Mosquito-Borne Brain Infection More Severe Than Thought

Mosquito-Borne Brain Infection More Severe Than Thought

Mar. 14, 2001 — You may never have heard of La Crosse encephalitis, even though it’s the most common mosquito-spread brain infection in the U.S. Now it looks like the disease — and its long-term effects on children — are more serious than once believed.

Connie Johnson of Charleston, W.Va., had never heard of it when her son Ronnie Mitchell, then 7 years old, came down with what her pediatrician said was a bad case of the flu. That was on a Thursday.

«Sunday morning, we were getting ready to go to church and I put him in the tub and he didn’t seem to know what to do with the washcloth or anything,» Johnson tells WebMD. «I called his name, and it was like he was trying to tell me something but his speech was garbled. We took him straight to the hospital and he had a seizure just as we went in. That Monday, he still was still not responding, and by that Wednesday it became so serious they called in a neurologist. They told me that it was a matter of life or death. One day he was OK, and two days later they are telling me he might die. Finally they realized it was La Crosse encephalitis. When you grow up you hear of snake bites, but never that a mosquito could bite you and you could die.»

La Crosse encephalitis now is firmly established in 28 U.S. states, mainly those in the Midwest and central Atlantic. Spread by a type of mosquito called the treehole mosquito, it nearly always affects children — and some of these children have long-lasting thinking and behavioral deficits.

James E. McJunkin, MD, and co-workers at the Health Sciences Center of West Virginia University in Charleston have treated 127 children hospitalized with La Crosse encephalitis from 1987 through 1996. Their report on these children appears in the current issue of TheNew England Journal of Medicine.

«Some children deteriorate after hospital admission,» McJunkin tells WebMD. «Fifty percent [show up] with seizure and 10-15% deteriorate with recurrent seizure or [brain swelling], usually within the first 72 hours of admission.»


The children ranged in age from 6 months to 15 years. None died, although several survived only because of aggressive intensive care.

Nearly as frightening is the finding from follow-up studies of 28 children who had the most severe symptoms. Many of these children had long-lasting changes in their behavior and ability to do their schoolwork. A normal IQ score is 100, but more than a third of these children had a full-scale IQ score of 79 or less.

«We found in following children over the long term that in about a third of children old enough to be tested, those children did seem to have suggestion of developmental problems, such as increase in hyperactivity measures in more than half of the kids,» McJunkin says. «There was also a suggestion of a decrease in average IQ compared to the norm.»

These changes aren’t always obvious at first.

«The problems were not there immediately,» Johnson says. «One year went by and then one day Ronnie was playing in the living room with his brother and fell on the couch. I thought he was joking, but then I saw he was out of it. The doctors realized he would start having more seizures at that point.

«I’ve cried about it — Ronnie seemed totally different from the son I had before,» she continues. «His whole attitude had changed. He seemed more defiant; he had learning impairments that we are still working on. He always had done really well in school, and it seemed after the encephalitis, he had no drive. It seemed he was always tired and always moody, not wanting to cooperate. But he’s starting to improve now.»

John R. Schreiber, MD, MPH, is chief of pediatric infectious diseases at Case Western Reserve University’s children’s hospital in Cleveland. He praises the McJunkin team for providing sorely needed information. He notes that while La Crosse encephalitis is a serious disease, other mosquito-borne encephalitic diseases firmly established in the U.S. can be far worse.

«The [aftereffects] of La Crosse encephalitis are worse than we thought but not devastating,» Schreiber tells WebMD. «In the scheme of things, these are mild deficits. For example, eastern equine encephalitis virus can destroy your brain — now that is very disturbing. In the fear ratio, La Crosse is considered relatively mild.


«I don’t keep my kids indoors when there is a report of La Crosse in the community,» he says. «But when it’s in the neighborhood, I make sure the kids are covered and wear insect repellant.»

For those most severely affected, however, the relative mildness of La Crosse encephalitis is small consolation.

Debbie Arrington’s son Josh, now 13, also came down with the disease when he was 7, just like Ronnie. The similarities didn’t stop there. «It was very, very scary,» Arrington tells WebMD. «The day [Josh] went into a seizure he was crying, ‘My head hurts so bad, please make it go away.’ I was rubbing his head and then he started just staring at the wall — it was a seizure, so we rushed him to the hospital. But when we got him home, that is when the struggle began. We did not get the same child back. He always forgot things, his schoolwork was very poor. A few months later he started having seizures again, and this continued every three months until last year.

