Prevalence

The geographical area affected by malaria has shrunk considerably over the past 50 years, but control is becoming more difficult and gains are being eroded. Increased risk of the disease is linked with changes in land use linked 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 strains of parasite is also exacerbating the situation. Via the explosion of easy 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.

There are some significant points regarding prevalence of the disease:

• Malaria is a public health problem today in more than 90 countries, inhabited by a total of some 2400 million people - 40% of the world's population.
• Worldwide prevalence of the disease is estimated to be in the order of 300-500 million clinical cases each year.
• More than 90% of all malaria cases are in sub-Saharan Africa.
• Mortality due to malaria is estimated to be over 1 million deaths each year.
• The vast majority of deaths occur among young children in Africa, especially in remote rural areas with poor access to health services.
• Other high-risk groups are women during pregnancy, and non-immune travellers, refugees, displaced persons and labourers entering endemic areas.
• Malaria epidemics related to political upheavals, economic difficulties and environmental problems also contribute in the most dramatic way to death tolls and human suffering.

Most affected are the tropical regions. It is in these areas that Plasmodium falciparum is rampant, capable of inducing pernicious malaria that can be fatal.

In Africa, malaria is widely distributed throughout the tropical regions, where a large number of areas are resistant to chloroquine, used to prevent Plasmodium falciparum. North Africa is very little affected and only by the much less dangerous Plasmodium vivax and Plasmodium malariae.
Reunion Island contains no risk of transmission. In Central and South America, important centres of chloroquine-resistant Plasmodium falciparum have developed. North America remains unaffected, as do Guadeloupe and Martinique. In Asia, Thailand, Vietnam, Cambodia and China in particular harbour the infection, with a large number of centres of resistance to chloroquine; it was here in these regions that the first resistant strains appeared.