DEET

Worm Study Raises Concern About DEET’s Effect on Reproduction

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Findings suggest need to consider reproductive health alongside prevention of insect-borne diseases

white woman wearing a backpack, viewed from behind, spraying insect repellant onto her bare forearm in a field next to some woods


Researchers have uncovered evidence hinting that the most common bug spray ingredient, DEET, might cause reproductive problems by affecting the formation of egg cells during pregnancy.

The findings come from a study in C. elegans — worms that don’t look like they have much in common with humans yet serve as surprisingly usefulbellwethers of how toxins in the environment affect human reproduction.

The research, published Jan. 4 in iScience, raises difficult questions. Chief among them is how to balance the possible reproductive harms of DEET-containing products in people — including infertility, miscarriage, or birth defects — with the need to ensure that people remain protected from diseases transmitted through insect bites, such as malaria, Lyme disease, West Nile virus, and Zika virus disease.

Whether and how much DEET use causes reproductive problems in humans will need to be confirmed in future studies. Such studies have been scarce to date in humans because of the ethical concerns involved.

Harvard Medicine News spoke with study senior author Monica Colaiácovo, professor of genetics in the Blavatnik Institute at Harvard Medical School, about what her team found and what it means.

Harvard Medicine News: Why did you conduct this study?

Monica Colaiácovo: The biggest motivator was how high DEET scored in our initial screens of how various chemicals in our environment affect meiosis, using the model organism C. elegans. Meiosis is the type of cell division that creates eggs and sperm. DEET was one of our top hits in terms of chromosomes not separating properly, so eggs end up with abnormal numbers of chromosomes. In humans, this can cause miscarriage, stillbirth, infertility, and genetic conditions such as Down syndrome. We knew we had to look at this carefully.

Screen shot of a woman in an office (Monica Colaiácovo) mid-explanation. She has shoulder-length brown hair and is wearing a blazer

Learn about the worm-screening method the Colaiácovo lab developed to quickly identify chemicals that affect meiosis.

Research has shown that DEET products can have neurologic effects on people who use them, but no one had really looked at what DEET is doing in meiosis. We wanted to understand whether it would cause a problem. Only a few human studies have been done, and practically everyone uses DEET, so the possibility that it could affect reproduction felt palpable for people in our lab.

HMNews: What did you find?

Colaiácovo: Using our worm model, we showed for the first time that DEET can have effects on meiosis. Then we showed why.

We saw that DEET has a significant impact on gene expression — the pattern of genes that are active or inactive in a cell. We found that the change resulted in oxidative stress (an imbalance between free radicals and antioxidants) and abnormal structure of the materials that form chromosomes, which compromised the ability of chromosomes to separate properly as the cell divided. Egg cells and the worm embryos they gave rise to were less healthy.

Five side-by-side microscopy images with microtubules (stained green) pulling apart chromosomes (stained red) during egg cell division. The left two separate normally. The right three show disorganization
Left two images: Normal chromosome separation during meiosis in worms. Right three images: DEET exposure caused a variety of disruptions. Images: Nara Shin


HMNews: How applicable are the worm findings to humans?

Colaiácovo: That is always the big question. Many human genes have equivalents in C. elegans, and worms are a powerful model for looking at effects on reproduction. C. elegans have been instrumental in uncovering how environmental toxicants such as the plastics chemical BPA can harm reproductive health.

We observed the changes in meiosis when the levels of DEET inside the worms were the same as, and in some cases lower than, what you find in blood or urine samples from the regular human population. That said, the paradigm for exposure wasn’t the same as it is for most people. The worms were exposed to DEET for 24 hours at a time, which may not apply to anyone, or apply to only certain groups, such as agricultural workers. And there are some metabolic and physiological differences between worms and humans.

A very important thing from our studies is that we’re providing reproducible, well-controlled, substantial data. Other groups can take up this work in mice or other animal models and further advance our understanding of what DEET may be doing in human reproductive systems. We can also build on this evidence to flag chemicals of concern for policymakers.

Four side-by-side microscopy images show individual cell nuclei in C. elegans worms. The left one is normal. The right three show gaps, aggregates, and other abnormalities
DEET exposure led to missing, aggregated, and abnormal eggs in the worms. Images: Nara Shin


HMNews: At this stage, how would you frame recommendations for people? How do you balance reproductive health with prevention of diseases from mosquitoes and ticks?

