Mosquitoes, Ticks & Other Arthropods

CDC Yellow Book 2024

Environmental Hazards & Risks

Author(s): John-Paul Mutebi, John Gimnig

Vectorborne diseases are found at almost every travel destination. Because few vaccines are available to protect travelers, the best way to prevent vectorborne diseases is to avoid being bitten by ticks and insects, including mosquitoes, fleas, chiggers, and flies, that transmit pathogens that cause disease. Travel health practitioners should advise travelers to use repellents and take other precautions to prevent bites.

Vaccine Options & Malaria Prophylaxis

Vaccines are currently available to protect against 3 vectorborne diseases in US travelers: Japanese encephalitis, tick-borne encephalitis, and yellow fever (see the respective chapters in Section 5 for details). No vaccines or prophylactic drugs are available in the United States for other mosquito-borne diseases (e.g., chikungunya, filariasis, West Nile encephalitis, Zika); tick-borne diseases (e.g., Lyme borreliosis, relapsing fever); sand fly–borne diseases (e.g., cutaneous or visceral leishmaniasis); or blackfly–borne diseases (e.g., onchocerciasis [river blindness]).

In June 2021, Dengvaxia was recommended by the Advisory Committee on Immunization Practices (ACIP) to prevent dengue in children aged 9–16 years who had laboratory-confirmed previous dengue virus infection and who live in dengue-endemic areas. Dengue is endemic to the US territories of American Samoa, Puerto Rico, and US Virgin Islands, and to freely associated states including the Federated States of Micronesia, the Republic of Marshall Islands, and the Republic of Palau. The dengue vaccine will not be available for use in travelers not living in dengue-endemic areas in the US territories, however.

Prophylactic drugs are available to protect against malaria; however, the effectiveness of malaria prophylaxis is variable, depending on patterns of drug resistance, bioavailability, individual behavior, and compliance with medication (see Sec. 2, Ch. 5, Yellow Fever Vaccine & Malaria Prevention Information, by Country, and Malaria Information by Country).

Insect Repellents

When used as directed, insect repellents registered by the Environmental Protection Agency (EPA) have been proven safe and effective, even for pregnant and breastfeeding people. The Centers for Disease Control and Prevention (CDC) has evaluated information published in peer-reviewed scientific literature and data available from EPA to identify several types of EPA-registered products that safely and effectively prevent insect bites. 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 United States; 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. CDC does not recommend using “pure” oil of lemon eucalyptus (an essential oil that is not formulated) as a repellent, because it has not undergone validated testing for safety and efficacy and is not registered with EPA as an insect repellent. In general, parents should not use products containing OLE or PMD on children <3 years old to avoid potential allergic skin reactions.

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. The biopesticide repellents (OLE, PMD, IR3535, and 2-undecanone) are derived from, or are synthetic versions of, natural materials.

Travelers can find the right insect repellent for their needs by searching the EPA website Find the Repellent that is Right for You and the National Pesticide Information Center website, Choosing and Using Insect Repellents. Recommendations from these websites are based on peer-reviewed journal articles and scientific studies and data submitted to regulatory agencies.

Ideally, travelers should purchase repellents before departing the United States. A wide variety of repellents are available at camping, sporting goods, and military surplus stores. When purchasing repellents overseas, travelers should look for the active ingredients specified above on the product labels; some names of products available internationally also are provided above.


Published data indicate that repellent efficacy and duration of protection vary considerably among products and among arthropod species. Product efficacy and duration of protection are also markedly affected by ambient temperature, level of activity, amount of perspiration, exposure to water, being rubbed off during activities, and other factors.

In general, higher concentrations of active ingredients provide longer duration of protection, regardless of the active ingredient. Products with <10% active ingredient might offer only limited protection, often 1–2 hours. Products that offer sustained-release or controlled-release (microencapsulated) formulations, even with lower active ingredient concentrations, might provide longer protection times. Studies suggest that DEET efficacy tends to peak at a concentration of ≈50%, and that concentrations above that do not offer a marked increase in protection time against mosquitoes. Regardless of the product used, if travelers start getting bitten they should reapply, but not more often than the label allows.

The effectiveness of non–EPA-registered insect repellents, including some natural repellents, is unknown, and travelers should avoid using them (see EPA webpage on Using Insect Repellents Safely and Effectively with Children).

Repellents & Sunscreen

Repellents applied according to label instructions can be used with sunscreen with no reduction in repellent activity. However, limited data show that DEET-containing insect repellents applied over sunscreen decrease the sun protection factor (SPF) of the sunscreen by one-third.

Travelers should avoid products that combine sunscreen with repellents because sunscreen might need to be reapplied more often and in larger amounts than what is needed for the repellent component to provide protection from biting insects. In general, travelers should use separate products, apply sunscreen first, and then apply the repellent. Because SPF decreases when a DEET-containing insect repellent is used, travelers might need to reapply sunscreen more frequently. Travelers must remember to use both sunscreen and insect repellents according to the manufacturer’s instructions for each.

