This is Bob Doughty. And this is Sarah Long with SCIENCE IN THE NEWS, a VOA Special English program about recent developments in Science. Today, we tell about malaria, a disease that affects millions of people around the world.
Malaria is a common and serious disease that has affected people for thousands of years. Today, it continues to be a major public health problem throughout the world. It is most common in developing countries, especially in Africa, Asia, and Central and South America.
The World Health Organization estimates that as many as five-hundred-million cases of malaria develop each year. More than one-million people die from the disease each year. Most of them are children in African countries.
Malaria is spread by a common insect, the mosquito. The Anopheles mosquito carries the parasite that causes the disease. Very small parasites develop in the stomach of the mosquito. Parasites are organisms that live on or in another animal and get their food from that animal.
The general name for the malaria parasite is Plasmodium. Mosquitoes pass the parasites to people when they drink blood through the skin. However, only the female Anopheles mosquitoes drink blood. The male Anopheles mosquitoes feed only on plant juices.
The female Anopheles mosquito drinks blood from humans and animals by breaking through the skin with its long, tube-like feeding device. The parasites enter the victim's blood. The blood carries the parasites to the victim's liver. From there they invade cells and reproduce.
After nine to sixteen days, the parasites return to the blood and enter the red blood cells. Then they reproduce again. As they do this they destroy the blood cells. In a short time, the victim develops a high body temperature. The victim becomes weak and is unable to carry out normal activities. Other signs of malaria include pain in the muscles, headache, chills and shaking. Patients with severe malaria may develop liver and kidney failure, seizures and coma.
These signs of malaria have been observed since the beginning of history. Researchers studying bodies of ancient Egyptians have found evidence of the disease in people who lived at least three-thousand years ago. And scientists have found mosquitoes in fossil remains millions of years old. However, the real cause of the disease was unknown to ancient peoples.
At one time, it was believed that malaria was caused by bad air. People believed this bad air came from areas of water that were not deep and did not move. It seemed that malaria was most common near these swamps.
Ancient people suspected that mosquitoes were linked to the spread of malaria. Greek historian Herodotus lived about two-thousand-four-hundred years ago. He noted that in swampy areas of Egypt, some people slept in tall structures where mosquitoes could not go. Or they slept under special material called nets that mosquitoes could not go through.
In Eighteen-Seventy-Six, British scientist Patrick Manson discovered that mosquitoes were responsible for passing the disease to humans. More exactly, he discovered that insects carry the parasites and pass them to humans.
In Eighteen-Eighty, French doctor Alphonse Laveran discovered that the Plasmodium parasite causes the disease. In Eighteen-Ninety-Seven, a British scientist, Ronald Ross, found the malaria parasite in the Anopheles mosquito.
For his discovery of the cause of malaria and other scientific work, Doctor Laveran received the Nobel Prize for Medicine in Nineteen-Oh-Seven. Mr. Ross received the Nobel Prize for Medicine in Nineteen-Oh-Two for his work on malaria.
The discoveries of the three scientists soon led to efforts to control malaria. Then, the discovery of the insect poison D-D-T led to efforts to try to end the disease completely.
Between Nineteen-Fifty-Five and Nineteen-Sixty-Nine, the World Health Organization's Global Malaria Eradication Program carried out a series of campaigns against the disease. The goal was to use chemicals to kill mosquitoes inside homes around the world. The effort was successful in large areas of North America, southern Europe, the former Soviet Union and some parts of Asia and South America. The spread of the disease in these areas was halted.
However, the disease continued in Central America, some parts of South America, and most Asian countries. The W-H-O program never was attempted in Africa. This is because it was too difficult and costly for most African countries.
In Nineteen-Sixty-Eight, malaria suddenly spread rapidly among people in Sri Lanka, where it was believed the disease no longer existed. The disease also spread in Central America and Southeast Asian countries, as well as in parts of Africa.
Efforts to end malaria throughout the world were suspended in Nineteen-Sixty-Nine. Today, the W-H-O says that malaria control programs must be developed for local areas. It says such programs must involve everyone in each community – citizens, health experts and people involved in development.
There are four different kinds of malaria. They are caused by four different kinds of parasites. Three kinds of parasites cause victims to suffer high body temperatures, or fevers, every few days. But they do not cause death. However, the most common malaria parasite also is the most dangerous. This parasite causes infections that can lead to death.
The best way to prevent malaria is to avoid the mosquitoes that carry the malaria parasites.
The female Anopheles mosquito takes blood from its victims mainly at night.
So, people can place special nets treated with insect poison over their beds at night while they sleep. People can also put anti-insect chemicals on their skin, on clothing and in sleeping areas. They also can wear clothes that cover most of the body.
If the mosquitoes get past barriers used to block them, drugs are necessary for treatment. Drugs can destroy the malaria parasite as soon as it enters the human body. This prevents the parasites from entering the red blood cells and dividing. Some drugs can prevent the parasite from establishing itself in the liver. However, malaria must be treated early for the treatment to be effective.
Well before the fifteenth century, people in what is now Peru knew that the covering or bark from the cinchona tree was effective in treating the signs of malaria. In Eighteen-Twenty, two French researchers identified the substance in the bark as quinine. Until the twentieth century, quinine was the chief drug used to prevent and cure some forms of malaria. Today, manufactured drugs are mostly effective in treating the disease. These drugs are designed to prevent the parasites from developing in the body and causing malaria.
The most commonly used malaria prevention drug is chloroquine. It is suggested for use in Mexico, Central America, Haiti, the Dominican Republic, and the Middle East. Another drug, called mefloquine, is used in all other areas of the world where malaria is a threat. Both drugs must be taken once a week on the same day each week. Another commonly used anti-malaria drug is doxycycline. It must be taken every day.
Although these drugs are effective in preventing malaria, great numbers of people still die every year from the disease. In almost all cases, this is because of delayed treatment or no treatment at all. International health organizations are increasing efforts to reduce the deaths from malaria in the next ten years.
This SCIENCE IN THE NEWS program was written by Oliver Chanler. It was produced by George Grow. This is Bob Doughty. And this is Sarah Long. Join us again next week for more news about science in Special English on the Voice of America.