This is SCIENCE IN THE NEWS in VOA Special
English. I'm Shirley Griffith.
And I'm Steve
Ember. Today, we tell about diseases
spread by mosquitoes -- the most widely hated insects in the world.
There are more than two thousand different kinds of
mosquitoes. Female mosquitoes bite people
to drink their blood. Male mosquitoes do
not drink blood. They drink fluids from
plants. The female mosquito uses its thin
sucking tube to break the skin, find blood and inject the victim with a substance that keeps blood flowing.
The female mosquito drinks the blood and uses it to
produce as many as two hundred fifty eggs. The insect leaves the eggs in any standing water.
eggs produce worm-like creatures called larvae in two days to a few
months. However, some eggs can stay in
water for years until conditions are right for development. The larvae feed on organisms in the
water. After four to ten days, they
change again, into creatures called pupas. The pupas rise to the surface of the water. Adult mosquitoes pull themselves out of the
pupas and fly away.
Health Organization says mosquitoes carry organisms that cause disease and
death for millions of people throughout the world. The most important disease spread by
mosquitoes is malaria. The W.H.O. says two
hundred forty-seven million people became infected with malaria in two thousand
six. Malaria caused almost one million
deaths, mostly among children in Africa. The disease is found in more than one
hundred countries in Africa, Asia, the western Pacific Ocean, the Middle East and
Central and South America.
Malaria parasites enter a person's blood through a
mosquito bite. These organisms travel to
the liver. They grow and divide
there. After a week or two, the
parasites invade red blood cells and reproduce thousands of times. They cause the person's body temperature to
rise. They also may destroy major
organs. People with malaria may suffer
kidney failure or loss of red blood cells.
Some medicines are generally effective in preventing
and treating malaria. They are designed
to prevent the parasites from developing in the body. People die from malaria because they are not
treated for the disease or the treatment is delayed.
World Health Organization says mosquito control efforts are improving in many
areas. But it warns that mosquitoes are
becoming increasingly resistant to pesticides, the products used to kill
This month, the W.H.O. joined with other groups to
announce a new effort against malaria. The
goal is to reduce use of the pesticide known as DDT. The United States banned most uses of DDT in
W.H.O. announced ten projects to test non-chemical methods for fighting
mosquitoes. These include trees that
repel mosquitoes and fish that eat the larvae. However, officials say any
reduction in the use of pesticides must make sure that disease control efforts
are not weakened.
Mosquitoes also carry dengue fever. The insects can survive in new and different
environments. They can spread diseases
to new areas. For example, experts say
only nine countries had dengue fever before nineteen seventy. Since then, the disease has spread to more
than one hundred countries.
World Health Organization says about fifty million people suffer from dengue
fever each year. There is no cure. Children may develop a kind of the disease
that is not serious. They may have a
high body temperature and some areas of skin may turn red.
Older adults suffer from dengue fever
much more. They may develop reddish skin
and lose their sense of taste. They also
may have pain in the head or behind their eyes. And they may experience pain in joints such as the elbow or knee. This kind of joint pain is the reason why
dengue fever is sometimes known as breakbone fever.
most severe kind of the disease is called dengue hemorrhagic fever. People who have this disease bleed from the
nose or other openings in the body. Dengue hemorrhagic fever kills about five percent of all people it
infects. The only treatment involves
controlling the bleeding and replacing lost body fluids.
Yellow fever is another disease carried by
mosquitoes. There are no effective drugs
against yellow fever. Doctors can only
hope that a person's defense system is strong enough to fight the disease. Yellow fever is found mainly in Africa, the northern
part of South America and the islands of the Caribbean Sea. The World Health Organization says there are
an estimated two hundred thousand cases of the disease and thirty thousand
deaths each year.
A virus causes yellow fever. A few days after a mosquito bite, the victim
experiences high body temperature and pain in the head or muscles. Victims also may expel food they ate. Most patients improve after three to four
fifteen percent of patients develop a more serious condition. High body temperatures return and the body
turns yellow in color. The victim bleeds
from the nose, mouth, eyes or stomach. Half the people with this condition die within ten to fourteen days.
vaccine can prevent yellow fever. Experts
say the vaccine is safe and very effective. The protection continues for at least ten years and possibly for life.
Mosquitoes also carry lymphatic filariasis, also known as elephantiasis. The disease has affected more than one hundred twenty million
people. One-third of those infected live
in India. Another third are in Africa. The others live in South Asia or islands in
the Pacific Ocean.
Mosquito bites spread the worms that
cause elephantiasis. People usually
begin to develop the disease as children. Many children never experience signs of the disease. But it may cause hidden damage to the body's
lymphatic system and kidneys.
worst signs of elephantiasis appear in adults. The signs are more common in men than in women. These include damage to the arms, legs and
reproductive organs. Two drugs are
effective in treating the disease.
disease carried by mosquitoes is encephalitis. It causes an infection or swelling of the brain. Many different viruses cause different kinds
of the disease. One virus lives
naturally in birds and horses. Mosquitoes spread it to people. Mosquitoes in several Asian countries spread a kind of encephalitis
known as Japanese encephalitis. A
vaccine can prevent this sickness.
kinds of encephalitis include West Nile, Saint Louis and Eastern Equine. Most healthy people infected with the virus
show no signs. Or they become sick for
only a day or two. But those with weak
natural defenses may develop a severe infection. They may suffer from high body temperature,
head pain, shaking and even death.
have learned many things about mosquitoes. For example, the insects can smell carbon dioxide in the breath of a
person or animal from as far away as sixty meters. Mosquitoes often like the blood of animals
better than the blood of people.
The insects also like dark colors. They do not bite women who are bleeding during
their fertility period. But they do bite pregnant women. Many kinds of mosquitoes
are most active in the early morning and early evening. They eat mostly at night.
say the best way to prevent the diseases carried by mosquitoes is not to be
bitten by one. There are several ways to
prevent mosquito bites. Do not keep
standing water anywhere near your home.
Remove all containers that could provide a place for
mosquitoes to live. Stay in an enclosed
area when mosquitoes are most active. Wear clothes that cover most of the body.
ways to prevent mosquito bites are to put anti-insect products on the skin,
clothing and sleeping areas. Also, place
nets treated with insect poison on windows and over the bed at night.
SCIENCE IN THE NEWS was written by Nancy Steinbach. Brianna Blake was our producer. I'm Steve Ember.
I'm Shirley Griffith. Join us again next
week for more news about science in Special English on the Voice of America.