Malaria

Malaria is a mosquito borne parasitical disease. Certain species of mosquitos take in the parasite from infected persons when they bite them and pass them on to the next person they draw blood from. Malaria kills more people every year than any other living organism, and there are over 200 million active cases at any given time, leading to over 700,000 deaths every year.
Once inside the body, the parasite attacks red blood cells, feeding off of them and using them to reproduce. As a result anemia is common with malaria patients. The parasites coordinate their attacks so that most of the time, they may only be found within the red blood cells where they cannot be found by the immune system and the drugs used to treat the condition are similarly ineffective. However, every 48 hours, all the parasites are released simultaneously into the blood, usually resulting in an intermittent fever. As a result, there are usually not enough antibodies built up in order to destroy all the parasites.
Malaria has been known as a distinct disease since ancient times. Europeans first became exposed to it when they colonized areas of Africa and Asia where it is endemic. However, the cause of the disease was not well understood until the 19th century. Prior to that, it was thought the disease was the result of exposure to marsh gases from swampy areas (hence the name of the disease is literally the Italian for "bad air"). However, as we now know, the role of swamps in transmitting the disease is that they provide breeding grounds for the mosquitos that carry the disease.
It was discovered in the mid 19th century that Quinine, an extract of cinchona tree is effective in both treating and preventing the disease. However, the cinchona only grows naturally in South America, which for decades had a monopoly on the production of the drug. However, in modern times Chloroquine is the treatment of choice for most patients. However, malaria has another trick - it is immune from these drugs when the parasite spends part of its life cyle in the liver. In this stage, the disease usually presents with jaundice. As a result, one exposed, patient's must be monitored regularly thereafter as relapses are common even if the disease has been inactive for years.
Although it is virtually unknown in the western world, Malaria is still endemic in tropical regions and results in millions of deaths each year. However, many travellers to the tropics also contract the disease every year. Since the disease is not contagious, patients can be treated in general hospitals without special precautions.
Prevention of the spread of mosquitos is also effective in treating the disease. Draining swamps and other sources of stagnant water denies the mosquito a place to breed. Many cities in the tropics, such as Nairobi, are deliberately sited at high altitude which makes it too cold for mosquitos to survive and breed.
Malaria at Wikipedia
Malaria at the Mayo Clinic
Malaria