Malaria
A Guide for Travelers

Excerpted from CDCP, where you can find much more information.
Malaria's distribution by geographical area | An excellent page on malaria

Causes

Malaria is caused by a parasite that is transmitted from person to person by the bite of an infected "Anopheles" mosquito. These mosquitoes are present in almost all countries in the tropics and subtropics. "Anopheles" mosquitoes bite during nighttime hours, from dusk to dawn. Each of the four different strains of malaria has different symptoms and reacts differently to antimalarial drugs. The "Falciparum" parasite is the deadliest of the four malaria parasites, but it is rarely encountered. The "Vivax" parasite is the most common cause of malaria.
Malaria kills three million people worldwide every year.

Symptoms:

Symptoms include fever, chills, headache, muscle ache, and malaise. Early stages of malaria may resemble the onset of the flu. Malaria symptoms can develop as early as 6-8 days after being bitten by an infected mosquito or as late as several months after departure from a malarious area, after antimalarial drugs are discontinued.

Prevention:

There is no vaccine for malaria. The risk of malaria can lowered by the use of antimalarial pills. Chloroquinine is no longer effective, and Fansidar has dangerous side effects. Mefloquine ("lariam") is the most widely used anti-malaria drug. The pills are generally started a week or two before arrival in the risk area. Malaria pills must be taken regularly (daily or weekly depending on the drug) while you are at risk, and for four to six weeks after you leave a malarious area. If you stop taking pills too soon, you will increase the chances of getting full-blown malaria.
A newcomer is Malarone, which can be taken just 24 hours before starting the trip.

Precautions

Avoiding mosquito bites is the only way to be sure of not getting malaria: spray your face and hands with insect repellent, wear long-sleeve shirts and long pants, use a mosquito net at night.

Contagiousness

Malaria is not contagious

Duration

Malaria may last for life.

Treatment

Malaria can be treated effectively in its early stages, but delaying treatment can have serious consequences.