Colaiácovo: My family is from South America, where Zika and dengue, for example, are common, and I want to make sure people are not scared away from being careful. So-called tropical diseases transmitted by insects are moving into new regions of the world as the climate changes, putting more and more people at risk. The consequences of stopping the use of insect repellents can be very serious

So, we want prevention. We want repellents. And DEET is a very effective option we have right now. At this moment, I would say we should be aware of the potential reproductive risks of DEET-containing products and be sure to follow the application instructions when using them. Our work suggests this is very important for pregnant women because female meiosis begins in the developing fetus in the womb.

I would love to see research give rise to best practices for applying DEET products during pregnancy, when there’s often so much confusion and anxiety about what to do or not do.

I also hope our work helps drive the development of DEET alternatives that are safe and effective. It would be great to have an effective insect repellent that doesn’t make us worry about our health or that of our children.

A New Study Shows Mosquitoes Can Be Trained Not to Bite Specific Humans

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IN BRIEF

Mosquitoes transmit dangerous diseases, killing more people than any other animal and prompting the recent War on Mosquitoes. A new study shows that a method for training mosquitoes not to bite specific humans could be as effective as using insect repellents like DEET.

WAR ON MOSQUITOES

A graphic from Bill Gates’ blog clearly illustrates that the mosquito causes more deaths per year than any other animal on the planet. This killer insect has a nasty reputation for spreading the disease around the globe, prompting what some have called The War on Mosquitoes. A recent experiment could be a turning point in this battle, as it equips us with a surprising and potentially revolutionary weapon — the ability to train mosquitoes.

According to a study published in Current Biology, when you slap at a mosquito that is about to bite you, it learns to associate your personal scent with that life-threatening experience and will avoid you in the future. This is the first demonstration showing that mosquitoes are able to both learn and remember.

It turns out that mosquitoes can learn and remember. Image Credit: WikiImages / Pixabay
It turns out that mosquitoes can learn and remember. 

As described by Jeff Riffell, the study’s lead researcher and University of Washington neuroecologist, in an interview with National Geographic, “They’re essentially Pavlov’s mosquitoes.” He is referring to the famous experiment in which dogs are trained to salivate on command, which is comparable to mosquitoes being trained to avoid certain humans.

TRAINING INSECTS

Mosquitoes don’t bite at random. They are drawn to specific scents which are more alluring than others. The human scent, generally speaking, is particularly attractive to mosquitoes. But, when a person slaps at a mosquito, they usually create small vibrations on the skin that interrupt the insect’s attempt to bite.

The Worst Bug Bites in the World [INFOGRAPHIC]

In this study, the researchers recreated these vibrations in 20-minute sessions and found that, when the mosquito bite was disturbed by these vibrations, the insect avoided that scent for up to 24 hours. This level of effectiveness was even likened to publicly-available insect repellent that contains DEET.

While there is still a great leap between this research and an improved method for combating mosquito-transmitted illnesses, Walter Leal, who studies human-mosquito interactions at the University of California, Davis, but is not an author of this study, is optimistic. He stated to National Geographic that “Now that we know that some compounds trigger this memory of avoidance, one could possibly use a formulation that not only includes an active repellent, like DEET but also includes some compound that would trigger the memory of avoidance.”

CDC confirms lemon eucalyptus oil as effective as toxic DEET for repelling bugs

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DEET, while amazingly effective at warding off mosquitoes, comes with its own dangers.

It’s a neurotoxin.  Found in most conventional, over-the-counter insect repellents, it can enter your bloodstream if it comes into contact with your skin.  Children with DEET toxicity have reported lethargy, headaches, tremors, involuntary movements, seizures, and convulsions.

It is, then, a refreshing admittance that lemon eucalyptus oil is as effective as this toxin in repelling mosquitoes.

“Oil of lemon eucalyptus [active ingredient: p-menthane 3,8-diol (PMD)], a plant- based repellent, is also registered with EPA. In two recent scientific publications, when oil of lemon eucalyptus was tested against mosquitoes found in the US it provided protection similar to repellents with low concentrations of DEET,” according to the article on Mattermore.

Finding natural solutions and substitutions for heavy chemicals and toxins is extremely important and being able to research them on the internet has allowed us to swiftly rectify any time this is the case.  Businesses and organizations have begun selling lemon eucalyptus oil repellents and the non-toxic movement has taken off.

How To Keep Mosquitoes Away: Consumer Reports Reviews Bug Sprays, Says DEET Is Not The Winner

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Spring sunshine will soon give way to summer, and for most people that means even more time spent in the great outdoors. Natch, your most pressing concern is bug spray. No one wants to be eaten alive by insects, so which repellent works best? Turn to Consumer Reports, venerable resource and reviewer of all products, for the answer.

