Malaria Overview


Suppose you're on a summer vacation in Southern Florida watching the sun set, and the mosquitoes are buzzing. You may suffer a few bites and be uncomfortable with the itchy welts. But if you're a mother in tropical Africa, a biting mosquito is one of your worst fears, because it can transmit malaria. In this article, we'll learn about this serious, often fatal disease and find out why it's one of the world's most pressing public health concerns.

Malaria is an infection transmitted by a certain type of mosquito. Eradicated in the United States and other developed countries, it is now a disease of tropical areas in Africa, Asia, Central and South America, the Middle East and Oceania. Today, malaria is widespread in more than 100 countries, affecting about 300 million people and causing 1 million deaths a year. More than 90 percent of cases occur in tropical Africa, with young children and pregnant women making up most cases. In Africa, malaria is the leading cause of death for children under the age of five.

Globally, more than 2 billion people are at risk for malaria, with the majority of cases occurring among the poorest 20 percent of the world's population. In these poor and often rural areas, healthcare systems are inadequate and sanitation is poor. Increasing resistance to the drugs used to treat malaria and insecticides used to prevent it also contribute to the growing prevalence of the disease and to its resurgence in areas where it had been eliminated.

Source:Roll Back Malaria Partnership

map of malaria outbreaks worldwide
Photo courtesy CDC
The geographic distribution of malaria

Causes of Malaria
Malaria is caused by parasitic, single-celled organisms called Plasmodium. Like the Avian flu, malaria is a vector disease, in which the infecting organism is transported by an intermediary animal carrier. In the case of malaria, the disease is transmitted by mosquitoes -- but only by female mosquitoes of the Anopheles genus.

a mosquito
Photo courtesy Jim Gathany/CDC
A female mosquito (Anopheles gambiae), feeding
There are four types of malaria: Plasmodium vivax, Plasmodium falciparum, Plasmodium malariae, and Plasmodium ovale. P. vivax and P. falciparum are the most common types. P. falciparum, found throughout tropical Africa, Asia and Latin America, is the most deadly type.

The mosquito picks up the parasite when it bites and extracts blood from infected people. The parasites reproduce while the mosquito uses the blood to nurture her eggs. When the mosquito bites a human again, the parasites are passed into that person's blood. Once inside the body, the parasites multiply rapidly in the liver and in red blood cells. From there, the parasites may invade other organs, including the brain.

Malaria can be transmitted from human to human by transfusion of infected blood and by contaminated syringes and needles. In areas where the disease is common, people are infected so frequently that they develop a degree of acquired immunity and have no symptoms. They may unknowingly spread the disease through blood. Pregnant women can also pass the parasites during pregnancy or birth.

We'll learn about the symptoms, diagnosis, treatment and prevention of malaria in the next section.

Malaria in the United States?
Malaria was eradicated in the United States in the early 1950s. Immigrants and returning travelers can reintroduce the disease, since the Anopheles mosquito is found throughout much of America. The disease could be spread by local mosquitoes biting an infected person and then biting other people [Source: Centers for Disease Control and Prevention].

Malaria: From Symptoms to Prevention

Malaria symptoms can range from none to very mild in uncomplicated disease. The flu-like symptoms are caused by toxins released when red blood cells rupture and the parasites move on to infect other cells.

In severe malaria, infections are complicated by metabolism or blood abnormalities and by serious organ failures, and may result in death. The incubation period -- the time between the onset of the infection and the appearance of symptoms -- is usually between nine and 30 days, depending on the type of parasite. In some types of infections, symptoms may not emerge for months.

Malaria Symptoms
Uncomplicated Malaria
Complicated
Malaria
Bouts of fever
Cerebral malaria, with abnormal behavior, impairment of consciousness, seizures, coma or other neurological abnormalities
Chills
Severe anemia
Sweats
Hemoglobin in the urine
Headaches
Fluid in the lungs (pulmonary edema)
Nausea and vomiting
Acute respiratory distress syndrome (ARDS)
Slight diarrhea
Blood coagulation abnormalities
Body aches
Cardiovascular collapse and shock
General malaise

Sources: CDC, Roll Back Malaria Partnership

Diagnosis
While malaria may be suspected based on a patient's symptoms, a definitive diagnosis requires laboratory tests to identify the parasites or their components. The preferred and most reliable method for diagnosing malaria is to examine a drop of blood under a microscope. Staining of the blood and spreading the sample out as a smear on a slide allows the parasites to be easily visualized, and each of the four types has distinguishing characteristics.


Photo courtesy Dr. Mae Melvin/CDC
A photomicrograph of a blood smear showing red blood cells that contain developing P. vivax parasites, magnified 1000 times.

Rapid Diagnostic Tests (RDTs) offer an alternative when microscopy is not available. RDTs, which detect antigens derived from the parasites, most often use a cassette or dipstick and provide results in two to 10 minutes. These tests are being used in some countries, but they are not approved by the Food & Drug Administration for use in the United States. A molecular diagnosis technique, which detects parasitic genetic material, is more accurate than microscopy, but it is expensive and requires a specialized laboratory.

In areas where malaria is common, such as certain African countries, rural healthcare facilities lack microscopes and trained personnel. In these cases, workers presume that a person with a fever that does not have an obvious cause has malaria and will treat the patient for the disease.

Treatment and Prevention of Malaria
Malaria is curable if the right drugs are used for the correct period of time. Because some types of the parasites in some regions have developed resistance to the most commonly used antimalarial drug, an accurate diagnosis is essential to selecting the appropriate treatment. If you are in an area where malaria is common and you develop flu-like symptoms, immediately get tested. Timely treatment can prevent the infection from causing more harm and from spreading to other people. You can learn more about the specific drugs used to treat malaria in How Malaria Drugs Work.

bed net
Photo courtesy Amazon.com
Using a bed mosquito net in areas where malaria is common is one way to prevent exposure.

When traveling to areas where malaria is common, you should avoid exposure when possible, use insecticide-treated bed nets, and wear protective clothing and insect repellant. Before you travel to tropical countries, visit the CDC's Traveler's Health: Regional Malarial Information site to learn what specific prescription drugs will offer you protection from this serious disease. The CDC also provides specific guidance on protecting yourself from mosquitoes at its Traveler's Health: Mosquito and Tick Protection site.

For lots more information on malaria, mosquitos and related topics, check out the links on the following page.

­

Related HowStuffWorks Articles

More Great Links

Sources

  • "Diagnosis." CDC.
    http://www.cdc.gov/malaria/diagnosis_treatment/diagnosis.htm
  • "Frequently Asked Questions About Malaria." CDC.
    http://www.cdc.gov/malaria/faq.htm
  • "Frequently-Asked-Questions about Malaria." Roll Back Malaria.
    http://www.rollbackmalaria.org/
  • "Malaria." Global Health Reporting.
    http://www.globalhealthreporting.org/malaria.asp
  • "Malaria." The Special Programme for Research and Training in Tropical Diseases (TDR).
    http://www.who.int/tdr/index.html
  • "Malaria." World Health Organization.
    http://www.who.int/topics/malaria/en/
  • "Part 2: Treatment: General Approach & Treatment: Uncomplicated Malaria." CDC.
    http://www.cdc.gov/malaria/diagnosis_treatment/clinicians2.htm
  • "Regional Malarial Information". CDC.
    http://www.cdc.gov/travel/regionalmalaria/cafrica.htm#antimalarialdrugs