World health report

Executive summary


Emerging diseases

Emerging infectious diseases are those whose incidence in humans has increased during the last two decades or which threatens to increase in the near future. The term includes newly-appearing infectious diseases or those spreading to new geographical areas. It also refers to those that were easily controlled by chemotherapy and antibiotics but have developed antimicrobial resistance.

The most dramatic example of a new disease is AIDS, caused by the human immunodeficiency virus (HIV), whose existence was unknown until 15 years ago. About 26.6 million adults could be living with HIV/AIDS by the year 2000.

A new breed of deadly haemorrhagic fevers, of which Ebola is the most notorious, have struck in Africa, Asia, Latin America and the United States. Ebola appeared for the first time in Zaire and Sudan in 1976 and has emerged several times since, most notably in Zaire in 1995, where it was fatal in about 80% of cases.

The United States has seen the emergence of hantavirus pulmonary syndrome with a case fatality rate of over 50%. Other hantaviruses have been recognized for many years in Asia.

Epidemics of foodborne and waterborne infections due to new organisms such as cryptosporidium or new strains of bacteria such as E. coli O157:H7 have hit industrialized as well as developing countries. A completely new strain of cholera, O139, appeared in south-east India in 1992 and has since spread to other areas of India and parts of South-East Asia.

Despite the emergence of some 29 new diseases in the last 20 years, there is still a lack of national and international political will and resources to develop and support the systems necessary to detect them and stop their spread. Without doubt, diseases as yet unknown but with the potential to be the AIDS of tomorrow, lurk in the shadows.

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