Malaria, in second place, sees fewer victims, but greater difficulty of control.

Malaria is the world's most deadly tropical parasitic disease which kills more people than any other communicable disease, except tuberculosis. Although the geographical area affected by malaria has shrunk considerably over the past 50 years, control is becoming more difficult, and gains have been eroded. The disease is transmitted by Anopheline mosquitoes, the number and type of which determine the extent of transmission in a given area. Increased risk of the disease is linked with changes in land use related to activities like road building, mining, logging and agricultural and irrigation projects, particularly in frontier areas like the Amazon, and in South-East Asia. Other causes of its spread include global climatic change, disintegration of health services, armed conflicts and mass movements of refugees. The emergence of multi-drug resistant swains of parasite is also exacerbating the situation. As a result of the explosion of international travel, imported cases of malaria are now more frequently registered in developed countries. Malaria is re-emerging in areas where it was previously under control or eradicated, e.g. in the Central Asian Republics of Tajikistan and Azerbaijan, and in Korea.

Malaria endemic countries are some of the poorest in the world and results in costs to the affected countries in terms of the control of the disease and lost workdays - estimated to be I to 5 per cent of the gross domestic product in Africa. For the individual, costs include the price of treatment and prevention, and lost income. In rural areas, the rainy season is often a time of intense agricultural activity when poor families earn most of their annual income. Malaria can make these families poorer. The disease can lead to chronic absenteeism and impairment of learning ability in affected children. Urban malaria is increasing due to unplanned development around large cities, particularly in Africa and South Asia.

According to WHO, "global warming" and other climatic events such as "El Nino" also play a role in increasing the risk of the disease. Malaria has now spread to highland are of Africa, while El Nino events have an impact on malaria because the associated weather disturbances influence vector-breeding sites, and hence the transmission of the disease. Quantitative leaps in malaria incidence, coincident with ENSO (El Nino/Southern Oscillation) events, have been recorded around the world - in Bolivia, Colombia, Ecuador, Peru, Venezuela, Rwanda, Pakistan and Sri Lanka.

In addition, the phenomenon of "airport malaria" or the importing of malaria by international travellers is becoming commonplace. Even "weekend malaria", which happens when city dwellers in Africa return to their rural settings, is becoming an increasing problem.

Prevention of the disease encompasses a variety of measures that may protect against infection - directed against the mosquito vector - or against the development of disease in infected individuals. In spite of drug resistance, WHO stresses that malaria is a curable disease, not an inevitable burden. Although there is only a limited number of drugs, if these are used properly and targeted to those at greatest risk, malaria disease and deaths can be reduced. In the last decade, considerable progress has been made in the search for a malaria vaccine. More than a dozen candidate vaccines are currently in development, some of them in clinical trial. An effective vaccine could be available within the next 7 to 15 years.

Every Half Minute, a Child Dies

According to WHO statistics, malaria kills one child every 30 seconds. In absolute numbers, malaria kills 3,000 children per day under five years of age. It is a death toll that far exceeds the mortality rate from acquired immune deficiency syndrome (AIDS). African children under five years are chronic victims of malaria, suffering an average of six bouts a year. Fatally-afflicted children often die less than 72 hours after developing symptoms. And yet, says WHO, protection of children can be easy. Randomized control trials conducted in the Gambia, Ghana, Kenya and Burkino Faso, for example, show that about 30 per cent of child deaths could be avoided if they slept under bednets regularly treated with insecticides such as pyrethroids, which remains effective for 6 to 12 months.

Malaria is particularly dangerous during pregnancy. If causes severe anaemia and is a major factor contributing to maternal deaths in malaria endemic regions. Pregnant mothers, who have malaria and are HIV-positive, are more likely to pass on their HIV status to the unborn child. The United Nations Children's Fund has made tackling the disease a top priority, because it is one of the major contributors to under-five mortality, and supports malaria control programmes in 32 countries, 27 of which are in Africa.

Point of Fact: Malaria is endemic in Africa (45 countries), the Americas (21), Europe (4), Eastern Mediterranean (14), South-East Asia (8) and the Western Pacific (9).