for other mosquitoborne diseases such as dengue, chikungunya, Zika, filariasis, and West Nile encephalitis; for tickborne diseases such as Lyme borreliosis, tickborne encephalitis, and relapsing fever; for sand fly–borne diseases such as visceral and cutaneous leishmaniasis; and for black fly–borne diseases such as onchocerciasis (river blindness).

The Environmental Protection Agency (EPA) regulates repellent products in the United States. CDC recommends that consumers use only those repellent products registered by the EPA. Registration indicates that the EPA has determined that the product is both efficacious and safe for human use, when applied according to the instructions on the label.

GENERAL PROTECTIVE MEASURES

Avoid outbreaks. As much as possible, travelers should avoid known foci of epidemic arthropodborne disease transmission. The CDC Travelers’ Health website provides updates on regional disease transmission patterns and outbreaks (www.cdc.gov/travel).

Wear appropriate clothing. Travelers can minimize areas of exposed skin by wearing long-sleeved shirts, long pants, boots, and hats. Tucking in shirts, tucking pants into socks, and wearing closed shoes instead of sandals may help reduce risk. Application of repellents or insecticides, such as permethrin, to clothing and gear can provide an added layer of protection. Remind travelers to always follow instructions on the label when applying repellents to clothing. (Additional information on clothing repellents and their proper use is included below.)

Check for ticks. Travelers should inspect themselves and their clothing for ticks during outdoor activity and at the end of the day. Prompt removal of attached ticks can prevent some infections. Showering soon after leaving a tick-infested area may prevent ticks from attaching or facilitate detection of recently attached ticks.

Bed nets. Bed nets provide essential protection to travelers staying in accommodations lacking adequate window screens and air conditioning. Bed nets that do not reach the floor should be tucked under mattresses. Treating bed nets with a pyrethroid insecticide helps maximize their efficacy. Travelers may opt to buy a pretreated net or, as an alternative, apply the insecticide after purchase. Nets treated with a pyrethroid insecticide will be effective for several months if not washed. Long-lasting pretreated nets may be effective for much longer.

Insecticides and spatial repellents. Active ingredients in these products, metofluthrin and allethrin, provide protection from mosquito bites over a wide area. Spray aerosols can clear rooms or areas of mosquitoes; coils, vaporizing mats, and spatial repellents repel mosquitoes from a circumscribed area. Use insecticides and repellent products with caution, avoiding direct inhalation of spray or smoke.

Although many of these products demonstrate insecticidal or repellent activity under particular conditions, their efficacy in preventing vectorborne disease has not been evaluated adequately in peer-reviewed studies. For this reason, reliance on these products alone may afford insufficient protection from bites. Encourage travelers to apply an EPA-registered repellent to their skin and/or clothing and to use bed nets wherever vectorborne diseases are a risk.

Optimum protection can be provided by applying the repellents described in the following sections to clothing and to exposedskin (Box 3-01).

REPELLENTS FOR USE ON SKIN AND CLOTHING

CDC has evaluated information published in peer-reviewed scientific literature and data available from EPA to identify several types of EPA-registered products that provide repellent activity sufficient to help people reduce the bites of disease-carrying insects. Products containing the following active ingredients typically provide reasonably long-lasting protection:

  • DEET (chemical name: N,N-diethyl-m-toluamide or N,N-diethyl-3-methyl-benzamide). . Products containing DEET include, but are not limited to, Off!, Cutter, Sawyer, and Ultrathon.
  • Picaridin (KBR 3023 [Bayrepel] and icaridin outside the US; chemical name: 2-(2-hydroxyethyl)-1-piperidinecarboxylic acid 1-methylpropyl ester). Products containing picaridin include, but are not limited to, Cutter Advanced, Skin So Soft Bug Guard Plus, and Autan (outside the United States).
  • Oil of lemon eucalyptus (OLE) or PMD (chemical name: para-menthane-3,8-diol), the synthesized version of OLE. Products containing OLE and PMD include, but are not limited to, Repel and Off! Botanicals. This recommendation refers to EPA-registered products containing the active ingredient OLE (or PMD). CDC does not recommend using “pure” oil of lemon eucalyptus (essential oil not formulated) as a repellent. It has not undergone similar, validated testing for safety and efficacy and is not registered with EPA as an insect repellent.
  • IR3535 (chemical name: 3-[N-butyl-N-acetyl]-aminopropionic acid, ethyl ester). Products containing IR3535 include, but are not limited to, Skin So Soft Bug Guard Plus Expedition and SkinSmart.
  • 2-undecanone (chemical name: methyl nonyl ketone). The product BioUD contains 2-undecanone.

