Six-year old Marco Togbe, suffering from cerebral malaria, lies in hospital in Lome, Togo. Picture taken December 12, 2004. REUTERS/IFRC/Marko Kok

Malaria kills about 880,000 people every year, with children and pregnant women the most vulnerable. Recent figures suggest that, as of the end of 2004, 3.2 billion people in 107 countries and territories were at risk of malaria.

The World Health Organisation estimates that there are as many as 247 million cases of malaria annually, and 880,000 people die of the disease every year. However, analysts believe that the real figures are far higher, arguing than many cases occur in rural areas and are not recorded.

Sub-Saharan Africa accounts for more than 60 per cent of infections and 80 per cent of the deaths from the disease. Other countries affected by malaria are Brazil, Thailand, Vietnam, Cambodia, China, Sri Lanka, Indonesia and Afghanistan.

A fifth of all hospital cases worldwide are believed to involve the disease, and as many as a quarter of all child deaths are connected to malaria every year. Pregnant women are particularly vulnerable and their babies are also at risk of miscarriage or low birth rate.

As well as the staggering cost in terms of human life, malaria has a devastating effect on the economy. The developing world is hardest hit, with a single bout of malaria in Africa leading to a loss of around ten working days. For other countries, malaria can lead to loss of tourist revenue and international investment.

Infection occurs when a malarial mosquito, usually of the Anopheles genus, bites a human to drink blood, and parasites enter the bloodstream.

Only around 60 of the 400 species of Anopheles mosquito are though to spread the disease in this way, 30 of them on a large scale. Only the females drink blood, in order to boost the reproduction process.

Once transmitted, the parasites infect the liver and the red blood cells. The symptoms include bouts of fever (caused when the parasites burst out of the red blood cells)and shivering, aching bones and headaches.

Most people survive a bout of malaria after suffering from the disease for as long as 20 days, but only if the symptoms are spotted and treated early. More serious complications can occur when infected red blood cells clump together as this can cause damage to blood vessels and internal organs, including brain damage.

In regions where malaria is rife, the population gradually develops immunity to the disease after years of infection and reinfection. However, children are very vulnerable, as are pregnant women and those who are HIV positive.

In addition, some people are particularly susceptible to malaria because of genetic reasons such as the presence of sickle cell anaemia. However, treated properly and swiftly, the disease is curable.

Malaria has always been a killer, but its true nature was not understood until the 19th century. Hundreds of years ago, people though that the disease was caused by marsh gas and named mal air ia, which literally means bad air from swamps.

The first treatment for malaria, quinine, was being used long before scientists understood what caused the infection and how it spread. Evidence of quinine use dating back to the 14th century has been found in Peru, although scientists did not isolate the active ingredient until 1820.

However, the parasite can develop a resistance to quinine derivatives, particularly chloroquine, the most affordable and widely available drug on the market. As a result, a new treatment called artemisinin combination therapy, or ACT, has been introduced and is slowly replacing the obsolete antimalarials.

Given malaria's ability to adapt to the drugs used to treat it, many believe that prevention is key to reducing the impact of the disease. The World Health Organisation (WHO) is at the forefront of international efforts to contain and reduce the spread of malaria. Its work with the Roll Back Malaria global partnership, launched in 1998 by the WHO with UNICEF, UNDP and the World Bank, aims to halve the burden of malaria by 2010.

No effective vaccine has been developed to date, although several are being developed and tested, so experts are concentrating on other methods of prevention. These include the use of insecticides on known breeding grounds, and the provision and use of mosquito nets to shield sleeping humans from the insect. Netting incorporating insecticide is also a useful weapon against the disease. However, the most vulnerable communities are often the ones least likely to be able to afford such methods.

Malaria outbreaks have a devastating effect on poor rural communities, killing and debilitating the population, and having a serious knock-on effect on the economy.

Nomadic peoples, migrant workers and farmers are often most at risk, having moved from relatively safe areas into endemic ones in search of work and grazing. As they have not built up sufficient immunity, they soon fall victim to the disease.

Further problems arise when such infections occur in rural areas with poor healthcare provision. In such situations, inadequate or incomplete administration of antimalarial drugs can do little to help the victim, and indeed only increases the parasite's resistance to the drug treatments.

Experts believe that more people are now dying of malaria that did so three decades ago, and warn that it is spreading to new countries.

The disease is now present in non-tropical countries such as Turkey and Russia. In addition, a handful of people die of malaria every year in the United States, a country that eradicated the disease back in the 1950s.

Although it is mainly a disease of tropical and sub-tropical countries, malaria has been identified in eastern European countries such as Russia and Turkey and recently a handful of cases were diagnosed in the US.

Many factors have been blamed for this, including increased resistance to antimalarial drugs; political and social upheaval which moves populations into endemic areas; changes to the environment such as road building and irrigation, providing ideal breeding habitats for mosquitoes; budget restraints in developing countries, and the mosquitoes' growing resistance to modern insecticides.