Distribution and Incidence

Although the eradication campaigns of the 1950s and 1960s contributed to substantial declines in the incidence of malaria in many countries, and to the elimination of transmission in some, malaria persists as a major contributor to ill health in vast areas of the tropical and subtropical world. Reported cases of malaria are increasing from year to year, especially in areas of Asia and the Americas undergoing agricultural colonization with forest clearing and pioneering of unexploited lands. Eradication campaigns have given way to long-term control programs in most areas where the disease remains endemic, and in some countries control is now being linked to or integrated with systems of primary healthcare (Bruce-Chwatt 1987; Hilton 1987).

The present global situation has been categorized by David Clyde (1987) as follows:

1. Areas where malaria never existed or disappeared spontaneously (with a current population totaling some 1.3 billion)

2. Areas where control and eradication campaigns, in combination with other factors, have eliminated endemic malaria in recent years (population about 800 million)

3. Areas under continuing control, including most endemic countries of Asia and the Americas (population about 2.2 billion)

4. Areas with little or no organized control, mainly in Africa south of the Sahara (population about 400 million)

Table Vin.85.1. Malaria in 1984

No. of cases reported

to the World Health

Population at risk

Estimated incidence per

Geographic areas

Organization

(millions)

1,000 population at risk

The Americas

914,000

179

11.8

Europe, including Turkey and

60,000

47

2.1

former Soviet Union

Africa south of the Sahara

5,000,000°

385

202.6

North Africa and western Asia

305,000

166

5.4

Central and South Asia

2,711,000

844

10.5

Eastern Asia and Oceania

1,300,000

1,069

7.5

Total

10,290,000

"Estimated; mainly clinical diagnoses.

Source: Adapted from World Health Organization data and Clyde (1987, tables 1 and 2).

"Estimated; mainly clinical diagnoses.

Source: Adapted from World Health Organization data and Clyde (1987, tables 1 and 2).

Reported cases, and estimates for Africa south of the Sahara, are summarized in Table VIII.85.1 for 1984, together with incidence estimates. The total of some 10 million cases probably represents less than 10 percent of actual cases for that year because of reporting and surveillance deficiencies. Clyde (1987) believes that the infected population in 1984 may actually have exceeded 100 million in a population at risk of 2.6 billion. Malaria-related deaths are also poorly reported; David Hilton (1987) notes that worldwide estimates of deaths are still in the range of hundreds of thousands every year.

The Americas. The United States, Canada, and most countries of the Caribbean are essentially free of malaria transmission and report only small numbers of imported cases. Costa Rica, Panama, and several southern South American countries are also nearly free of local transmission. Haiti and the Dominican Republic report only P. falciparum cases, although in substantial numbers. P. vivax is the prevailing species in Mexico, Central America, and northern South America, although many P. falciparum cases are also reported, especially from Brazil, Colombia, and Ecuador. Europe, Turkey, and the former Soviet Union. Malaria is no longer endemic in Europe and the Soviet Union, but Turkey still reports some autochthonous cases. Africa south of the Sahara. About 90 percent of the population in this region is still at risk, and transmission is high in many areas, especially in rural West Africa (Spencer 1986). P. falciparum is the predominant species. North Africa and western Asia. Only a few small foci of autochthonous transmission persist in this region.

Central and South Asia. Malaria remains endemic in most countries of the region. P. vivax is predominant, but P. falciparum is also important, and this species appears to be increasing in relative prevalence (Spencer 1986). Eastern Asia and Oceania. The northeastern area of Asia, including Japan, is free of transmission, as are many of the smaller islands and island groups in Oceania. Endemic foci persist in some of the larger island areas (e.g., the Philippines, the Solomon Islands, Papua New Guinea, and Indonesia) and in most of mainland Southeast Asia and China. P. vivax prevails in China, where the incidence is steadily declining. In Thailand, which is also experiencing a decline in incidence, P. falciparum is somewhat more prevalent than P. vivax.

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