EPA characterizes the active ingredients DEET and picaridin as “conventional” repellents. Biopesticide repellents—OLE, PMD, IR3535, and 2-undecanone—are derived from, or are synthetic versions of, natural materials.

Repellent Efficacy

Published data indicate that repellent efficacy and duration of protection vary considerably among products and among mosquito and tick species. Ambient temperature, level of activity, perspiration, water exposure, abrasive removal, and other factors affect efficacy and duration of protection. In general, higher concentrations of active ingredients provide longer duration of protection, regardless of the active ingredient. Products with <10% active ingredient may offer only limited protection, often 1–2 hours. Products that offer sustained-release or controlled-release (microencapsulated) formulations, even with lower active ingredient concentrations, may provide longer protection times. Studies suggest that concentrations of DEET above approximately 50% do not offer a marked increase in protection time against mosquitoes; DEET efficacy tends to plateau at a concentration of approximately 50%. CDC recommends using products with ≥20% DEET on exposed skin to reduce biting by insects that may spread disease.

Recommendations regarding use of repellents are based on peer-reviewed scientific studies and data submitted to regulatory agencies. People may experience some variation in protection from different products. Regardless of the product used, travelers getting insect bites should reapply the repellent according to the label instructions, try a different product, or, if possible, leave the area.

Ideally, travelers should purchase repellents before traveling. They are sold online as well as in hardware stores, drug stores, supermarkets, camping, sporting goods, and military surplus stores. When purchasing repellents overseas, look for the active ingredients specified above on the product labels.

Repellency Awareness Graphic

A new graphic appearing on the label of insect repellents applied to the skin helps consumers more easily identify for how long the repellent is effective against mosquitoes and ticks (Figure 3-02). Use of this graphic by manufacturers is voluntary. Companies that apply to the EPA for permission to use the graphic must first provide data documenting their current testing protocols and standard evaluation practices.

Box 3-01. Maximizing protection from mosquitoes and ticks

To optimize protection against mosquitoes and tick bites:

  • Wear a long-sleeved shirt, long pants, and socks.
  • Treat clothing with permethrin or purchase pretreated clothing.
    • Permethrin-treated clothing will retain repellent activity through multiple washes.
    • Repellents used on skin can also be applied to clothing but provide shorter duration of protection (same duration as on skin) and must be reapplied after laundering.
  • Apply lotion, liquid, or spray repellent to exposed skin.
  • Use repellent whenever outdoors (or indoors if mosquitoes can get inside); mosquitoes can bite any time of day or night.
  • Check yourself during and after outdoor activity (your entire body); remove any attached ticks promptly.

Figure 3-02. Sample repellency awareness graphic for skin-applied insect repellents1

Figure 3-02. Sample repellency awareness graphic for skin- applied insect repellents

View Larger Figure

Repellents and Sunscreen

Combined sunscreen/repellents are not recommended. Advise travelers to use separate products, applying sunscreen first, followed by repellent. Repellents applied according to label instructions may be used with sunscreen with no reduction in repellent activity. Limited data show that DEET-containing insect repellents applied over sunscreen decrease the sun protection factor of the sunscreen by one-third; travelers using both products may therefore need to reapply sunscreen more frequently. In general, travelers typically need to apply sun protection more often and in larger amounts than they do insect repellent.

Repellents and Insecticides for Use on Clothing

Travelers can apply permethrin to clothing, hats, shoes, bed nets, jackets, and camping gear for added protection. Products such as Permanone and Sawyer, Permethrin, Repel, and Ultrathon Permethrin Clothing Treatment are EPA-registered specifically to treat clothing and gear. Alternatively, commercially available clothing pretreated with permethrin is marketed to consumers in the United States as Insect Shield, BugsAway, or Insect Blocker.

Permethrin is a highly effective insecticide, acaricide (pesticide that kills ticks and mites), and repellent. Permethrin-treated clothing repels and kills ticks, chiggers, mosquitoes, and other biting and nuisance arthropods. Clothing and other items must be treated 24–48 hours in advance of travel to allow them to dry. As with all pesticides, follow the label instructions when using permethrin clothing treatments.

