Scientists from Belgium and Cambodia have recently found that topical mosquito repellent efficacy is relatively poor when it comes to reducing the incidence of malaria. The results for the trial, funded by The Bill and Melinda Gates Foundation, were published in the medical journal, The Lancet on June 30, 2016.

The reason behind this failure to prevent community level malarial disease was seen to be human behavior. The researchers observed that despite being freely available, only 8% of the people actually used these topical repellents in contrast with the fact that 70% of the people in the trial reported its regular use.

This trial is the most comprehensive and largest effort till date, where efficacy of use of topical repellents as an additional measure to control malaria along with regular long-lasting insecticidal nets (LLINs) was seen.

25,000 participants in both study and control groups, were given (picaridin) SC Johnson mosquito repellant and a placebo respectively along with insecticidal nets to observe if any additional protection occurred at the communal level.

After this cluster randomized trial, scientists concluded that mass distribution of a prevention tool may not necessarily translate into communal protective efficacy due to human nature.

Sarah Jane Moore, a researcher from Swiss Tropical and Public Health Institute in Switzerland wrote in an analysis piece on the study for The Lancet, “Topical repellents are an imperfect vector control tool simply because they must be used frequently, inevitably resulting in inconsistent compliance and incorrect application.”

User compliance is an important factor when considering implementation of large-scale interventions for disease prevention and control. Previously it has been seen that even trained personnel like soldiers do not apply the repellent if they do not perceive insect bites as a disease risk.

Low use of insect repellents has been seen in multiple instances primarily due to its irritating smell, forgetfulness, non-availability, and perceived side effects.

Overall, new cases of Zika in the United States have resulted in a total of 99 million units of insect repellents being sold in the last year, according to a Chicago-based market research company. The new sales accounted for a boost of 648% from last year.

The company, SC Johnson, the largest insect repellant manufacturer in the world, has amped up both its production capability and the price of its products. The recorded average price per unit for the company this year was $6.35, up $0.19  from the previous year.

Jeff McCollum, SC Johnson Public Affair Manager, says that demand in United States was 50% higher than in 2015. In regions like Latin America and Brazil the demand is three times what it was in last year.

SC Johnson sold 13.7 million units of Off Outdoor Insect Repellent in 52 weeks last year which was a 334% increase in sales. India, which has high prevalence of malaria, also saw 44,000 million retail sales of insect repellents alone in the last year.

Researchers led by Dr Sluydts however made one interesting discovery – the individual efficacy of picaridin repellant was seen to be quite high and in line with previous clinical reports. This was true even when additional communal protection by the repellents was nearly nonexistent when compared to protection offered by the bed nets.

Picaridin-based repellents can decrease 97% of mosquito bites within the first five hours of use and no observable change in efficacy over the time is seen.

Picardin is a commonly-used name for the compound ‘hydroxyethyl isobutyl piperidine carboxylate’. The official World Health Organization (WHO) approved name for the compound is icaridin.

Picaridin, used on human clothing and skin, repels ticks, insects, and chiggers. It is also recommended by the Centers for Disease Control and Prevention (CDC), to be used when travelling to areas with vector-based transmission diseases like Zika, dengue, and Lyme disease.

According to 2016 consumer reports, the picaridin-based insect repellents like Sawyer Picaridin and Natrapel 8 Hour with 20% Picaridin, are the best insect repellents available in the market today since they provided protection from mosquito bites for at least eight hours.

Picaridin and DEET are the two main chemicals currently used as insect repellents. WHO recommends use of both Picaridin along with DEET for protection against mosquitoes.

Picaridin however does not carry neurotoxicity concerns similar to that of DEET which is known to cause severe irritation and can potentially induce neurological damage with symptoms like tremors, slurred speech, and seizures.