Today, mosquitoes continue to threaten man in many ways. Two of the diseases they cause - malaria and dengue - affect more than 80 countries.



There are 160 different species of mosquitoes in the United States but not all of them bite. Only the female of the species does since the eggs she carries require blood. These eggs are usually laid in water and hatch within a few days.

Adult mosquitoes are three to five millimeters long, have one pair of wings, and live for 10 to 14 days or months. They live longer in cold weather.

Worldwide, the three types of mosquitoes that often cause trouble are the Anopheles stephensi, Aedes aegypti, and Culex pipiens quinquefasciatus. They transmit diseases by picking up germs from infected animals or people and bringing these to others whenever they suck blood.

"Anopheles breeds in fresh as well as polluted waters, particularly in the edges of ponds and streams, in pools, water-filled receptacles, and puddles. Aedes breeds in anything holding clean or filthy water. This includes flower vases, animal drinking pans, old tires, and other places where water is trapped. Culex breeds in polluted water and in drains, latrines, and sometimes in rain water collected in roadside ditches," said the editors of "Health Alert", a publication of the Health Action Information Network.

Mosquitoes have different biting habits. The Anopheles and Culex are nocturnal creatures and bite only at night. Aedes is a day-biting species which is active two hours after sunrise and two hours before sunset.

Regardless of which species bites you, mosquitoes are a threat to health. Below are some of the diseases they cause, their symptoms and complications.

Malaria remains a problem in 82 countries despite efforts of the World Health Organization to control the disease. Every 30 seconds, one person dies of malaria while more than 100 million people or 40 percent of the world's population get the disease each year. There are 1,000 new cases reported annually in America alone.

In the old days, people thought malaria was caused by bad air which is how the disease got its name. Now we know that mosquitoes are to blame. They carry the spore of the malaria parasite Plasmodium in their saliva and transfer this to the people they bite.

Once inside the victim's body, the spore goes to the liver and reproduces in the red blood cells. After a while, the infected cells burst, scattering new malaria parasites that attack other cells.

There are four types of malaria depending on the species of Plasmodium which infects a person. All of them cause headache, pain in the limbs, sweating, and chills which last for 15 minutes to an hour. These symptoms begin anywhere from eight days to eight months after the victim is bitten.

The most severe form is falciparum malaria or cerebral malaria which can be fatal if treatment is delayed or inadequate. In this type, the parasites attack the brain and nervous system, and may cause sudden death. (Next: More diseases from mosquitoes.)

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