What causes Malaria?
A tiny singled-celled creature called Plasmodium. In order to complete its life-cycle, Plasmodium must live both in an insect host - specifically the female Anopheles mosquito - and a human host. If an Plasmodium infected mosquito bites a human, the parasite passes into the person's bloodstream and heads straight for the liver. There it invades the liver-cells and multiplies. Two weeks later, the Plasmodium bursts out of the liver and spills into the blood-stream where it begins a repeated cycle of invading red blood cells, multiplying still more and then bursting out of the cells and re-invading more red blood cells. At this point the infected person experiences symptoms of malaria such as fever, vomiting and headaches followed by chills. If left untreated, they may develop anaemia - and in some cases, the patient goes into a coma and will probably die. This is known as Cerebral Malaria.
Types of Malaria parasite in Humans
There are 4 different species of Plasmodium which cause malaria in humans but the 2 most important are Plasmodium falciparum - which is the most severe form - and Plasmodium vivax. Plasmodium falciparum is the predominant form of the malaria parasite in Africa whereas Plasmodium vivax is much more common in Asia and South America. The other two forms of the parasite are called Plasmodium ovale and Plasmodium malaria.
This species was originally sensitive to chloroquine, however, strains resistant to this and other antimalarial drugs are now commonplace. Because the parasite is able to multiply very rapidly and sequester within the microvasculature, a life threatening illness may develop in a very short space of time.
Most strains of P. vivax are still sensitive to chloroquine although some chloroquine resistant strains have been reported in Papua New Guinea, Indonesia, Thailand and India. This drug will clear the erythrocyte stages of the parasite but it has no effect on the exo-erythrocytic liver stage and a course of primaquine (an 8-amino-quinoline) is required for radical cure. The Chesson strain of P. vivax found in New Guinea shows some resistance to primaquine and an increased dose of primaquine is required. If primaquine is not given, the patient may suffer a relapse which will occur weeks or months after the original attack.
P. malariae, P. ovale.
Treatment for the eradication of these two strains of malaria is the same as that for P. vivax except it is not necessary to give primaquine to those patients with P. malariae
Artemisinin has been used for many years by the Chinese as a traditional treatment for fever and malaria. It is a sesquiterpene lactone derived from Artemisia annua. Because it is being increasingly used in a number of countries and is both cheap and effective it was decided to include treatment schedules here. However, it is not yet licensed for use in Australia, North America or Europe. Its main value at present is in the treatment of multi drug resistant falciparum malaria. If artemisinin is used to treat vivax malaria it should be accompanied by a course of primaquine. Unless used with a second antimalarial as described below there is likely to be a high recrudescent rate. Side effects have been reported but these are comparatively rare and seldom severe. It is recommended only for treatment not for prophylaxis.