Published by Australian Academy of Science
KEY TEXT Malaria – a growing threat This topic is sponsored by The Walter and Eliza Hall Institute of Medical Research.

You will get more from this topic if you have mastered the basics of the immune system – these links will take you to an annotated list of sites with helpful background information.

Malaria is one of the leading causes of illness and death in the world. According to the World Health Organization, between 300 to 500 million people contract malaria every year and up to 2.7 million die from it. Nine out of ten of these deaths occur in Africa. The rest occur in Asia and Latin America. People suffering from malaria are often anaemic and have enlarged spleens. They are also susceptible to other infections.

Mosquitoes spread the disease

Malaria is caused by a parasite (Plasmodium) that lives in red blood cells and cells of the liver. The parasite is transmitted from person to person by the female Anopheles mosquito (Box 1: Life cycle of malarial parasite).

What has been done to control malaria?

During the 1950s the World Health Organization carried out a program to eradicate malaria from some parts of the world. Insecticides, mainly DDT, were used to control mosquito populations. At first this program was successful, and malaria was eradicated from southern Europe, the United States and the former Soviet Union. But it soon became clear that, in hotter and more humid climates where mosquitoes are present all year long, they had become resistant to the insecticides being used.

Related site: Malaria: Past and present Describes the history of malaria research and early attempts to control the disease. (Nobelprize.org, Sweden)

Other methods to control malaria were attempted, including drug treatment of whole populations, but the malarial parasites became resistant to the drugs. By 1970, with the number of cases of malaria increasing, it became obvious that the program had failed.

Fighting malaria on two fronts

Today, the battle against malaria is continuing on two fronts: fighting mosquitoes and fighting the disease itself (Box 2: Controlling malaria).

• Fighting mosquitoes. A range of methods are used to deal with mosquitoes. A simple but effective method is for people to sleep under nets that have been soaked in insecticide. This is being tried in Vietnam and parts of Africa and has been found to reduce the incidence of the disease.

• Fighting the disease. Good health care, with early detection and full treatment with drugs, is essential. Unfortunately, most cases of malaria occur in countries that cannot afford such programs.

Drugs can treat malaria

Malaria can be treated successfully with a variety of drugs if it is caught early enough. Until recent years, quinine was the most effective drug given for cases of cerebral malaria. But some forms of the malarial parasite have become resistant to quinine. New and more expensive drugs have to be administered in these cases.

Fortunately, two recent studies have shown that an old Chinese herbal remedy made from the shrub, Artemisia annua, can effectively treat quinine-resistant malaria. The active compound – artemisinin – derived from this plant has been shown to clear the parasite from the blood more quickly and with fewer side effects than quinine-based drugs. This is good news for Africa, where the majority of malaria cases occur. The recent discovery of exactly how artemisinin kills the malarial parasite may lead to a series of new anti-malarial drugs.

Progress towards a malaria vaccine

Related site: Malaria vaccines Describes a number of campaigns aimed at controlling malaria and Australian research on malaria vaccines. (Medical Journal of Australia)

Vaccines work by getting the body's immune system to respond to particular antigens produced by the disease-causing organism – in this case, the malarial parasite. Unfortunately, the malarial parasite is constantly changing, so its antigens are also constantly changing. But progress is being made, with researchers around the world racing to produce an effective anti-malaria vaccine (Box 3: Anti-malaria vaccine).

Malaria in Australia

The last major outbreak of malaria in Australia occurred at the end of World War II, when servicemen infected with malaria returned from Papua New Guinea. But it was not until 1981 that Australia was officially declared malaria-free by the World Health Organization. Even so, there are about a thousand reported cases of malaria in Australia each year, and one death a year. However, the vast majority of these people contracted the disease overseas.

Fortunately, the isolation of communities in northern Australia and the small population ensure that there is no human reservoir of the disease. If a person does contract malaria, the health services are quickly informed, the infected person is treated and the community is tested for malaria.

Boxes

1. Life cycle of malarial parasite

2. Controlling malaria

3. Anti-malaria vaccine

CREDITS

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