Malaria
Malaria is infection of red blood cells with the single-celled parasite Plasmodium, which causes fever, an enlarged spleen, and anemia.
Malaria is usually spread by the bite of an infected female mosquito. Very rarely, the disease is transmitted through a transfusion of contaminated blood or an injection with a needle that was previously used by a person with malaria. Four species of malaria parasites--Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale, and Plasmodium malariae--can infect people.
Although drugs and insecticides have made malaria rare in the United States and in most developed countries, the disease remains common and deadly in tropical areas worldwide. There are 300 to 500 million people infected with malaria, and 1 to 2 million deaths occur each year. Most of these deaths occur in children younger than 5 years of age. Visitors from the tropics or travelers returning from tropical areas can bring the infection with them.
The cycle of malarial infection begins when a female mosquito bites a person with malaria. The mosquito ingests blood that contains malarial parasites. Once inside the mosquito, the parasite multiplies and migrates to the mosquito's salivary gland. When the mosquito bites another person, the parasites are injected along with the mosquito's saliva. Inside the person, the parasites move to the liver and multiply again. They typically mature over an average of 1 to 3 weeks, then leave the liver and invade the person's red blood cells. The parasites multiply yet again inside the red blood cells, eventually causing the infected cells to rupture.
Plasmodium vivax and Plasmodium ovale can remain in the liver in a dormant form that periodically releases mature parasites into the bloodstream, causing recurring attacks of symptoms. Plasmodium falciparum and Plasmodium malariae do not persist in the liver. However, mature forms of Plasmodium malariae can persist in the bloodstream for months or even years before causing an attack of symptoms.
Symptoms and Complications
As the infected red blood cells rupture and release parasites, a person suddenly develops a shaking chill followed by a fever that can exceed 104° F. Headache, body aches, and nausea are common. The fever typically falls after several hours, and heavy sweating occurs. Fevers eventually become periodic, occurring at 48-hour intervals with Plasmodium vivax and Plasmodium ovale and at 72-hour intervals with Plasmodium malariae. The fevers caused by Plasmodium falciparum are often not periodic, but sometimes occur at 48-hour intervals. Travelers who acquire malaria usually develop symptoms within the first few months after their return, although it may take more than a year for symptoms to develop.
As the illness progresses, the spleen enlarges. A decrease in the level of sugar (glucose) in the blood can occur in people infected with Plasmodium falciparum and may be severe in people who have a large number of parasites in their blood--particularly if they are treated with the drug quinine.
Falciparum malaria, caused by Plasmodium falciparum, is the most dangerous form of malaria and can be fatal. In falciparum malaria, the infected red blood cells often stick to the walls of small blood vessels and clog them, resulting in damage to many organs--particularly the brain (cerebral malaria), lungs, and kidneys. Cerebral malaria is a particularly dangerous complication that can produce high fever, headache, drowsiness, delirium, confusion, seizure, and coma. It most commonly occurs in infants or young children, pregnant women, and people who travel to high-risk areas. In falciparum malaria, fluid can accumulate in the lungs and cause severe breathing problems. Damage to multiple organs can cause a fall in blood pressure.
Blackwater fever is an uncommon complication of falciparum malaria. It is caused by the rupture of large numbers of red blood cells, which releases blood pigment (hemoglobin) into the bloodstream. The released hemoglobin is excreted in the urine, which turns the urine dark. Kidney damage may be severe enough to require dialysis. Blackwater fever is more likely to develop in people who have taken quinine for treatment.
Malaria caused by Plasmodium vivax, Plasmodium ovale, and Plasmodium malariae tends to be less severe, although these parasites can remain in the blood for long periods, producing fever, chills, headache, poor appetite, fatigue, and a general feeling of illness (malaise).
