Malaria occurs due to one of several parasites called sporozoites, and it is transmitted to humans by insect bites. There are an estimated 300-500 million cases of malaria annually, with more than a million fatalities. Most of these cases occur in the tropics and subtropics, causing a hazard to both natives of these areas and to travelers who visit them.
Upon infection, the sporozoites travel through the blood to the liver, where they mature into another form of the parasite called merozoites. These merozoites then reenter the bloodstream and attack the host's red blood cells, multiplying quickly and then bursting open the infected red blood cells to release the newly formed merozoites into the bloodstream again. This enables them to spread extremely quickly throughout the body. Symptoms of malaria include fever and chills, headache, nausea, bloody stools, anemia, vomiting, and muscle pain. In more severe situations, the victim may lapse into a coma or undergo convulsions.
People who contract malaria should head to the nearest hospital for treatment. Practitioners may try to treat the infection with chloroquine, but many areas of the world include strains of chloroquine-resistant malaria. In these cases, other treatments may be used. Intravenous fluids and oxygen may be required to treat the symptoms of the disease. When malaria is treated, the prognosis is good. Complications of malaria - however, such as cerebritis (brain infection), hemolytic anemia (blood cell destruction), kidney or liver failure, meningitis, or respiratory failure - can decrease the likelihood of survival.
People who visit a country where malaria is common should take preventative medications before traveling. Natives of these countries often have some level of innate immunity. Both these natives, as well as travelers who have actually taken preventative medications, can still become infected. They should take precautions against mosquito bites by applying insect repellant and covering up as much skin as possible.