Permethrin-treated materials retain their ability to repel or kill insects after repeated launderings. To provide continued protection, travelers should retreat their clothing and gear as described on the product label. Clothing treated before purchase is labeled for efficacy through 70 launderings. Clothing treated with the other repellent products described above (such as DEET) provides protection from biting arthropods but will not last through washing and will require more frequent application.

Precautions when Using Insect Repellents

Instruct travelers to take the following precau­tions when using repellents:

  • Apply only to exposed skin or clothing, as directed on the product label. Do not apply to skin covered by clothing.
  • Never use on cuts, wounds, or irritated skin.
  • When using sprays, do not spray directly on face—spray on hands first and then apply to face. Do not apply to eyes or mouth, and only sparingly around ears.
  • Wash hands after application to avoid accidental exposure to eyes or ingestion.
  • Children should not handle repellents. Instead, adults should apply to their own hands first and then gently spread on the child’s exposed skin. Avoid applying directly to children’s hands. After returning indoors, wash children’s treated skin and clothing with soap and water or give the child a bath.
  • Use just enough to cover exposed skin or clothing. Heavy application and saturation are generally unnecessary for effectiveness. If biting insects do not respond to a thin film of repellent, apply a bit more.
  • After returning indoors, wash repellent-treated skin with soap and water, or bathe. Wash treated clothing before wearing it again. This precaution may vary with different products—be sure to check the label.

If travelers experience a rash or other reaction (itching or swelling) from an insect repellent, they should wash off the product using mild soap and water and discontinue its use. For severe reactions, call a local poison-control center for further guidance. Travelers seeking health care because of a reaction to a repellent should bring the product container with them to show the doctor. Never apply permethrin to skin but only to clothing, bed nets, or other fabrics as directed on the product label.

Children and Pregnant Women

Most repellents can be used on children aged >2 months. Protect infants aged <2 months from mosquitoes by using an infant carrier draped with mosquito netting with an elastic edge for a tight fit. Products containing OLE specify that they should not be used on children aged <3 years. Other than the safety tips listed above, EPA does not recommend any additional precautions for using registered repellents on children or on pregnant or lactating women.

USEFUL LINKS

BED BUGS

The recent resurgence in bed bug infestations worldwide, particularly in developed countries, is giving travelers cause for concern. Although bed bugs do not transmit diseases, their bites may be a nuisance. Travelers can take measures to avoid bed bug bites and avoid transporting them in luggage and clothing (Box 3-02).

Box 3-02. Bed bugs and international travel

Bed bugs are small, flat insects that are reddish-brown in color, wingless, and range from 1 to 7 mm in length. Although bed bugs have not been shown to transmit disease, their bites can produce strong allergic reactions and considerable emotional stress.

A recent resurgence in bed bug infestations worldwide, particularly in developed countries, is thought to be related to the increase in international travel, pest control strategy changes in travel lodgings, and insecticide resistance. Bed bug infestations have been reported increasingly in hotels, theaters, and any locations where people congregate, including the workplace, dormitories, and schools. Travelers may transport bed bugs in luggage and on clothing. Personal belongings transported in vehicles infested with bed bugs is another means of spreading these insects.

PROTECTIVE MEASURES AGAINST BED BUGS

Encourage travelers to take the following precautions to avoid or reduce their exposure to bed bugs:

  • Inspect the premises of hotels or other sleeping locations for bed bugs on mattresses, box springs, bedding, and furniture, particularly built-in furniture with the bed, desk, and closets as a continuous structural unit. Travelers who observe evidence of bed bug activity—whether it is the bugs themselves or physical signs such as blood-spotting on linens—should seek alternative lodging.
  • Keep suitcases closed when they are not in use and keep them off the floor.
  • Remove clothing and personal items (such as toiletry bags and shaving kits) from the suitcase only when they are in use.
  • Carefully inspect clothing and personal items before returning them to the suitcase.
  • Keep in mind that bed bug eggs and nymphs are very small and can be overlooked easily.

Prevention is by far the most effective and inexpensive way to protect oneself from these pests. The cost of ridding a personal residence of these insects is considerable, and efforts at control are often not immediately successful even when conducted by professionals.

BIBLIOGRAPHY

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