Tue | Aug 14, 2018

What the mosquito killers aren't telling you

Published:Sunday | September 28, 2014 | 12:00 AM


I think Dr Fenton Ferguson, the minister of health, will agree with the rest of us that the number of chik-V sufferers in the country now exceeds 35. Everyone is now living in fear of mosquitoes.

An obese adult mosquito weighs 2.5 milligrams. The annoying buzzing we hear is from its wings, which beat at up to 600 times per second. As you may guess, it is the females that are attacking us. The males are quite satisfied with the nectar from flowers. And they are romantic, too. When they find a mate, their buzzing synchronises to the same speed. But before you fall in love with them, there is something else you need to know. Carrying any number of deadly diseases, including malaria, dengue fever, yellow fever, and encephalitis, more deaths are associated with mosquitoes than any other animal on the planet.

The number of persons who now claim to be suffering from this virus is reaching alarming proportions. I frequently hear exhortations in media presentations to purchase repellents containing DEET. The most effective repellents are usually those that contain high levels of DEET, an organic compound. The chemical name for DEET is N,N-diethl-meta-toluamide, and it is a derivative of toluene.

Last year, however, a Duke University Medical Center pharmacologist, Mohamed Abou-Donia, recommended caution when using the insecticide DEET, after his animal studies found the chemical causes diffuse brain cell death and behavioural changes in rats after frequent and prolonged use. He also called for further testing of the chemical's safety after short-term and occasional use. It is worthy of note that Health Canada has banned products with more than 30 per cent of the chemical.

Abou-Donia's numerous studies in rats (he has been doing this for 30 years) clearly demonstrate that frequent applications of DEET cause neurons to die in regions of the brain that control muscle movement, learning, memory and concentration. Rats treated with an average human dose performed far worse than controlled rats when challenged with physical tasks that require muscle control, strength and coordination. Those persons who wish to read further on the subject will find that these effects are consistent with physical symptoms in humans reported in the medical literature

Concerns about the dangerous effects of DEET did not just start with the Duke study, however. About 15 years ago, a 27-year-old man applied Deep Woods Off (20% Deep) and went fishing. He soon developed an altered mental state and paresthesias (tingling, pricking and burning sensation). This progressed to auditory hallucinations and severe agitation. He was heavily sedated when he reached hospital and required mechanical ventilation. He was released three days later with no recurring symptoms. This is just one of several recorded cases.

In 1992, a 34-year-old expectant mother, while working in Africa, applied lotion containing 25 per cent DEET daily to her arms and legs in addition to taking chloroquine. There were no complications during pregnancy. When the child was born, however, an antimongoloid slant of the palpebral fissures (opening between the eyes), hypertelorism, (abnormal distance between two organs, e.g., eyes), thin lips, poorly developed philtrum (vertical groove in the upper lip), and a broad nasal bridge were observed. The child developed muscular hypotomia (reduced muscle strength), central hearing loss and strabismus ('cyaas eye'). Results of extensive examination (Schaefer and Peters, 1992) concluded that the use of DEET might have played a role in the occurrence of the reproductive effects.

Most of the cases of significant toxicity from DEET exposure are in children under the age of eight. The most frequently reported symptoms of DEET toxicity in children are lethargy, headaches, tremors, involuntary movements, seizures and convulsions. These are some of the complaints I hear daily that are attributable to the virus and not to DEET - the possible culprit.

How it work?

On Wednesday, a worried mother held up a repellent and asked a perplexed clerk in a pharmacy, "How it work"? Maybe I can help them both.

Mosquitoes and other insects like ticks and flies detect you by the smell of carbon dioxide emitted from your body. They can pick up the scent 75 feet away. Since DEET is an aromatic compound with a strong odour, it helps mask the odour of carbon dioxide, and in the process makes it impossible for insects to detect your presence.

Mosquitoes are particularly attracted to hot, active, sweaty people, especially those who can't or don't like to bathe. They find 'cheesy' feet and dirty socks irresistible. Oh! And they just love dark clothing.

Most of the studies I have read on the subject contain long, boring words. What they are saying in English is that the topical repellents containing DEET can cause long-term side effects, sometimes years later. This is because of the fact that nearly 50% of the chemical penetrates the deeper layers of the skin, and around 15 per cent of it into the bloodstream. This can adversely affect the skin and prove toxic to the body.

Our children are the most vulnerable, as their tender skin absorbs substances more readily. Toxic substances have been known to affect the nervous system and even growth rate.

The question that now comes to mind is, 'Do we need DEET to avoid insects?' The answer is no. There are plants natural products with absolutely no side effects that can do the work. Plants like tansy, marigold (African preferably), cedars, lemon grass, sage, garlic, geranium, basil and mint can be planted around the house. A study done at the University of Guelph found that lemon thyme had 62 per cent of the repellency of DEET. Nepetalactone, the essential oil that makes catnip smell the way it does, was found by Iowa State University researchers to have about 10 times the repellency of DEET. Plant them!

There are mixtures of essential oils that can do the job just as well. The only setback is that they have to be applied more regularly - say, every two hours. Use 10 to 25 drops of essential oil to two tablespoons of carrier oil. The best essential oils against mosquitoes are cinnamon, citronella, lemon and pyrethron from the flowers of the daisy. Some carrier oils are olive, sunflower, witch hazel and, if any is left, good old vodka.

Perhaps those in the relevant places can check to verify my claims. Commonly used preparations like insecticide-based lice-killing shampoos and insect repellents are assumed to be safe because severe consequences are rare in the medical literature. Yet subtle symptoms like muscle weakness, fatigue or memory lapses might be attributed erroneously to other causes. Several overt symptoms are not seen immediately after use but may manifest themselves months or years later, making a cause-and-effect relationship difficult to establish.

As the number of chik-V cases grow, I suspect that parents and sufferers are going to self-medicate and go overboard with dosages and other experiments. They must be warned. Alternatives must be provided, or at least suggested. Pregnant and nursing women and children under eight years old are particularly vulnerable.

Glenn Tucker is an educator and sociologist. Email feedback to columns@gleanerjm.com and glenntucker2011@gmail.com.