UN Chronicle: Issue 1, 1999: Emerging and Re-Emerging Infectious Diseases

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.

Examples of emerging diseases associated with bacteria:

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.

Another emerging public health issue is the rapidly growing number of bacteria becoming resistant to an increasing range of antibiotics. In many regions, the low-cost, first-choice antibiotics have lost their power to clear infections of Escherichia coli, Neisseria gonorrhoea, Pneumococcus, Shigella, Staphylococcus aureus, increasing the cost and length of treatment of many common diseases, including epidemic diarrhoeal diseases, gonorrhoea, pneumonia and otitis. Further problems stem from the use of anti-microbial substances in food animal production.

Re-emerging infectious diseases are due to the reappearance and increase in the number of infections from a known disease which had formerly caused so few infections that it had no longer been considered a public health problem.

Cholera can emerge afresh where water and sanitation systems have deteriorated and food safety measures are not adequate. In 1991, the seventh cholera pandemic reached the Americas where cholera had not been registered for a century; over 390,000 cases were notified in over 10 South American countries, two thirds of the world total. In 1997, cholera outbreaks chiefly affected Eastern Africa. While overall numbers have declined since 1991, over 147,000 cases were reported globally in 1997. In 1998, the epidemic spread over eastern and southern Africa; new outbreaks occurred in South America.

Dengue fever has spread in many parts of South-East Asia since the 1950s and re-emerged in the Americas in the 1990s following deterioration in active mosquito control and spread of the vector into urban areas. Infection with dengue virus has often resulted in dengue haemorrhagic fever (DHF) in Asia but rarely in the Americas until a severe outbreak in Cuba in 1981. DHF has since spread, and during the epidemics in Central and South America in 1995-1997, DHF was reported in 24 countries.

Diphtheria re-emerged in the Russian Federation and some other republics of the former Soviet Union in 1994 and culminated in 1995 with over 50,000 cases reported. The re-emergence was linked to a dramatic decline in the immunization programmes following the disruption of health services during the unsettled times immediately after the break-up of the Soviet Union. Since then, immunization services have been re-established, reversing the upward trend: in 1996, 13,687 cases were reported in the Russian Federation.

Meningococcal meningitis occurs worldwide, but devastating, large-scale epidemics have mainly been in the dry Sub-Saharan regions of Africa, designated the "African meningitis belt". Since the mid-1990s, epidemics in this area have been on an unprecedented scale, and epidemic meningitis has also emerged in countries south of the Ameningitis belt". A new strain of Neisseria meningitidis (serogroup A clone III.1), which was first seen in the 1980s in Nepal and China, has spread west and has now been diagnosed in major meningitis outbreaks in Africa.

Rift Valley fever (RVF) is a zoonotic disease typically affecting sheep and cattle in Africa. Mosquitoes are the principal means by which RVF virus is transmitted among animals and to humans. Persons in contact with sick animals occasionally become infected. The disease in humans is typified by fever and myalgia but, in some cases, progresses to retinitis, encephalitis or haemorrhage. Following abnormally heavy rainfall in Kenya and Somalia in late 1997 and early 1998, RVF occurred over vast areas, producing disease in livestock and causing haemorrhagic fever and death among the human population. The extent of the outbreak and the severity of the disease was probably due to many factors, including climatic conditions, malnutrition and possibly route of infection.

Yellow fever (YF) is an example of a disease for which an effective vaccine exists but, because it is not widely used in many areas at risk, epidemics continue to occur. The threat of YF is present in 33 countries in Africa and 8 in South America. Since the mid-1980s, there has been a steady increase in the number of cases or of countries reporting cases (up to 5,300 per year worldwide); yet, the true number of cases occurring could be many times higher, as outbreaks in general occur in remote areas and miss the attention of health services. YF is typically a disease of the tropical forest areas where the virus survives in monkeys. Humans bring it back to their villages and, if a suitable mosquito vector is present, the disease will spread quickly and kill a large proportion of the population which has no immunity.

Why does it happen? Several factors contribute to the emergence and re-emergence of infectious diseases, but most can be linked with the increasing number of people living and moving in the world: rapid and intense international travel; overcrowding in cities with poor sanitation; substantially increased international trade in food, mass distribution of food and unhygienic food preparation practices; increased exposure of humans to disease vectors and reservoirs in nature; and alteration of the environment and climatic changes, which have a direct impact on the composition and size of the population of insect vectors and animal reservoirs. Other factors include a deteriorating public health infrastructure, which is unable to cope with the needs of the population.

Travel has always been a vehicle to spread disease across the world. According to data from the World Tourism Organization, over 550 million travellers were counted at national borders in 1995 and over 117 million of them had crossed continents to arrive at the destination. Luckily, the vast majority of infections brought along with travellers are common worldwide, and the disease is more a nuisance to the individual traveller than to society. The traveller can avoid many health risks with vaccines, protective measures against malaria and good personal hygiene.

For more details, see International Travel and Health, issued by WHO each year and accessible from WHO's website at http://www.who.ch/emc/.

Comments

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)

POINT OF FACT:

All but one of the diseases known to humankind still exist. Tuberculosis, once considered forgotten, has re-emerged as a global emergency.

WHO: RESOLUTION AND RESPONSE

In 1995, a resolution of the World Health Assembly urged all Member States to strengthen surveillance for infectious diseases in order to promptly detect re-emerging diseases and identify new infectious diseases. This resolution led to the World Health Organization's establishment of the Division of Emerging and other Communicable Diseases Surveillance and Control (EMC), whose mission is to strengthen national and international capacity in the surveillance and control of communicable diseases, including those that represent new, emerging and re-emerging public health problems.