It’s Summer— and about to be humid and hot, an environment uniquely favorable to the exponential growth and survival of disease-transmitting mosquitos. West Nile Virus, one of the better known arboviruses, is an illness transmitted via a pesky insect to a human host. In comparison, a zoonotic virus is transmitted via an animal to a human- a well-known example of this type of disease is the Ebola virus.

In the vast majority of West Nile cases, upwards of 80%, people infected will be completely asymptomatic. Approximately 20% will develop a mild to moderate illness consisting of fever and body aches predominately, reminiscent of the seasonal flu. Less than 1% of infected persons will actually develop West Nile Encephalitis (WNE) – the much feared but quite rare neurologic progression associated with the virus. So, who in particular is at risk of developing WNE? The elderly mainly – likely because of reduced immune system function that makes this population more at risk for disease in general – cancer, shingles etc. Furthermore, in a community with a substantial mosquito population, the odds that you and your children have already been infected with West Nile go up, and once infected, it is extremely unusual to become infected again. Immunity DOES result from infection to West Nile. That being said, if you live in a hot, humid environment like ours, there is a good chance you have already been infected with West Nile! In Texas alone, by the end of last summer, only 8 cases of neuroinvasive disease had been reported with no associated deaths. If you consider that less than 1% of affected persons will progress to WNE and even a smaller number of children will follow this course, the odds are definitely on our side that we have seen this illness already and mounted an antibody response to it! That being said, protection still makes sense as long as our protective efforts avoid over-application of repellents and potential resultant toxicity!

DEET, N,N-Diethyl-meta-toluamide, is a commonly used repellent because it is highly effective at deterring mosquitos. The AAP supports the use of DEET as protection against West Nile Virus, but recommends that low insecticide concentrations be applied to children’s skin, and preferably not to infants less than 6 months of age. But, how much DEET is absorbed through the skin and into the systemic circulation. How quickly do we excrete the active ingredient and its metabolites? What are the potential side effects?

Approximately 5-18% of DEET is pulled past the epidermis, or top layer of skin, and moved into the systemic circulation. Of note, DEET compounded into an alcohol base makes the product even more penetrable. The body metabolizes DEET quickly via the liver and excretes the metabolites in urine usually within 12 hours. Unfortunately, because of limited human studies, we are not entirely sure how much unmetabolized product is stored in tissues, and any eventual effects tissue storage might cause. We do know that “excessive” use, especially among military and forest service personnel, who require higher concentrations of DEET on essentially a daily basis for protection, have experienced more severe adverse effects due to this chronic exposure. Reported effects included insomnia, muscle cramps, mood disturbances and rashes. In addition, application of DEET to large areas of the body over a period of days to weeks, predominately in children, has led to seizures, bradycardia, nausea, vomiting, blistering skin eruptions, lethargy, ataxia (uncoordinated spastic movements), encephalopathy (brain swelling) and anaphylaxis. Neurotoxicity is the most commonly reported systemic toxic effect of DEET and the mechanism for how this occurs is largely unknown. It has been theorized that DEET may cause brain cells to break apart and/or DEET may compromise the integrity of the blood-brain barrier so that normal brain insulation is lost. Clearly, DEET is a repellent to use sparingly…

Like all things, there is risk and argument in either extreme approach. Avoiding repellent completely will make you and your children more at risk for contracting West Nile, but excessive repellent administration is not a safe tactic either.

There is a grey method, as always—

  1. Cutter, OFF Family Care and Avon SkinSoSoft use the repellent Picaridin in their products. This ingredient, which is similar to black pepper, is minutely absorbed by the skin of humans and rapidly excreted in urine. Even in lab rats that absorb over 60% of the pesticide through their porous skin (compared to our ~5% absorption), almost all the absorbed picaridin is secreted within 24 hours into urine, and because the active ingredient mirrors a food, our bodies are more apt to recognize, metabolize and excrete this repellent without negative secondary effects.
  2. Any brand Picaridin wipes – such as Natrapel – the repellent is delivered via a towellette instead of a spray, thereby inhalation of the chemical is a non-issue and focus can be given to exposed areas while effectively avoiding hands – which often end up in the mouth!
  3. BiteBlocker is a natural repellent that uses mainly food grade ingredients, such as coconut oil and vanilla and is deemed safe by the AAP for use in little ones. Not as effective as Picaridin containing sprays, but very safe.
  4. EcoSmart repellent is a peppermint oil base so it smells good! Strangely, a potential side effect of peppermint oil is heartburn but a frequent benefit is improved upset stomach. Worth a try!
  5. Regardless of which repellent you opt for:
    1. Only apply to exposed skin and clothes, not to skin under clothes!
    2. Kids should shower or bathe at the end of the day if repellent and sunscreens have been applied that day.
    3. Avoid being outside during the times of day when mosquitos are most active, namely dusk.
  6. Lastly, it never hurts to actively support immune system function as a means of avoiding symptomatic West Nile – probiotics, raw/minimally processed nutrition, adequate sleep and frequent exercise all contribute to our ability to fight illness in general.

But of course, it’s Summer, and the importance of the snowcone can’t be underestimated either! 🙂

Osimitz TG & Murphy JV, Neurological effects associated with use of the insect repellent N, N-diethyl-m-toluamide (DEET). J Toxicol Clin Toxicol 1997;35:435-441.

Sudakin DL, Trevathan WR, DEET: A Review and Update of Safety and Risk in the General Population. J Toxicol Clin Toxicol 2003;41:831-839