Use on Clothing & Gear

Travelers can treat clothing, hats, shoes, mosquito nets, outwear, and camping gear with permethrin for added protection. Permethrin is a highly effective insecticide, acaricide (pesticide that kills ticks and mites), and repellent. At a concentration of 0.5%, 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 before packing for travel to allow them to dry. As with all pesticides, travelers should always follow the label instructions.

Products such as Permanone and Sawyer, Permethrin, Repel, and Ultrathon Permethrin Clothing Treatment are registered with the EPA specifically for use by consumers to treat clothing and gear. Alternatively, clothing pretreated with permethrin is commercially available and marketed to consumers in the United States as Insect Shield, BugsAway, or Insect Blocker.

Permethrin-treated materials retain repellency or insecticidal activity after repeated launderings, but should be retreated as described on the product label to provide continued protection. Clothing treated before purchase is labeled for efficacy through many launderings. Clothing treated with the other repellent products described above (e.g., DEET) provides protection from biting arthropods but will not last through washing and will require more frequent application.


Box 4-09 contains precautions clinicians can share with travelers regarding the use of insect repellents. Severe reactions to insect repellents are rare. If a traveler experiences a rash or other reaction (e.g., itching, swelling) from a repellent, they should wash off the product using mild soap and water and discontinue its use. Travelers seeking health care because of a reaction to a repellent should take the product container with them to the doctor’s office. Reactions associated with insect repellent use are outlined in MedlinePlus.

Permethrin should never be applied to the skin but only to clothing, mosquito nets, or other fabrics as directed on the product label.


Box 4-09 Precautions when using insect repellents: guidance for travelers

  • Apply repellents only to exposed skin or clothing, as directed on the product label. Do not apply to skin covered by clothing.
  • Never use repellents on cuts, wounds, or irritated skin.
  • When using sprays, do not spray directly on the face—spray product on hands first and then apply to face. Do not apply to eyes or mouth; apply only sparingly around ears.
  • Wash hands after application to avoid accidental ingestion or exposure to eyes.
  • Children should not handle repellents. Instead, adults should apply repellent to their own hands first and then gently spread product on the child’s exposed skin. Avoid applying repellents 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 repellent 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.
  • Follow instructions on the product label for handling repellent-treated clothing.

Children & Pregnant People

Certain insect repellent products containing OLE as their sole active ingredient at concentrations of ≤30% can be used on children <3 years of age; parents should always read the product label before use. Insect repellents containing DEET, Picaridin, IR3535, and 2-undecanone can be used on children without age restriction (see EPA webpage on Using Insect Repellents Safely and Effectively with Children). Travelers can protect infants from insect bites by dressing them in clothing that covers their arms and legs, by covering strollers and baby carriers with mosquito netting, and by using appropriate insect repellent. Other than the safety tips listed above, EPA does not recommend any additional precautions for using registered repellents on children or on people who are pregnant or lactating.

Insect Bite Prevention

Travelers can reduce their risk for bites from mosquitoes, ticks, fleas, sand flies, and other arthropods by using EPA-registered insect repellents. Travelers should also 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 also might help reduce risk. Application of repellents or insecticides (e.g., 0.5% permethrin) to clothing and gear can provide an added layer of protection. Remind travelers to always follow instructions on the label when applying repellents or insecticides. Additional prevention techniques are provided below.


More than 3,000 different mosquito species live worldwide, and each has specific biting behaviors; some species have local and regional variations, meaning biting behaviors might not be uniform throughout the distribution range of a specific species. Mosquitoes bite throughout the day and night, although each species tends to have peak activity at certain times.

The peak biting activity of Aedes aegypti (the primary vector for chikungunya, dengue, Mayaro, yellow fever, and Zika) is after sunrise (dawn) and at sunset (dusk). By contrast, peak biting activity for Culex quinquefasciatus (a vector for filariasis; Japanese, St. Louis, and West Nile encephalitis; and Usutu) is typically after sunset, usually between 10–11 p.m. The biting activity of Anopheles mosquitoes, the primary vectors for malaria worldwide, varies with the species. Peak biting activity for Anopheles gambiae, for example, the primary malaria vector in Africa, is between 3–6 a.m. Peak biting activity for Anopheles albimanus, an important malaria vector in Central and South America, is between 10–11 p.m.

Avoiding peak biting activity periods minimizes the chances of vectorborne disease. Although some mosquito species can roughly be described as day-biters and others as nocturnal feeders, regional variations and overlap in feeding times means that travelers need to be cautious about mosquito bites at all times of day and night in regions where mosquito-borne diseases are a risk.

