The Buzz About Mosquitoes

The National Institute of Health recently released a warning of an outbreak of Japanese encephalitis, a mosquito-borne viral form of encephalitis, in Korea. Such warnings are given either when the incidence of culex mosquitoes (its primary carriers) rises, or when pigs, common mosquito hosts, show higher than normal amounts of antibodies to Japanese encephalitis. One of the best ways to safeguard yourself against encephalitis and other mosquito-borne illnesses is to learn a little more about the habits of that annoying bug known as the skeeter.

Why Do They Bite?

You've probably noticed that in summer, especially after long periods of rain, mosquitoes flourish. This is because stagnant pools of water left by the rain are perfect mosquito incubation grounds.

"In an warm, humid environment, mosquito eggs mature quickly, which causes an explosion in the number of mosquitoes," said Han Tae-hee, a malaria researcher at Inje University. He explained that with every rise in temperature of 10 degrees centigrade, the number of mosquitoes doubles.

Most of the mosquitoes trying to nibble on you are females in the breeding season. Those females need more animal protein than usual to produce the eggs inside them. Most female mosquitoes survive only two or three weeks after laying their eggs, but they need blood for this. If they haven't found blood, they can live for months until they do.

What Do They Spread?

The most common illnesses spread by mosquitoes are malaria (hakjil in Korean) and Japanese encephalitis (noe-yeom). There are 17 areas in Korea in which malaria is known to be prevalent, including Ilsan, Deokyang, Paju, Inchon and Ongjin in Kyonggi province, and Cheolwon and Hwacheon in Kangwon province. This year, however, a downturn in the figures for malaria infection appears to signal a reverse in a trend which has seen infections figures swell over the past few years. Up until mid-July, 736 people were infected.

Japanese encephalitis infection rates have also declined, due to the precautions taken against the spread of the disease, such as widespread vaccination and maintenance of clean surroundings.

Lee Jong-gu of the National Institute of Health explained, "The vaccination against Japanese encephalitis is effective for about five years. Children who were vaccinated at 12 to 24 months old should have repeat injections at 6 and then 12 years old. Vaccines are only effective after a month from injection, so in the meantime other precautions should always be taken."

What Can You Do?

If you don't want to advertise yourself as a free lunch for skeeters, try not to smell of the things that they like. Mosquitoes are often attracted by things which we might deem unpleasant, such as sweat and smelly feet, but also by perfumes and skin lotions. It is therefore advisable to keep your body clean and smell-free by washing frequently. At night, sleep away from the walls, as mosquitoes tend to hide against them, and consider using a bed net.

Koreans commonly burn "smudge" fires － smoldering masses of vegetation － outside the house to draw mosquitoes out of the house. The fires work because the smoke contains carbon dioxide, which mosquitoes are attracted to.

Another way to exterminate these blood-suckers is to use an electronic mosquito repellent. These also attract mosquitoes with carbon dioxide and then kill them off with insecticide. Of the two most popular plug-in types, one comes as a solid mat and the other as a liquid. An older type of repellent, an aerosol containing insecticide, is now less popular due to environmental concerns. The latest models repel females by mimicking the sounds of male mosquitoes by generating supersonic waves of over 12,000 hertz. Fertilized female mosquitos avoid male mosquitos.

What Do They Like?

"When a mosquito is searching for an object to bite, it relies most heavily on its sense of smell," said Im Chae-seung, a medical professor at Korea University. "A mosquito can smell the carbon dioxide in human breath at a distance of 10 to 20 meters." It can detect smells of secretions from human skin such as amino acids, lactic acid and ammonia at an even farther distance.

Mosquitoes are also good at sensing different colors. It particularly likes natural colors such as green, blue, violet and black, which have short wavelengths. Its numerous sensors can easily perceive a moving object.

Preventive Measures

- Protect children with vaccinations.

- Use mosquito repellents indoors and outdoors.

- Keep your house clean and free of pools of water.

- Avoid direct sunlight and chronic fatigue.

- Wear a long-sleeve shirt and long pants if you are out later than sunset in a malaria-prevalent area.

- Disinfect areas around cattle sheds and puddles.

Provided by Im Chae-seung,

Korea University

by Koh Jong-hwan