Malaria is caused by protozoan parasites of the genus Plasmodium. Four species of Plasmodium can produce the disease in its various forms - Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale & Plasmodium malaria. P. falciparum is the most widespread & dangerous of the four: untreated it can lead to fatal cerebral malaria.
Parasites are transmitted from one person to another by the female anopheline mosquito.
The parasites develop in the gut of the mosquito & are passed on in the saliva of an infective mosquito each time it takes a new blood meal. The parasites are then carried by the blood in the victim's liver where they invade the cells & multiply.
After 9-16 days they return to the blood & penetrate the red cells, where they multiply again, progressively breaking down the red cells. This induces bouts of fever & anaemia in the infected individual. In cerebral malaria, the infected red cells obstruct the blood vessels in the brain. Other vital organs can also be damaged often leading to the death of the patient.
Malaria is diagnosed by the clinical symptoms & microscopic examination of the blood. It can normally be cured by antimalarial drugs. The symptoms quickly disappear once the parasite is killed. In certain regions, however, the parasites have developed resistance to certain antimalarial drugs, particularly chloroquine. Patients in these areas require treatment with other more expensive drugs. Cases of severe disease including cerebral malaria require hospital care.
In endemic regions, where transmission is high, people are continuously infected so that they gradually develop immunity to the disease. Until they have acquired such immunity, children remain highly vulnerable. Pregnant women are also highly susceptible since the natural defence mechanisms are reduced during pregnancy.
Malaria remains the world's No. 1 infectious disease, & the risk to those traveling to countries in the tropics & subtropics is increasing. Even if your exposure will be brief, such as one night's travel to a malarious area, you should take protective measures. It is possible to contract malaria during brief stopovers at airports in malarious zones if officials have not taken proper measures to rid the area of mosquitoes (airports off the main international circuit are particularly suspect).
Malaria occurs in many parts of the world, including Central & South America, Africa, India, Southeast Asia, the Middle East, & islands of the South Pacific. Risk is highest between dusk & dawn because the mosquitoes feed at night. Malaria is occasionally acquired by drug addicts who use contaminated syringes, through blood transfusion from an infected person, or by congenital transfer from mother to fetus.
The disease is characterized by fever & "flu-like" symptoms that may come & go, including chills, headache, muscle ache, and/or a vague feeling of illness. Vomiting or diarrhea may also occur. There may be anemia & jaundice (yellowing of the skin & whites of the eyes). Malaria symptoms can develop as early as 7 days after first being exposed & as late as several months or even longer after leaving a malarious area, when use of preventive drugs has been stopped (see Preventive Therapy). If treatment is not received for falciparum malaria, it can proceed to shock, liver & kidney failure, coma & death. While illness caused by vivax, ovale or malariae is not usually life-threatening, it can pose serious risks to the very young or very old, or to those with other illnesses. If these types of malaria are left untreated, episodes may recur at irregular times for months or possibly years, & the malariae form can recur more than 25 years after exposure.
Malaria should be suspected if you have any of the symptoms noted above, even if they are mild, & medical help should be sought immediately.