As much as possible, travelers should avoid visiting areas with active outbreaks of mosquito-borne diseases. The CDC Travelers’ Health website provides updates on regional disease transmission patterns and outbreaks. For more on mosquito bite prevention techniques, see Prevent Mosquito Bites.

Spatial Repellents

Spatial repellents, including aerosol insecticide sprays, vaporizing mats, and mosquito coils, contain active ingredients (e.g., metofluthrin, allethrin) people can use to protect against insect bites. Spray aerosols can help clear mosquitoes from larger spaces, while coils and spatial repellents repel mosquitoes from more circumscribed areas.

Although many of these products have repellent or insecticidal activity under certain conditions, they have not yet been adequately evaluated in peer-reviewed studies for efficacy in preventing vectorborne diseases. Travelers should supplement use of these products with an EPA-registered repellent on skin or clothing and by using mosquito nets in areas where vectorborne diseases are a risk or biting arthropods are noted.

Some products available internationally might contain pesticides that are not registered for use in the United States. Conversely, travelers intending to bring their own spatial repellents should make sure the repellents are legal for use at their destination. Travelers should consult the US embassy website in the destination country. Advise travelers to use spatial repellents with caution and to avoid direct inhalation of spray or smoke.


Hiking, camping, and hunting are examples of activities that could bring travelers in close contact with ticks. Travelers should avoid wooded and brushy areas with high grass and leaf litter, and stay in the center of hiking trails. For more on tick bite prevention techniques, see Preventing Tick Bites.

Figure 4-01 provides instructions on how to remove attached ticks. Counsel travelers who develop rash or fever within several weeks of removing a tick to see a doctor; travelers should provide details (if known) about the bite, including when and where it occurred.

Figure 4-01 How to remove a tick: instructions for travelers

Figure 4-01 How to remove a tick: instructions for travelers

View Larger Figure

If a tick is attached to the skin, remove it as soon as possible.

Several tick removal devices are available on the market, but a plain set of fine-tipped tweezers work very well.
Using fine-tipped tweezers, grasp the tick as close to the surface of the skin as possible.

Pull upward with steady, even pressure without twisting or jerking the tick; twisting or jerking can cause the mouthparts of the tick to break off in the skin.

If the mouthparts of the tick break off in the skin, and they can be removed easily, remove them with tweezers.
If the mouthparts cannot be removed easily, leave them alone and allow the skin to heal.

After removing the tick, thoroughly clean the bite area and your hands with rubbing alcohol or soap and water.
Never crush a tick with your fingers.

Dispose of live ticks by placing them in alcohol or a sealed bag/container, wrapping them tightly with tape, or flushing them down the toilet.


Flea bites often occur on the lower legs and feet. Travelers can protect these areas of the body by wearing long socks and pants. In addition, travelers should not feed or pet stray or wild animals. For more on flea bite prevention techniques, see Preventing Flea Bites. For more on the importance of avoiding animals while traveling, see Sec. 4, Ch. 7, Zoonotic Exposures: Bites, Stings, Scratches & Other Hazards.

Sand Flies

Sand flies are most active during dawn and dusk. If possible, travelers should limit outdoor activities during those times.

Bed Bugs

Bed bugs have not been shown to transmit disease to humans. A recent surge in bed bug infestations worldwide, particularly in high-income countries, is thought to be related to international travel, changes in pest control strategies in travel lodgings, and insecticide resistance. Bed bug infestations have been reported in hotels, theaters, and locations where people congregate, even in the workplace, dormitories, and schools.

Bed bugs are small, flat insects that are reddish-brown in color, wingless, and range from 1–7 mm in length. Bed bug bites can produce strong allergic reactions and considerable emotional stress. Bed bugs can be transported in luggage and on clothing and by transporting personal belongings in contaminated transport vehicles.

Travelers can take measures to avoid bed bug bites and avoid transporting them in luggage and clothing (Box 4-10). Prevention is by far the most effective and inexpensive way to protect oneself from these pests. The cost associated with ridding a personal residence of bed bugs is considerable, and efforts at controlling bed bugs are often not immediately successful, even when conducted by professionals.

Box 4-10 Recommended protective measures to avoid or reduce bed bug exposure


Look carefully 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. Bed bug eggs and nymphs are very small and can be easily overlooked.


Travelers who observe evidence of bed bug activity—whether it be the bugs themselves or physical signs (e.g., blood-spotting on linens)—should seek alternative lodging.


Keep suitcases off the floor. Keep suitcases closed when not in use. Remove clothing and needed items (e.g., toiletry bags and shaving kits) from the suitcase only as necessary. Carefully inspect all clothing and other items before returning them to the suitcase.

The following authors contributed to the previous version of this chapter: John-Paul Mutebi, John E. Gimnig

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