With their usual thoroughness, CR tested bug repellents with great focus on all the nitty gritty details. They began with, in their own words, “an 8-cubic-foot cage containing 200 disease-free, female mosquitoes in need of a blood meal to lay their eggs.” (Yes, “blood meal.”) CR chose culex mosquitoes, which are known to transmit West Nile virus, and aedes, which carries chikungunya. The former bug is most active between dusk and dawn, the latter all day long. Both enjoy humans.

Next comes the squirm-inducing part. After applying a different repellent to each forearm, the testers waited 30 minutes and then plunged their arms into the cages filled with blood-lust mosquitoes. Meanwhile, CR experts, presumably wearing spectacles and sporting clipboards, watched and recorded bites.

Rules of the game: If a tester was bitten two or more times in one five-minute session, or once in two consecutive sessions, a repellent failed. To analyze how the repellents worked against ticks, the experts marked three lines on each tester’s bare arms and  then released, one at a time, five disease-free deer ticks to crawl on them. Here, a repellent failed if two ticks crossed into the treated area.

So, what did they discover? Failures included the many products listing plant oils, like citronella, lemongrass, and rosemary, as their main ingredient. None of these effectively guarded against mosquitoes and ticks — some failed to defend the testers against the aedes mosquitoes for even half an hour. Candles and wristbands also proved to be ineffective.

The top-performing product was Sawyer Fisherman’s Formula, which held mosquitoes and ticks at bay for eight hours.

Second runner-up was Repel Lemon Eucalyptus, which protected against ticks for eight hours and mosquitoes for seven hours.

So, what made the winners winning? Quite simply, they contain 20 percent picaridin and 30 percent oil of lemon eucalyptus.

While two DEET products — the most common mosquito and tick repellent on the market — also earned good scores, they were not as effective as the picaridin and oil of lemon eucalyptus. Possibly because of its inactive ingredients, the 25 percent DEET product performed less effectively than the 15 percent DEET product. None of the products containingIR3535, which is often included in sunscreens even if many claim this chemical to be an eye irritant, made the list.

New mosquito repellent is ultra-effective – Australian Geographic

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A new vapour developed in the USA renders humans virtually undetectable to mozzies.

SCIENTISTS HAVE CREATED WHAT might be the most effective insect repellent ever.

While the majority of existing repellents create an odour that is unpleasant for mosquitos, using a yellow oil known as DEET, this new blend of chemicals renders the insect senseless.

“These chemicals make you invisible,” says Dr Ulrich Bernier, a research chemist at the United States Department of Agriculture research service, and creator of the new formula.

Most effective mosquito repellent?

With over 5000 reported cases of mosquito-borne Ross River and Barmah Forest viruses in Australia every year, this new formula could prove to be invaluable for Australians in rural and urban areas.

Mosquitoes find humans by honing in on various chemicals and bacteria on the skin. In 2000, while studying this process, Ulrich created a repellent consisting of several chemicals, all of which are found in low doses in the human body. The resulting repellent was somewhat effective.

Years later, Ulrich added additional chemicals to the formula, including homopiperazine and 1-methylhomopiperazine, similar to those found in the human body, which acted to mask the scent of humans. He was amazed by the results.

“We took a cage of mosquitoes and gave them two ports to fly into: one with human hands inserted into them, and the other one with nothing.” At first, Ulrich explains, the mosquitoes were attracted to the container with the human hands. After the repellent was sprayed, however, they approached the containers with equal interest.

Researchers are keeping close guard over the ingredients of the formula, which was patented last year.

Repellent in vapour form

Significantly, this new repellent will be sprayed into the air, as opposed to directly on the skin.

Dr Cameron Webb, a medical entomologist at Sydney University, says that while DEET-based sprays have proven to be adequate in preventing mosquito bites, this new development represents an important next-step in insect-borne disease control.

“When applying lotions or sprays onto the skin, one can easily miss a spot,” says Cameron. “Air-based repellents solve that issue.”

The new repellent will take the form of a vapour which will work to create a protective bubble. While DEET has been accepted as a safe means of repellent, Ulrich says it’s always safer to have chemicals further away from humans.

Commercial availability is still a ways off, however: Ulrich says more field tests and toxicology tests are necessary to ensure the product is completely safe before it can hit the market.

The Rising Threat of West Nile Virus.

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Mosquito bites are the scourge of everyone’s summer. The rising risk of West Nile virus that comes with the bites just makes them that much worse.

The last few years have seen outbreaks of West Nile in different locations around the country, so researchers at the Centers for Disease Control and Prevention and the U.S. Public Health Service recently did a review of the scientific literature on the mosquito-borne virus.