«Now we know that God has blessed us,» she says, «and we have never had any more trouble. Now his memory is great, and he is 100% there. But it took us four years of hard work and positive reinforcement. It was a struggle to keep him going.»

Both McJunkin and Schreiber say it’s very important to keep mosquitoes from breeding around one’s home. The treehole mosquito loves to lay its eggs in old tires, but also likes small cups and flower pots. These should be removed. During mosquito season, insect repellent should be used — but make sure that the type and amount of repellent is appropriate for children.

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These Mosquito Bite Pictures Can Help You Identify Your Bug Bite

Plus, how to treat and prevent those annoying suckers.

There are endless reasons to love the outdoors—running in the fresh air, campfires, star gazing, hiking, chasing your pup, the list goes on. Sadly, enjoying the wilderness also means you turn yourself into an all-you-can-eat buffet for biting mosquitoes.

You know how it is: one minute you’re picnicking in the grass, and the next you’re scratching an itchy, red, swollen bump on your leg. Thankfully, mosquito bites are generally harmless—but there are instances where you might need to go to the doctor for that bump, versus just treating it as an over-the-counter cream situation.

Mosquito bites are kinda just part of life if you plan on stepping outside at any point—and the more you know about how to identify them, treat them, and prevent them, the less of a pain they’ll be. Your mosquito-bite guide, ahead.

What does a mosquito bite look like?

Most mosquito bites appear as firm, red, itchy bumps, according to Hari Nadiminti, MD, chair of dermatology at Summit Medical Group in New Jersey. Here’s the bad news: This means mosquito bites look a lot like the bites from gnats, fleas, and even spiders.

“It can sometimes be difficult to distinguish [them from] other insect bites,” says Dr. Nadiminti, “but the context can be an important clue to diagnosis.”

In other words, if you didn’t have a bite before you went to that late-night bonfire on the beach and now you do, a mosquito is the most likely culprit. Mosquito bites are also common when you end up in one of their habitats, like when you:

  • Spend time outdoors, especially at dawn and dusk when mosquitoes are active
  • Hang around standing or stagnant bodies of water (everything from backyard pools and birdbaths to marsh lands) where they breed
  • Walk or hike through tall grass and underbrush

In addition to the telltale itchy bump (which may be white and puffy or hard and red, depending on how long it’s been since the bite), other signs you’ve got a mosquito bite include blisters, dark spots, swelling, and hives, per the Mayo Clinic.

The Mosquito Bite Survival Guide

When A Mosquito Bites

Females are typically the only mosquitoes that feed on blood, and they do it because they need the protein to help develop their eggs. Without it, the eggs don’t mature to the point that the female mosquito can lay them for hatching.

The Female Tracks You Down By Sight, Smell And Feel.

Her head consists mainly of two giant compound eyes able to pick up movement and bright colors from long distances. From as far away as 120 feet, she can smell the carbon dioxide you exhale and the lactic acid that gathers on your skin from sweat. A little nearer, and your body heat begins to draw her like the “Hot Doughnuts Now” sign at Krispy Kreme.

The mosquito lights on your exposed skin and slides a serrated proboscis into you, searching for a capillary. At the same time, she injects saliva that contains enzymes to dull the pain and keep your blooding from clotting. Left uninterrupted, she will draw blood until her abdomen is full.

What Do Mosquito Bites Look Like?

Those enzymes are the problem.

Your body doesn’t like them because they are foreign invaders, so your mast cells release histamine, a naturally occurring substance which rushes to the site and causes blood vessel to enlarge. Sometimes the body releases too much histamine. The result is mosquito bite swelling, or what’s called a “wheal.” The area around the bite rises, turns red and begins to itch.

How much and for how long varies from person to person, but swollen mosquito bites generally are about the size of a dime and last about a day. Doctors at the Mayo Clinic report that, in some people with extreme sensitivities, mosquito bites can swell to the size of grapefruits and linger for days.

