JOURNAL OF THE LOUISIANA STATE MEDICAL SOCIETY
mosquito repellents for children six months to 12 years of age.¹⁴ The EWG recommends that pregnant women only use picaridin- containing repellents with 20 percent concentrations.¹²
nausea, and vomiting.¹⁹ According to the EPA, permethrin may be carcinogenic in humans if ingested based on studies in rats who developed tumors after chronic permethrin ingestion.¹⁹ In another study, a group of pregnant women used a 4% permethrin-containing product all over their bodies to treat scabies.²⁰ Another group of pregnant women used a 1% permethrin product to treat head lice.²⁰ These topically applied permethrin concentrations for ectoparasitic diseases did not affect the pregnancies in either group of pregnant women. Permethrin-containing insecticides are safe and effective when applied to clothing and not to exposed skin. The topical application of permethrin-containing insecticides is recommended only to treat scabies and head lice in children older than two months.²⁰ In all other cases, permethrin should be applied to clothing and other items, such as bed nets, hammocks, or sleeping bags, in order to be effective against mosquito bites.
IR3535 AND OIL OF LEMON EUCALYPTUS
While both DEET and picaridin are effective at repelling biting mosquitoes, IR3535may not be as effective as DEET inpreventing bites by Aedes species mosquitoes.³ Lupi et al. showed that 10% IR3535 formulations protected volunteers from mosquito bites.³ The durations of efficacy, however, were not statistically different.³ Oil of lemon eucalyptus, a plant-based repellent derived from Eucalyptus citriodora , is the least effectivemosquito repellent. Lupi and co-investigators demonstrated that oil of lemon eucalyptus repellents only protected against A. aegypti bites for 2-5 hours with 10% and 20% formulations respectively.³ ADVERSE EFFECTS OF IR3535 AND OIL OF LEMON EUCALYPTUS Both IR3535 and oil of lemon eucalyptus may cause skin and eye irritations.¹⁵ The manufacturers of oil of lemon eucalyptus- containing insect repellents have recommended not applying preparations to children under 3 years of age.¹⁵ The EWG only recommends IR3535 products containing 20% concentrations for pregnant women.¹²
DISCUSSION
In order to prevent mosquito bites, consumers should be aware of the differences between insect repellents and insecticides. As noted, repellents repel insects within centimeters of the skin surface, and insecticides kill insects on contact. Repellents are applied topically to the skin, and insecticides are applied to clothing and not skin, except in the treatment of head lice and scabies with permethrin. DEET, picaridin, IR3535, and oil of lemon eucalyptus are all insect repellents that are safe to apply to the skin using aerosols, lotions, pump sprays, and wipes. However, the insecticide, permethrin, should only be sprayed on personal items such as clothing, insect nets, sleeping bags, or boots for the best protection from mosquito bites. While lethal cases involving insect repellent exposures are rare, safety precautions should always be followed when applying insect repellents. The most serious adverse effects have occurred after massive ingestions and repeated heavy applications of insect repellents and pesticides, such as permethrin. In conclusion, DEET is themost studied and used insect repellent worldwide. At present, DEET is the best choice to prevent Aedes species mosquito bites and to prevent Zika virus disease. Picaridin fomulations appear to be effective alternatives for DEET, but have not been studied as extensively as DEET. Adverse effects from DEET and other insect repellents and insecticides may occur more often in children typically following ingestions or repeated heavy applications. The combination of topical 20- 30%DEET preparations, reapplied as necessary, and permethrin- impregnated clothing will offer the very best combination of repellents and insecticides to prevent Aedes species mosquito bites and the transmission of Zika virus disease.
PERMETHRIN
Permethrin is a synthetic pyrethroid-class insecticide derived from pyrethrin I, the active component of pyrethrum, an extract from dried Chrysanthemum cinerariaefolium flowers.¹⁶ Permethrin has low mammalian toxicity and does not accumulate in the environment.¹⁶ Eamsila et al. conducted a case-control study in soldiers in Colombia who wore permethrin-treated fatigues 24 hours per day for over four weeks.¹⁷ The soldiers who wore the permethrin- treated fatigues had a 3.5% incidence rate of malaria (three cases out of 86) versus a 14% malaria incidence rate in soldiers who wore untreated fatigues (12 cases out of 86).¹⁷ In a 1999 Afghan study, permethrin-impregnated headscarves provided significant protection from malaria.¹⁸ Investigators reported a 64% reduction in new cases in children up to 10 years old and a 38% reduction in new cases in all persons less than 20 years old.¹⁸ Permethrin-treated headscarves were not associated with a reduction in malaria incidence in persons over 20 years old.¹⁸
ADVERSE EFFECTS OF PERMETHRIN
Permethrin may cause irritation, itching, and burning if applied to mucous membranes or accidentally instilled in the eyes.¹⁹ If ingested, permethrin can cause sore throat, abdominal pain,
122 La State Med Soc VOL 170 JULY/AUG 2018
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