Encyclopedia / M / Malaria



Malaria is an infectious disease caused by a parasite (plasmodium) which is transmitted from human to human by the bite of infected female Anopheles mosquitoes.


Four species of the parasite plasmodium are responsible for malaria in humans: Plasmodium vivax, Plasmodium malariae, Plasmodium ovale, and Plasmodium falciparum.

Malaria continues to be endemic in many parts of the tropics and subtropics. Today, the number of cases is rising worldwide. Malarial parasites cause clinical illness in an estimated 300 to 500 million people every year and cause 1.5 to 2.7 million deaths per year.

Each year in the U.S., there are an average of 1000 imported infections; a few cases of locally acquired, mosquito-transmitted infection from an imported case; and an average of four deaths from falciparum malaria. Most of the imported infections are acquired from tropical Africa.

The female Anopheles mosquito becomes infected by ingesting blood containing the sexual forms of the parasite plasmodium. After developing in the mosquito, the plasmodium is inoculated into humans when the mosquito next feeds (bites).

The first stage of plasmodium development in humans takes place in the liver. When the more mature plasmodium escape from the liver and enter the bloodstream, they infect red blood cells and multiply, causing the red blood cells to burst open after about 2 to 3 days and to release a new crop of parasites (plasmodium). The cycle of invasion, multiplication, and red blood cell rupture may be repeated many times.


Malaria comes from being bitten by a mosquito carrying the malaria organism. Risk factors include traveling in areas in which such mosquitoes are found or, rarely, being bitten by a mosquito that has previously fed on an "imported" case of malaria (such that the case can occur in an area of the world where malaria is not endemic).


Malarial attacks present over 4 to 6 hours with shaking chills, high fever, and sweating, and are often associated with fatigue, headache, dizziness, nausea, vomiting, abdominal cramps, dry cough, muscle or joint pain, and back ache. The attacks may occur every other day or every third day.

Cerebral malaria and death can occur, sometimes within 24 hours, if the infection is caused by plasmodium falciparum.

Fever or other symptoms can develop in malaria as early as 8 days or as late as 60 days after exposure or stopping prophylaxis. For plasmodium vivax in temperate areas, the delay may be up to one year.


Methods of diagnosis are:

  • complete medical history of symptoms and travel
  • physical examination
  • blood tests, including thick and thin blood films, to identify the plasmodium species responsible for infection


**Medical treatment should be sought immediately.**The effectiveness of antimalarial drugs differs with different species of the parasite and with different stages of the parasite's life cycle. Your physician will determine the treatment plan most appropriate for your individual condition.

Drugs include chloroquine, mefloquine, primaquine, quinine, pyrimethamine-sulfadoxine (Fansidar), and doxycycline. Some plasmodium have developed resistance to certain medications, and therefore, alternative medications will be prescribed for you.


Are preventive measures necessary for the region of the world I'll be visiting?

Is this a high-risk area for malaria?

What drugs can be taken as a preventive measure?

What is the correct dosage?

When should the drug be started and stopped?

What other precautions should I take; repellents, clothes, nets?

What symptoms should I look for?

No prophylactic regimen gives complete protection. Speak with your physician or local travel clinic to receive up to date information about the best malaria protection for you. Effectiveness of any given medication varies by the region of the world in which you plan to travel. Effectiveness also varies from year to year, so current information is essential.

Prevention is based on:

  • evaluating the risk of exposure to infection
  • preventing mosquito bites by using DEET mosquito repellant, bed nets, and clothing that covers most of the body
  • chemoprophylaxis (preventive medications)