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Rx for health: Bug spray

Kemperman specializes in diseases carried by ticks and mosquitoes. Kemperman holds a master's degree in epidemiology from the University of Minnesota and a bachelor's degree in biology from Macalester College in St. Paul. She has monitored tick a...

Kemperman specializes in diseases carried by ticks and mosquitoes.

Kemperman holds a master's degree in epidemiology from the University of Minnesota and a bachelor's degree in biology from Macalester College in St. Paul. She has monitored tick and mosquito-borne diseases in Minnesota for the last three years.

There is a peak in the number of mosquitoes that carry the West Nile virus this year, Kemperman warns. While West Nile seriously affects only about 1 percent of those who are infected, a somewhat higher percentage develop unpleasant symptoms.

Kemperman spoke with Herald Staff Writer Dorreen Yellow Bird.

What is West Nile?


West Nile is a virus transmitted to people through the bite of an infected mosquito. When someone is bitten, do they always get West Nile?No. Most people bitten by a West Nile mosquito won't have any symptoms at all. For those who do have symptoms, the majority will have a milder form of West Nile called West Nile fever, which still isn't fun to have. You still feel sick.

The minority have a more severe form in which they develop encephalitis or meningitis basically, swelling of the brain or the lining around the brain, which can be quite severe and can cause death.

There is a pyramid of West Nile infection which looks like this: The vast majority of people infected will be asymptotic they won't have any symptoms at all. Of that group who do have symptoms, most all will have a milder form of the West Nile.

Fewer than 1 percent of all infected people will have central nervous system involvement. That's about 20 percent of the symptomatic people. What should the people who have the milder form of West Nile do, if anything?They should visit their doctor to get a diagnosis because some of these symptoms can act like other illness, too. Usually your medical caretaker will just be supportive: He or she will tell you to take care of yourself, get plenty of rest, fluids and so.

If someone is having central nervous system illness, then the issue is about alleviating pressure on the brain. Unfortunately, there's not a medication you take an antibiotic that will just make it go away. I've heard that if you have a compromised immune system, you're at greater risk. Can taking medication that will improve your immune system help?In terms of your immune system, that could be immune system suppression that some people already have in other words, it's pre-existing.

One of the big forms of immune system suppression in people is aging. That is something, of course, you can't do anything about, and those people tend to get more severe West Nile when they get infected. Talk a little about the mosquito itself.The species is called Culex Tarsalis. It's a species that feeds on birds; that's where it picks up the virus. If a bird is infected with the virus, it can pass it along to the mosquito; then in midsummer, that mosquito turns around and starts feeding on mammals instead of birds. Why?Part of the reason is that young birds start developing some behaviors where they can avoid mosquitoes by midsummer. So, it is easier for a mosquito to feed on mammals than birds. Early in the summer, those young birds aren't so good at avoiding mosquitoes, but by midsummer they can.

So the mosquitoes turn to mammals or people and if one of those infected mosquitoes feeds on us, that's who will get West Nile. Why are horses the only mammals that get severe West Nile?A lot of horses can die from West Nile virus, or it affects them so badly that they just need to be put down. Fortunately, there is a vaccine for horses.

In the past few years in which people have started vaccinating their horses, we've had a lot fewer horse cases each year. Last year in Minnesota, I think, there were a total of only 17 reported with West Nile. In comparison, in 2002 there were nearly 1,000 horses reported. Why just horses? Why not dogs or cats?Fortunately, West Nile doesn't seem to affect people's dogs or cats too badly, if at all. It's just the way this particular virus affects different animals.


There actually are several different mosquito-borne viruses in the U.S. that affect horses. Some of them even have equine in their name for example, western equine encephalitis and eastern equine encephalitis also can affect horses quite badly. That is the way the virus has evolved. Is the Culex Tarsalis the only mosquito that transmits West Nile?Here in this part of the U.S. in Minnesota and the Dakotas that is the mosquito that not only carries the virus but also bites people. There actually are other mosquito species in this area that carry the virus, but they don't tend to bite people very often. Why not?Most mosquito species are very "host specific." That means they stick to the same kind of animal to feed on. So if you have a mosquito that feeds only on birds and never bites people, then it really isn't a risk to us. When are we most at risk for bites from Culex Tarsalis mosquitoes?The Culex Tarsalis tends to feed on people starting in midsummer through to frost time. So, mid-July to September is our biggest risk period for West Nile virus.

We are in that risk period now, so it's important to be wearing mosquito repellent and long, loose clothing when you can. I know that's hard when it's 95 degrees and humid, so that's why it's important to keep that bug spray handy and use it.

Also, the mosquito species that carries West Nile virus tends to be most active at dusk and dawn. So, you don't need to be too worried about it every single moment of the day, but it's important to be wearing repellent at dusk and dawn especially in western Minnesota, such as the East Grand Forks area. Is there anything new in the area of preventing the disease?Individually, there certainly is. Individual prevention for West Nile is one of those things that is both simple and difficult. What's simple about it is that it just comes down to using a repellent, which takes only a few minutes to apply. What's difficult about it is remembering to use it every time you go out at dawn and dusk.

Keep that bug spray handy. Keep a can of it in your car or in your outbuildings, shed or porch. Take a moment to put it on.

That few minutes can save you a few weeks or a couple of months of feeling really sick. Is there anything more in the scientific area that has been learned about this mosquito?We know this is a virus that first showed up in the U.S. in 1999, and then it swept across the whole nation. It is carried to people by different mosquito species in different parts of the U.S., but it has impacted pretty much the whole country.

Right now, there's not a human vaccine for people, but there are scientists working on that and we hope that in the next few years, there will be a vaccine for people who are high-risk. Anything else happening in West Nile prevention?We monitor West Nile in the state. One other thing we monitor is what's going on with the mosquito population. In June, we had a peak in the numbers of Culex Tarsalis mosquitoes that were really higher than any other years. That worried us about the number of mosquitoes out there and their capabilities to carry disease to people. That underscored the need to use those repellents. Keep them handy. Has this unusually high number of Culex Tarsalis mosquitoes increased the number of West Nile cases?It might be a bit early in the season to know for sure. We've had two human cases in Polk and Clay counties so far.

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