MOSQUITO: GETTING TO KNOW THE ENEMY (UNIT 11)

UNIT 11

 

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 their wings. The larvae are called wigglers and are aquatic, feeding on plants, algae, and microscopic animal life. Some mosquitoes feed on the juices of plants, and some do 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 very 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 cause 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; have 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 infested with the infected mosquitoes. According to the WHO, 2.5 billion people are 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 hemorrhagic 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 hemorrhagic 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 type of virus will only give protection against that type, not the others. Dengue hemorrhagic can be fatal. Early medical intervention for dengue hemorrhagic 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 cutting 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

Prevention 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 thuringiensis israelensis (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.