And occasionally, there are people who experience anaphylaxis, a severe reaction to mosquito bites. When that happens, the person’s throat can swell shut, restricting breathing, the person’s skin may break out into hives – itchy red bumps – anywhere on the body, not just at the bite. While rare, the reaction can be life-threatening, according to the Mayo.

WebMD reports that repeated mosquito bites over a lifetime may help people become immune to the saliva, or can have the opposite effect, making a person even more sensitive.

Sweet Relief: How To Stop Mosquito Bites From Itching

There are a lot suggestions for soothing the discomfort of an allergic reaction to a mosquito bite. Some are common-sense, some medical and some just a little odd. But they all have advocates who swear they work. Among The Suggestions:

  • Don’t scratch the bite. That only irritates your skin further and could lead to infection. Give it a light washing with soap and cool water.
  • Try calamine lotion. The pink goo, a favorite of moms everywhere, is a mixture of zinc oxide and iron oxide and works as a cooling, all-purpose soother. The Food and Drug Administration declared in the early ’90s that it’s ineffective in treating itches, but doctors still recommend it. You might also try Caladryl, which contains both calamine and an analgesic to help relieve the sting.
  • Apply an OTC hydro-cortisone cream. The cream contains corticosteroids which will counteract the effect of the histamines and help reduce the swelling, which should give you some relief from the mosquito bite itch. An anti-inflammatory such as ibuprofen will also help.
  • Use a cold compress or ice pack. Histamines dilate the blood vessels, filling the affected area with excess blood. Cold causes the vessels to constrict, so that the amount of blood is reduced around the bite.
  • Take an antihistamine. This won’t work immediately, but an OTC medication like Benadryl will prevent histamines from binding with receptors at the blood vessels. The vessels in the bite area return to normal, and the swelling and itching dissipates. Remember, you can take an antihistamine before going outside to minimize your allergic reaction to a mosquito bite.
  • Dab on some baking soda paste. For some reason, the Mayo Clinic doctors – and dozens of home-remedy advocates – suggest adding a bit of water to regular baking soda, then applying the paste to the mosquito bite. The reason isn’t clear, but it apparently helps relieve the itch.
  • Heat up a spoon and apply to the bite. The heat will destroy the protein that caused the reaction and the itching will stop.
  • Go homeopathic. Suggestions range from rubbing the bite with the inside of a banana peel to dabbing on toothpaste to covering the bite with mud. Dr. Alan Greene, pediatrician and prolific health writer, suggests that some natural anti-inflammatory remedies such evening primrose oil may also help reduce the swelling and itching associated with mosquito bites.
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These are some of the steps you can take in the hours immediately after a bite. But remember, if you start feeling sick in the days ahead, particularly if you feel flu-like symptoms that include neck stiffness, headache, nausea and fever, then it’s possible that mosquito bite left you with something worse than just an itch. Go to the doctor. Period!

But Wait. Why Not Just Prevent Mosquito Bites?

The best way to treat a mosquito bite really is to avoid getting bitten in the first place. Simple as it sounds, this can be a real challenge, especially during the summer or in warm climates.

Obviously, you’ll want to avoid the places where mosquitoes tend to congregate – which is anywhere near water.

If you don’t have to be around swamps, marshes, rivers, canals, lakes and ponds, then don’t. Otherwise, at least get clear of the water from dusk until a few hours after dark, when the bugs are out hunting for blood meals.

Unless you take certain precautions, you may also have to abandon your own backyard during the evening hours, so you’ll need to do some work on your environment:

  • Get rid of any standing water around the yard because it will become a breeding ground for mosquitoes. Keep the grass and bushes trimmed so they don’t have resting places. Make sure all your windows have screens, and that they are in good shape, and consider screening in the back porch or deck.
  • Install a mosquito control device, such as a mosquito trap that uses light, gas emissions and heat to emulate a mosquito’s human targets. The traps attract the mosquitoes, then kill them before they get to you. You can use these devices in conjunction with citronella candles that are reported to repel mosquitoes and subdued lighting or yellow outdoor bulbs that aren’t as likely to draw hungry insects.
  • When you do go outside, try to keep as much of your skin covered as possible, and avoid bright colors that will attract the attention of mosquitoes. Use an insect repellent containing DEET on the bare areas.
  • Dr. Greene also recommends vitamin B1 (25 to 50 milligrams three times a day) or garlic to produce a skin odor that is supposed to naturally repel mosquitoes. It takes about two weeks of regular doses for the B1 to become effective, he says.

