& Joannie Dobbs Wednesday,
Dengue-fever mosquitoes love daylight, dark
In Hawaii, most of us consider mosquitoes an unavoidable annoyance, but not the serious health problem they are in countries where they may transmit deadly diseases, such as malaria, yellow fever, dengue, encephalitis and West Nile virus.
But last week, Hawaii was put on mosquito alert with 48 confirmed cases of dengue fever. During 1997 and 1998, the Centers for Disease Control reported only 143 cases of dengue fever in the whole United States .
Hawaii had a dengue fever outbreak in the 1940s. So, though the current situation is unusual for Hawaii , it has happened before.
For most adults, dengue fever, and the more severe dengue hemorrhagic fever, has symptoms similar to the flu -- high fever, severe headaches and extreme body and joint pain. It also can cause vomiting, eye pain and rash.
Children, surprisingly, may show little or no outward symptoms of dengue fever. In fact, as many as 85 percent of children exposed to the virus show no symptoms.
Like the flu, treatment of dengue includes replacing the loss of water, sodium and potassium with fluids, such as Gatorade, salted soups and orange juice.
But there are no magical medications. In fact, if you contract dengue, it is important to avoid certain medications. To prevent possible bleeding complications, do not take aspirin or ibuprofen or high levels of vitamin E. If you see signs of abnormal bleeding or use any type of blood thinner, see your physician at once.
Knowing how to prevent dengue fever is far better than knowing the best way to treat it. Understanding some basic mosquito biology and what factors attract mosquitoes can help you avoid becoming a mosquito meal.
The transmission of dengue fever in Hawaii is thought to be by the mosquito species Aedes albopictus. This species is most active from daybreak until dusk and is attracted to dark-colored clothing.
Since mosquitoes are a worldwide problem, millions of dollars have been spent on research about how to repel these blood-thirsty "little flies," as the Portuguese used to refer to them.
Here are some facts: Mosquitoes are very attracted to carbon dioxide (in the air we exhale) and lactic acid produced naturally by the body. Since these two metabolic compounds are essential to life, mosquitoes are attracted to most live humans.
Recently, research also has shown that mosquitoes are attracted or repelled by more than 300 metabolic chemical compounds we produce just to stay alive.
The most effective repellents typically contain DEET, N,N-diethylmetatoluamide. Because of the potential toxic effects of DEET, directions for use should be followed closely.
A number of foods and diets are touted to repel mosquitoes, but none has been proven to work.
With regard to plants and plant extracts, concentrated citronella in some products has been shown to repel mosquitoes, whereas simply planting citronella didn't appear to have a significant effect. Also, there is some evidence that peppermint oil repels mosquitoes.
The greatest hope for an effective mosquito repellent may come from a plant loved by our feline friends. Researchers from Iowa State University reported at this year's American Chemical Society meeting that a compound contained in catnip (nepetalactone) is 10 times more effective in repelling mosquitoes than DEET. Although nepetalactone has not been tested on animals or humans, this catnip compound shows great promise. If it proves safe and effective, we may have to learn how to share with our cats.
Alan Titchenal, Ph.D., C.N.S. and Joannie Dobbs, Ph.D., C.N.S.
are nutritionists in the Department of Human Nutrition, Food and Animal Sciences,
College of Tropical Agriculture and Human Resources, UH-Manoa.
Dr. Dobbs also works with the University Health Service
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