Malaria
Malaria, debilitating infectious disease characterized by chills, shaking, and periodic bouts of intense fever. Caused by single-celled parasites of the genus Plasmodium, malaria is transmitted from person to person by the bite of female mosquitoes.
Malaria in humans is caused by four species of Plasmodium parasites. Plasmodium falciparum is the most common species in tropical areas and is transmitted primarily during the rainy season. This species is the most dangerous, accounting for half of all clinical cases of malaria and 90 percent of deaths from the disease. Plasmodium vivax is the most widely distributed parasite, existing in temperate as well as tropical climates. Plasmodium malariae can also be found in temperate and tropical climates but is less common than Plasmodium vivax. Plasmodium ovale is a relatively rare parasite, restricted to tropical climates and found primarily in eastern Africa.
The fever that characterizes malaria develops when merozoites invade and destroy red blood cells. The destruction of red blood cells spills wastes, toxins, and other debris into the blood. The body responds by producing fever, an immune response that speeds up other immune defenses to fight the foreign invaders in the blood. The fever usually occurs in intermittent episodes. An episode begins with sudden, violent chills, soon followed by an intense fever and then profuse sweating that brings the patient’s temperature down again. Upon initial infection with the malaria parasite, the episodes of fever frequently last 12 hours and usually leave an individual exhausted and bedridden. Repeated infections with the malaria parasite can lead to severe anemia, a decrease in the concentration of red blood cells in the bloodstream. The malaria parasite consumes or renders unusable the proteins and other vital components of the patient’s red cells.
Malaria is difficult to diagnose based on symptoms alone. This is because the intermittent fever and other symptoms can be quite variable and could be caused by other illnesses. A diagnosis of malaria is usually made by examining a sample of the patient’s blood under the microscope to detect malaria parasites in red blood cells. The different species of Plasmodium can be distinguished by their appearance under the microscope. Parasites can be difficult to detect in the early stages of malaria, in cases of chronic infections, or in Plasmodium falciparum infections because often in these cases, not many parasites are present. Recent advances have made it possible to detect proteins or genetic material of Plasmodium parasites in a patient’s blood.
Malaria is treated with drugs that block the growth of the Plasmodium parasite but do not harm the patient. Some drugs interfere with the parasite’s metabolism of food, while others prevent the parasite from reproducing. Drugs that interfere with the parasite’s metabolism are related to quinine, the first known antimalarial drug. Quinine is a chemical derived from the bark of the South American cinchona tree and was used as a fever remedy by the ancient Inca in the 15th century. This drug has a bitter taste and produces severe side effects, such as nausea, headache, ringing in the ears, temporary hearing loss, and blurred vision, and large doses can be fatal. However, quinine is still sometimes used in treating malaria today, particularly in developing nations, because it is inexpensive and effective.
Malaria in humans is caused by four species of Plasmodium parasites. Plasmodium falciparum is the most common species in tropical areas and is transmitted primarily during the rainy season. This species is the most dangerous, accounting for half of all clinical cases of malaria and 90 percent of deaths from the disease. Plasmodium vivax is the most widely distributed parasite, existing in temperate as well as tropical climates. Plasmodium malariae can also be found in temperate and tropical climates but is less common than Plasmodium vivax. Plasmodium ovale is a relatively rare parasite, restricted to tropical climates and found primarily in eastern Africa.
The fever that characterizes malaria develops when merozoites invade and destroy red blood cells. The destruction of red blood cells spills wastes, toxins, and other debris into the blood. The body responds by producing fever, an immune response that speeds up other immune defenses to fight the foreign invaders in the blood. The fever usually occurs in intermittent episodes. An episode begins with sudden, violent chills, soon followed by an intense fever and then profuse sweating that brings the patient’s temperature down again. Upon initial infection with the malaria parasite, the episodes of fever frequently last 12 hours and usually leave an individual exhausted and bedridden. Repeated infections with the malaria parasite can lead to severe anemia, a decrease in the concentration of red blood cells in the bloodstream. The malaria parasite consumes or renders unusable the proteins and other vital components of the patient’s red cells.
Malaria is difficult to diagnose based on symptoms alone. This is because the intermittent fever and other symptoms can be quite variable and could be caused by other illnesses. A diagnosis of malaria is usually made by examining a sample of the patient’s blood under the microscope to detect malaria parasites in red blood cells. The different species of Plasmodium can be distinguished by their appearance under the microscope. Parasites can be difficult to detect in the early stages of malaria, in cases of chronic infections, or in Plasmodium falciparum infections because often in these cases, not many parasites are present. Recent advances have made it possible to detect proteins or genetic material of Plasmodium parasites in a patient’s blood.
Malaria is treated with drugs that block the growth of the Plasmodium parasite but do not harm the patient. Some drugs interfere with the parasite’s metabolism of food, while others prevent the parasite from reproducing. Drugs that interfere with the parasite’s metabolism are related to quinine, the first known antimalarial drug. Quinine is a chemical derived from the bark of the South American cinchona tree and was used as a fever remedy by the ancient Inca in the 15th century. This drug has a bitter taste and produces severe side effects, such as nausea, headache, ringing in the ears, temporary hearing loss, and blurred vision, and large doses can be fatal. However, quinine is still sometimes used in treating malaria today, particularly in developing nations, because it is inexpensive and effective.
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