At the very edge of a fresh epoch in time, new micro-organisms capable of causing disease in human beings continue to be detected. Will each emerging micro-organism develop into a public threat? It depends. Primarily on factors related to the micro-organism and its environment. And also on the infected person and surrounding environment.

Such factors include ease of transmission between animals and people. And among people. The potential for spread beyond the immediate outbreak site. The severity of the illness. The availability of effective tools to prevent and control the outbreak. And the ability to treat, if not vanquish, the disease. But, be warned. Some of the new agents detected over the past 25 years are now genuine public health problems. On a local, on a regional, on a global scale.

Emerging infectious diseases result from newly identified and previously unknown infections, which cause public health problems either locally or internationally. A recent example of an emerging disease is the new variant of Creutzfeldt-Jakob disease, which was first described in the United Kingdom in 1996. The agent is considered to be the same as that causing bovine spongiform encephalitis, a disease which emerged in the 1980s and affected thousands of cattle in the United Kingdom and some other European countries.

Examples of emerging diseases associated with viruses:

• Ebola virus: The first outbreaks occurred in 1976 and the discovery of the virus was reported in 1977. Indigenous cases have been confirmed in four countries in Africa - Côte d'Ivoire, Democratic Republic of the Congo, Gabon and the Sudan. Through June 1997, 1,054 cases had been reported to the World Health Organization (WHO), 754 of which proved fatal. Monkeys infected with an Asian strain of Ebola were imported from the Philippines into the United States in 1989 and 1990, and into Italy in 1992. This Asian strain, Ebola-Reston, does not appear to cause illness in humans.
  
  
• Human immunodeficiency virus (HIV) which causes acquired immune deficiency syndrome (AIDS) was first isolated in 1983. It is estimated that since the start of the epidemic 30.6 million people worldwide have become HIV infected and nearly 12 million have died from AIDS or AIDS-related diseases.
  
  
• Hepatitis C, identified in 1989, is now known to be the most common cause of post-transfusion hepatitis worldwide, with approximately 90 per cent of cases in Japan, the United States and Western Europe. Up to 3 per cent of the world population are estimated to be infected; 170 million are chronic carriers at risk of developing liver cirrhosis and/or liver cancer.
  
  
• Sin nombre (i.e., an unnamed) virus was isolated from cases of a local outbreak of a highly fatal respiratory disease in the southern United States in 1993. It has subsequently been diagnosed in sporadic cases across the United States, Canada and several South American countries.
  
  
• Influenza A(H5N1) virus is a well-known pathogen in birds, but was first isolated from humans in 1997. Its emergence initially suggested the next influenza pandemic but, in the event, the virus transmitted poorly and the spread of the virus appeared to have been contained in 1997.

• Legionella pneumophilia: The detection of the bacterium in 1977 explained an outbreak of severe pneumonia in a convention centre in the United States in 1976 and it has since been associated with outbreaks linked to poorly maintained air conditioning systems.
  
  
• Escherichia coli O157:H7: Detected in 1982, this bacterium is typically transmitted through contaminated food and has caused outbreaks of haemolytic uraemic syndrome in North America, Europe and Japan. A widespread outbreak in Japan in 1996 caused over 6,000 cases among school children, among whom 2 died. During a single outbreak in Scotland in 1996, 496 people fell ill, of whom 16 died.
  
  
• Borrelia burgdorferi: Detected in the United States in 1982 and identified as the cause of Lyme disease, this bacterium is known to be endemic in North America and Europe and is transmitted to humans by ticks.
  
  
• Vibrio cholerae O139: First detected in 1992 in India, this bacterium has since been reported in seven countries in Asia. The emergence of a new serotype permits the organism to continue to spread and cause disease even in populations protected by antibodies generated in response to previous exposure to other serotypes of the same organism.
  

Please use this version of the article for printing.

Next Page of this article

EXAMPLES OF PATHOGENS RECOGNIZED SINCE 1973: Rotavirus: Major cause of infantile diarrhoea globally (1973) Cryptosporidium parvum: Acute and chronic diarrhoea (1976) Ebola virus: Ebola haemorrhagic fever (1977) Legionella pneumophilia: Legionnaires disease (1977) Hantaan virus: Haemorrhagic fever with renal syndrome (1977) Campylobacter jejuni: Enteric diseases distributed globally (1977) Human T-lymphotropic virus 1 (HTLV-1): T-cell lymphoma-leukemia (1980) Toxin-producing strains of Staphylococcus aureus: Toxic shock syndrome (1981) Escherichia coli O157:H7: Haemorrhagic colitis; haemolytic uraemic syndrome (1982) HTLV-II: Hairy cell leukemia (1982) Borrelia burgdorferi: Lyme disease (1982) HIV: AIDS (1983) Helicobacter pylori: Peptic ulcer disease (1983) Hepatitis E: Enterically transmitted non-A, non-B hepatitis (1988) Guanarito virus: Venezuelan haemorrhagic fever (1990) Encephalitozzon hellem: Conjunctivitis, disseminated disease (1991) Vibrio cholerae O139: New strain associated with epidemic cholera (1992) Bartonella henselae: Cat-scratch disease; bacillary angiomatosis (1992) Sabia virus: Brazilian haemorrhagic fever (1994) Hepatitis G virus: Parenterally transmitted non-A, non-B hepatitis (1995) Human herpesvirus-8: Associated with Kaposi sarcoma in AIDS patients (1995) TSE causing agent: New Variant Creutzfeldt-Jakob disease (1996) Avian Influenza [Type A (H5N1)]: Influenza (1997)