MOSQUITO:
GETTING TO KNOW THE ENEMY
Read the passage.
Nearly two million species
of insects, grouped into about 30 orders,
live in many different habitats throughout the world. They are very important because they
pollinate flowers and are food for birds
and other animals. However, many insects are
pests that feed on crops or
spread diseases. One such insect is the mosquito.
There are about 3, 000 species of
mosquitoes, which are distinguished by their antennae of
14 or 15 segments and by the presence
of scales on the veins
of theirs wings. The larvae are
called wigglers and aquatic, feeding on plants,
algae, and microscopic animal
life. Some mosquitoes feed on
the juices of plants, and some does not feed at all in
their adult stage. Only female mosquitoes
suck the blood of humans and other warm-blooded
animals, because they need blood to develop each batch
of fertile eggs. But like the male mosquito, females
feed only on nectar for their food source.
The female mosquito locates her
human targets by following the carbon dioxide that
we exhale. When the mosquito bites a
human, she injects saliva into our skin
before drawing blood. This
saliva helps her to penetrate the skin and prevents blood clots
from developing in her food canal. The welts and
itching that we experience after being bitten are
an allergic reaction to
the saliva.
Few people like mosquitoes. They inflict itchy bites and buzz around our
ears. But mosquitoes are much more than
a nuisance, they can pose serious health
hazards. Insects that feed on
blood have the potential to transmit diseases
between humans and between animals and humans.
Mosquitoes are the most highly developed insect bloodsuckers and
are carriers of several serious diseases,
namely yellow fever, encephalitis,
dengue fever, and malaria.
ENCEPHALITIS
Viral encephalitis
is a disease transmitted by mosquitoes from infected small animals, usually
birds and rodents, to humans. It is a disease that causes inflammation
of the brain, and the risk of getting the
disease is highest during warm months
when birds and mosquitoes reproduce.
There are several types of mosquito-borne
encephalitis that infect people. Although
most people infected with viral encephalitis have only mild
or no symptoms, serious cases
can cause headaches, high fevers,
lethargy, convulsions,
delirium, coma,
and even death. Symptoms appear 4 to 15 days after being
bitten.
Treatment
There is no special treatment
available for this disease. Medical care is
aimed at managing the symptoms and complications that the
disease causes.
Prevention
During the mosquito season,
people should take the following precautions:
wear protective clothing between
dusk and dawn;
apply mosquito repellent
to skin and clothing; having screens on all windows
and doors; drain or cover all standing
water; use mosquito netting to cover
sleeping infants.
DENGUE FEVER
Dengue fever is
a viral disease carried by the Aedes mosquitoes. The disease occurs mainly in tropical
and subtropical regions and
is most common during the rainy
season in areas infected
with the infected mosquitoes. According
to the WHO, 2.5 billion people at risk
from the four major types of dengue
virus, which is transmitted to people from infected mosquitoes. Each year there are tens of millions
of cases.
Symptoms of dengue fever generally
start 5 to 6 days after being bitten by the infected mosquito and include fever,
painful headaches, eye, joint,
and muscle pain,
and rash. The rash
usually begins on the arms or legs about 3 to 4 days after the fever
starts. These symptoms resolve
completely within 1 to 2 weeks. Dengue
haemorrhagic fever is a severe,
potentially fatal infection that
occurs when someone with immunity to one type of
dengue virus is infected by a different type.
Its symptoms include loss of appetite,
vomiting, intense abdominal
pain, shock and bleeding from the nose
or under the skin. The occurrence
of dengue haemorrhagic fever may be
associated with those either experiencing their second
infection, being immune-suppressed, or being under
the age of 15.
Treatment
There is no vaccine against
dengue fever. Recommended treatment
for the disease is bed rest and
common drugstore pain and fever medication. Since there are four types of dengue viruses,
having one types of virus will give protection against
that type, not the others. Dengue
haemorrhagic can be fatal. Early medical
intervention for dengue haemorrhagic fever may prevent
serious illness.
Prevention
Because Aedes mosquitoes are
usually most active during early morning
hours just after daybreak and late afternoon
hours, it is wise to avoid exposure during
these times. Also, using netting and
screens, mosquito repellent, and protective clothing will reduce exposure
to mosquito bites.
MALARIA
Malaria is
a tropical disease caused by protozoal parasites. It is spread by only 60 of the 380 species of
the Anopheline mosquito, especially during rainy seasons. Malaria annually affects from 300 to 500
million people worldwide, and causes more than one million deaths.
Symptoms may occur in 6-8 days or several months after being bitten and include
regularly occurring fevers with chills, nausea,
and muscle pain.
Infection results in the enlargement
of the spleen and liver,
and in fatal cases, capillaries in
the brain are blocked.
The majority of malaria deaths occur
among young children and pregnant women.
Treatment
Early diagnosis and prompt
adequate treatment is essential in curing malaria and preventing death. A
limited number of drugs for treating malaria are available. However, in some regions the parasites are
resistant to certain antimalarial drugs, particularly chloroquine. People continuously infected gradually
develop immunity to the disease.
Prevention
Preventing malaria includes a variety
of measures: wearing protective
clothing, using repellents, and sleeping under bed nets treated
with insecticides. Community
protection measures, like using insecticides, are directed against
the mosquito to control transmitting the disease. But, Bacillus
thuringiensisisraelensis (Bti) – naturally occurring bacterium
that is lethal to mosquitoes and black
flies – may be a solution because mosquitoes are becoming
more resistant to chemical insecticides, which have been used for decades
to control malaria. The importance
of Bti is that it is an environmentally safe biological pesticide
found in nature.
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