The bottom line is, there’s just no way to guarantee that you’ll never feel the sting of a mosquito feeding on your blood. The occasional mosquito bite is inevitable, and that’s how it is. But there’s no reason you have to suffer.

Hopefully, you can use some of these tips to get a little relief when it happens.

11 Ways to Prevent Mosquito Bites That Actually Work, According to Entomologists

Stocking up on the right repellent is only the first step in preventing a painfully itchy bite.

This article was medically reviewed by Shonda Hawkins, MSN, a nurse practitioner and member of the Prevention Medical Review Board, on June 11, 2019.

It’s backyard barbecue season—but you’re not the only one planning a feast. The mosquitos are out and ready to chow down. But before you fill another shopping bag with citronella candles, it’s important to understand your adversary.

When a mosquito lands on your skin, it will feed on your blood—but once it leaves, the proteins in its saliva stay behind. Your immune system sees this is a threat and pumps out histamine (the same response it has to allergens) to attack these proteins. The result? Those unbearably itchy, red welts you remember scratching at as a kid. Luckily, there are ways to get rid of a mosquito bite quickly, and the itching should go away within two to three days.

But it’s not just bites you need to worry about—the aftermath can be unpleasant, too. Mosquitos can carry all sorts of intense diseases, like the West Nile or Zika viruses, or even chikungunya and malaria (which are risks if you travel to certain countries). That’s why preventing mosquito bites in the first place should be a priority during the warmer months.

Entomologists know how these insects operate, which is why we consulted several for the dos and don’ts of repelling these pesky pests.

Almost any breeze—anything above 1 MPH—makes it very difficult for mosquitoes to fly, says Jonathan Day, PhD, a mosquito expert and professor of medical entomology at the University of Florida. If you can pick a breezy spot for your summer outing, that can help prevent mosquito bites.

Plug-in fans are also a great deterrent, he adds. Just keep the flow of air directed at the lower half of your body; mosquitoes tend to fly very close to the ground to avoid wind, so directing the fan’s force downward will block their approach.

Natural wind or a fan will work much more in your favor than those fancy, ultrasonic devices and apps marketed as mosquito repellants—some of which claim to mimic the sound of dragonflies. “They don’t work at all,” Day says.

Just like you, mosquitos crave a meal during certain times of day, says Howard Russell, an entomologist at Michigan State University. And for these critters, it’s often around dusk and dawn.

That’s because the wind typically dissipates as the sun rises and sets, which brings mosquitoes out to feed, Day explains. If you can try to stay inside during these times when the weather is warm, you’ll be able to prevent more than a few mosquito bites.

DEET has a bad reputation, but adverse reactions to it are rare—and tend to occur only when people swallow or snort the stuff. When used as directed, it’s extremely effective, since it blocks a mosquito’s CO2 receoptors, Day says. Still, he’s quick to add: “Most people don’t understand how to apply it properly.” (Fun fact: DEET makes a great tick repellent, too.)

First, you should not spray DEET on your body and clothes like it’s perfume, he stresses. Instead, squirt a little onto your hands and rub it onto your ankles, elbows, wrists, forehead, and all the other places where your skin is thin—and where mosquitoes love to feed.

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Also important: Day says a product’s DEET concentration determines how long it will last—not how well it will work. If you’ll be outside for 90 minutes or less, he says a product with 7 to 10 percent DEET will do the job, and you can always reapply to extend its efficacy (do not go higher than 30 percent). DEET in lotion or wipe form is also just as effective as a spray and removes the risk of inhaling it.

Finally, don’t waste your money on wearable DEET items, like wristbands or anklets—they don’t actually prevent mosquito bites, says Day.

If you just can’t with DEET, there are other options that are recommended by the Centers for Disease Control and Prevention (CDC) for use in repelling mosquitos, including:

While all of the above have been found to be effective like DEET, Pereira recommends using picaridin. “This is something that was developed for the military just like DEET was,” he says. “It works really well.”

