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Insect repellents crucial to deter spread of mosquito-borne viruses
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The rapidly changing epidemiology of Zika virus infection has raised concerns in many parts of the world, including the United States. Through a common vector, the Aedes mosquito, Zika adds to the danger already posed by other prominent tropical diseases currently endemic in the Western Hemisphere, such as chikungunya and dengue virus.
As of Aug. 10, in the United States alone, the CDC has reported 1,955 travel-associated cases and six locally acquired mosquito-borne Zika cases, with 22 of these cases transmitted sexually. Florida and New York comprise about 44% of all cases in the U.S.
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Presently, treatment for Zika infection is nonspecific and supportive, while prevention plays an important role in limiting the spread of infection. Prevention modalities include limiting travel to high-risk geographic areas, use of protective clothing, mosquito control efforts both outside and inside the home, and the application of effective topical insect repellents.
Regulation of insect repellent ingredients
Insect repellents commercially distributed and sold in the U.S. are required to be registered with the Environmental Protection Agency. This registration process entails provision of data documenting the safety (both to humans and the environment) and effectiveness of the specific insect repellent. Consumers can verify registration by the EPA registration number located on the product’s label.
The CDC and other medical organizations, including the AAP, recommend the use of EPA-registered insect repellent products for control of infectious diseases transmitted by insect vectors, such as Zika infection via Aedes mosquitoes.
A variety of insect repellent active ingredients are available in numerous products, although only several active ingredients are commonly recommended. The CDC and the AAP recommend DEET (N,N-diethyl-meta-toluamide), picaridin, IR3535, oil of lemon eucalyptus, or para-menthane-diol as active ingredients that function as effective insect repellents. Additional EPA-registered ingredients available in some products include citronella, 2-Undecanone and catnip oil.
The vast majority of commercially available products contain either DEET, oil of lemon eucalyptus, picaridin or IR3535. It is important to note that although many products containing these active ingredients are available, they differ widely by active ingredient concentration, which can significantly affect the duration of product efficacy.
Published literature reviews of insect repellent efficacy for Aedes mosquitoes mirror the recommendations described by the CDC and other medical organizations. DEET is commonly recommended, as it can provide long-lasting (8-12 hours or more, with higher concentrations) protection and is widely available in numerous products. A review published in Travel Medicine and Infectious Disease determined that DEET (20% concentration or greater) was the most efficacious insect repellent. Picaridin and oil of lemon eucalyptus also are widely available in many products and are effective.
In July, Consumer Reports evaluated insect repellent products, with three products containing DEET, picaridin, or oil of lemon eucalyptus, recommended as providing at least 7 hours of protection against Aedes mosquitoes (see table). Additional products tested were not recommended, even though some contained DEET or picaridin, as they did not provide long-lasting protection (ie, less than 2 hours).
A review of several hundred EPA-registered insect repellent products found manufacturer-reported durations of protection ranging up to 12 hours for DEET (34%). This information highlights the importance of not only selecting a product containing an active ingredient that is most likely to provide effective protection, but one that also contains a sufficient concentration of the active ingredient to provide a long duration of effectiveness.
Health concerns in children, pregnant women
Compared with other insect repellent active ingredients, DEET is used far more commonly in the U.S., and it has been estimated that 30% of the U.S. population uses DEET-containing products annually. The EPA labels DEET use without age restriction in children, stating that no data demonstrate a need for age restriction, nor demonstrate age-related adverse effects in young and mature animal studies.
DEET is classified by the EPA as having low acute toxicity; in addition, the EPA does not believe that specific DEET formulations or concentrations are safer for children. The EPA has assessed that DEET does not pose a health concern to the U.S. population, including children, when used properly by product-labeled instructions. The AAP, however, recommends restricting pediatric use of DEET to children aged 2 months and older, and to products containing no more than 30% DEET. Reasoning for these recommendations, however, is unclear.
As new information on the adverse fetal effects of Zika virus infection become more apparent, mosquito bite prevention strategies during pregnancy are becoming increasingly imperative. DEET is regarded as safe to use during pregnancy, and the CDC, the American Congress of Obstetricians and Gynecologists, and the AAP have endorsed its use.
In a blind, randomized controlled trial of 897 pregnant women (second and third trimesters), daily application of DEET was compared with a product carrier alone to assess the safety of DEET. No adverse effects on infant survival, growth, or development at birth, or at 1 year, were demonstrated. The CDC also regards products containing picaridin, IR3535, and oil of lemon eucalyptus as safe for use during pregnancy.
Usage of insect repellent products
Numerous insect repellent products containing the recommended active ingredients, in a variety of concentrations, are available, in addition to products only containing other active ingredients (eg, oil of soybean, castor oil, oil of citronella). As these other active ingredients have not been broadly recommended by professional medical organizations, they are best not used.
It is reasonable to initially use a product containing DEET, as it has a long history of safety and efficacy. The concentration of DEET in a product is important, as lower concentrations, while effective as an insect repellent, may provide only a relatively short duration of protection. Products containing at least 15% DEET should be used, as these products are more likely to provide 7 to 8 hours of protection per application.
Several DEET products are labeled to provide 11 to 12 hours of protection, and these products may be useful for children and adults spending considerable time outdoors, such as during hiking trips or organized camp activities. A practical disadvantage of DEET use includes its tendency to damage plastics, such as wristwatches or similar devices. If a natural insect repellent is desired, products containing oil of lemon eucalyptus can be recommended, although they are labeled for use only in persons aged 3 years and older.
Combination products containing an insect repellent and sunscreen are best avoided, as effective sunscreen use includes frequent reapplication (ie, every 2 hours), which is not appropriate for many insect repellent products. When using separate sunscreen and insect repellent products, sunscreen is best applied first, followed by insect repellent.
- References:
- Lupi E, et al. Travel Med Infect Dis. 2013; doi: 10.1016/j.tmaid.2013.10.005.
- McGready R., et al. Am J Trop Med Hyg. 2001;65:285-289.
- For more information:
- Edward A. Bell, PharmD, BCPS, is a professor of pharmacy practice at Drake University College of Pharmacy and Health Sciences and Blank Children’s Hospital and Clinics, Des Moines, Iowa. He also is a member of the Infectious Diseases in Children Editorial Board. Bell can be reached at ed.bell@drake.edu.
Disclosure: Bell reports no relevant financial disclosures.