“I did a similar literature review ten years ago in JAMA,” Lyle Petersen, corresponding author on the study, told TheDoctor. Since that time, he went on to say, researchers have learned a lot more about the virus and how it behaves in the U.S..

The virus is able to establish itself in a wide variety of ecosystems, leaving the whole continental U.S. basically at risk.

A lot of people have been infected, and most likely, more than 1 million people have been made ill from West Nile virus, the scientists found. This is quite a high rate of transmission for an imported mosquito-borne virus coming into the country for the first time, Petersen, who is the director of the Division of Vector-Borne Diseases at the CDC, said. Mosquitoes are the most common, but not only, way the virus is transmitted.

Symptoms

According to Petersen, even though about 3 million people have been infected, 98 percent or 99 percent of the population is still susceptible to infection with the virus, so prevention methods are just as important as ever.

About 1 in 5 people who are infected will develop a fever with other symptoms such as headache, body aches, joint pains, vomiting, diarrhea, or rash.

The CDC estimates that most people (70-80%) who become infected with West Nile virus do not develop any symptoms. About 1 in 5 people who are infected will develop a fever with other symptoms such as headache, body aches, joint pains, vomiting, diarrhea, or rash. Most people with this type of West Nile virus disease recover completely, but fatigue and weakness can last for weeks or months.

Less than 1% of people who are infected will develop a serious neurologic illness such as encephalitis or meningitis (inflammation of the brain or surrounding tissues). Severe neurological symptoms can include headache, high fever, neck stiffness, disorientation, coma, tremors, seizures, or paralysis.

People with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants, are also at greater risk for serious illness. Recovery from severe forms of the disease may take several weeks or months. Some of the neurologic effects may be permanent. About 10 percent of people who develop neurologic infection due to West Nile virus die.

Location, Location

The researchers found that the virus has become widespread, and is now circulating every year across almost the entire continental U.S.. That West Nile has managed to cause outbreaks in places like Phoenix, a city in the middle of the desert and also in cities with completely different climates, like Chicago or New Orleans, is “pretty remarkable,” Petersen said. The virus is able to establish itself in a wide variety of ecosystems, leaving the whole continental U.S. basically at risk.

We expect that the number of cases, based on historical precedence, will begin to increase over the next several weeks.

Certain areas of the U.S., such as California and the Midwest, seem to be at higher risk for having sporadic outbreaks; however, outbreaks have occurred in many different places across the country, and some of them, such as Phoenix, are quite surprising. It is still very difficult to predict where outbreaks will occur, and they can happen anywhere.

The timing of outbreaks is amazingly consistent from year to year. They begin to increase at the end of July, peak somewhere around the beginning to middle of August, and then taper off into September. And they occur a little earlier in the southern U.S. than the northern region of the country. “This means that we expect that the number of cases, based on historical precedence, will begin to increase over the next several weeks, which means that people need to take precautions right now.” according to Petersen .

Some of the emergency control efforts that cities have taken, such as widespread pesticide spraying, are effective in stopping outbreaks when they do occur, says Petersen. Several studies have looked at the health effects of pesticide spraying, and found that there have been no short-term health effects from spraying to control West Nile outbreaks.

Don’t Be Bug Bait

Mosquitoes that spread West Nile virus are most active around dawn and dusk, although they can be out all night. If you go outside where mosquitoes are present, wear insect repellent. That is the single most important thing someone can do.

“We recommend products that contain N,N-diethyl-meta-toluamide, commonly called DEET,” says Petersen. “A lot of misinformation exists about DEET. People think it is dangerous. The reality of DEET, though, is that is actually one of the safest chemicals that people apply to themselves.”

If you go outside where mosquitoes are present, wear insect repellent. That is the single most important thing someone can do.

DEET-containing products are also much more user-friendly than they used to be, says Petersen. People think of them as oily and bad-smelling. But newer products are much more pleasant to use.

Petersen says that the higher the concentration of DEET, the longer it lasts, until the concentration gets up to about 40 percent. “I wouldn’t advise products that are 100 percent DEET, because they really do not work any better. You should look for products that contain 10 percent DEET if you are only going to be out for a short time, and 30 to 40 percent DEET if you will be out for longer periods.”

“We also recommend products that contain picaridin, oil of lemon eucalyptus, orIR3535,” says Petersen. These products are registered with the EPA and are known to be effective. It is easiest to remember DEET, though, and physicians and public health officials have the most experience with DEET.

Source: JAMA