If you’re at the store and you’re not sure if a repellent has these ingredients, “your safest bet is to look for Environmental Protection Agency approval on the product’s label,” says Nancy Troyano, PhD, a board-certified entomologist with Ehrlich Pest Control. If it does, it should be effective and safe. (You can also search products registered with the EPA here.)

This can be easier said than done in the summer, but mosquitos are drawn in by pheromones released in your sweat, says Roberto M. Pereira, PhD, an entomologist and research scientist at the University of Florida.

This can vary from person to person. “Some people, like me, attract mosquitoes regardless of what they drink, eat, or wear,” says Russell. Still, the more you can do to take it easy on the sweating—especially during peak mosquito hours—the better.

Mosquitoes can’t penetrate clothing that has a very tight weave, Day says. While cotton and linen typically aren’t great armor against mosquito bites, Day says many synthetic fibers—particularly high-tech athletic apparel—tend to be woven tightly enough to keep bugs out. Any garment that offers sun protection will also have a tight enough weave to prevent mosquito bites, especially when you opt for long sleeves and pants.

Mosquitoes also use their vision to search for food sources during the daylight hours. Since they fly very close to the ground, they tend to find targets by looking for things that contrast with the horizon, Day says. “Dark colors stand out, but light colors are less attractive to them,” he adds. Of course, make sure you protect any exposed areas with a repellent if you’re going to be spending time outdoors for a long period of time.

Day says carbon dioxide (CO2) is the primary thing mosquitoes search for to identify food sources. And when your heart rate is elevated, your body produces more CO2. From exercise to drinking alcohol to eating spicy foods, anything that cranks up your metabolic rate will increase your CO2 production—and make you irresistible to mosquitoes, Day says. Unfortunately, being overweight or pregnant can also up your CO2 output, he adds.

If you’re outdoors and you know your heart rate will be spiking, make sure you wear protective clothing or apply a repellent to keep bug bites at bay.

There are different types of mosquitos, and the “mosquitos that we worry about in urban areas are usually ones that are being produced in your own backyard,” Pereira says. Aedes mosquitos, which transmit Zika virus and chikungunya, can easily breed in small containers of water like a birdbath or even water sitting around your plants. “They can breed in your own yard, and you wouldn’t necessarily know it,” Pereira says.

Do your best to clear out any standing water to lower the odds that you’ll have lots of mosquitos hanging around your place ready to bite.

This shouldn’t be your only mosquito-combating strategy, but Pereira says that certain plants may help discourage mosquitos from hovering near your house. Those include things like citronella, lavender, lemongrass, marigolds, and basil. “If you had enough, it could make a difference in terms of mosquitos inside your property,” he says.

Just keep realistic expectations about what these can and can’t do, Troyano says. While they may help tamp down on the number of mosquitos around your place, “even planted in large quantities, the potency of these plants would not be enough to keep mosquitoes out of your yard entirely,” she says.

The same goes for citronella candles and oils. While they’re natural insect repellents, Day says they only work if their scent or smoke gets between you and the mosquito. So if you’re lighting tiki torches that sit a few feet off the ground, they won’t do much to prevent mosquito bites, he says.

If you live in an area where the mosquitos are unbearable, it might be worth hiring a professional to come and treat your yard with insecticide, Russell says. This can do a pretty good job of ensuring they won’t come anywhere near your place.

As for mosquito traps? They’ve been souped up with fancy features to attract mosquitoes with special lights, heats, or scents. “There’s no doubt that traps can—under the right environmental conditions—capture of a lot of mosquitoes,” Day says. Realistically, though, you can’t catch ‘em all. “Over the last 30 years, there have been many traps marketed as being able to clear a one-acre or five-acre lot,” Day says, “and it has never been my experience, even with very efficient traps, that they can rid a whole area of mosquitoes.”

A trap in the middle of your backyard will kill mosquitoes that fly close enough to sense its lures, sure, he says, but countless more will come flying into your yard to fill the space they leave behind. Mosquitoes are also adept at telling the difference between a trap and a living, breathing host—aka you.

This can be tough, but it’s definitely worth a try if mosquitos are terrible in your area. “Any scented perfume, lotion, or soap could potentially attract mosquitoes,” Troyano says. “If you want to reduce your attractiveness to mosquitoes, avoid scented products in general.”

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