Diagnosis
A doctor suspects malaria when a person develops fever and accompanying symptoms during or after traveling to an area where malaria is present. Periodic fever develops in less than half of American travelers with malaria, but when present, suggests the diagnosis. Identification of parasites in a blood sample confirms the diagnosis. More than one sample may be needed. The laboratory identifies the species of Plasmodium found in the sample, because the treatment, complications, and prognosis vary depending on the species involved. Plasmodium falciparum infection is an emergency and requires immediate evaluation and treatment.
Prevention and Treatment
Mosquito control measures, which include eliminating breeding areas and killing larvae in the standing water where they live, are very important. People who live in or travel to malaria-infested areas can also take precautions to limit mosquito exposure, such as using insecticide sprays in homes and outbuildings, placing screens on doors and windows, using permethrin-impregnated mosquito netting over beds, and applying mosquito repellents containing DEET on exposed areas of the skin. People can wear long pants and long-sleeved shirts, particularly between dusk and dawn, to protect against mosquito bites. People subject to intense mosquito exposure can spray permethrin on their clothing before it is worn.
Vaccines for preventing malaria are still in the experimental stage.
Drugs should be taken to prevent malaria during travel in areas where malaria is prevalent. The preventive drug is started before travel begins, continued throughout the stay, and extended for a period of time that varies for each drug but is usually 4 weeks after the person leaves the high-risk area.
Many drugs are used to prevent and treat malaria. Drug resistance is a serious problem, particularly with the dangerous Plasmodium falciparum species. The prevalence of drug-resistant strains varies in different parts of the world. Thus, the choice of drug for prevention varies by geographic location. Information about specific sites is available from the Centers for Disease Control and Prevention. The choice of drug for treatment is based on the infecting species of Plasmodium and its known or suspected sensitivities.
Chloroquine is the preferred drug for prevention of malaria caused by Plasmodium falciparum in Mexico, areas of Central America west of the Panama Canal, Haiti, the Dominican Republic, and some areas of the Middle East. Strains of Plasmodium falciparum that are resistant to chloroquine are present in most other areas of the world where malaria occurs. In those areas, the recommended preventive drugs include mefloquine, doxycycline, or the combination atovaquone-proguanil.
Chloroquine is the drug of choice for treatment in a person who has malaria caused by Plasmodium vivax, Plasmodium ovale, or Plasmodium malariae--except in a very few areas where resistance to chloroquine in people with Plasmodium vivax has been reported. Chloroquine also is acceptable for Plasmodium falciparum infections acquired in areas without known drug resistance. Primaquine is added to kill persistent parasites in the liver of a person infected with Plasmodium vivax or Plasmodium ovale. Before primaquine is given, a blood test is done to look for a relatively common enzyme deficiency (G6PD deficiency). People with G6PD deficiency who are given primaquine may have a breakdown of their red blood cells.
Falciparum malaria in areas with known chloroquine resistance is treated with quinine plus doxycycline or, if uncomplicated, atovaquone-proguanil. Atovaquone-proguanil has fewer side effects than quinine. Mefloquine can be used but side effects are common. If the person cannot take drugs by mouth, quinidine may be given intravenously under careful observation in the hospital.
Travelers who develop a fever while in areas where malaria is prevalent should be examined by a doctor immediately. If medical care is not available, self-treatment for presumed malaria is sometimes recommended with pyrimethamine-sulfadoxine or atovaquone-proguanil until medical evaluation is possible. This approach should be discussed with a doctor before traveling.
Chloroquine is relatively safe and is approved for use in children and pregnant women. Mefloquine sometimes causes nausea, dizziness, and trouble sleeping. It may rarely produce seizures or psychiatric problems. It should also be avoided in people with certain heart conditions. Quinine is often associated with headache, nausea, vomiting, visual disturbances, and ringing in the ears--a condition known as cinchonism. Quinine may also cause low blood sugar in people infected with Plasmodium falciparum. Atovaquone-proguanil may cause nausea, vomiting, or abdominal pain and is not used in people with poor kidney function, pregnant women, or infants.
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