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Emerging and Re-emerging Infectious Diseases: Links to Environmental Change

Environmental factors are major contributors to many emerging and re-emerging infectious diseases. Although the pathways and extent of the environmental role are not always fully known, the disease burden and the economic impact can be significantly reduced by improved environmental management.

In recent years new diseases such as Serve Acute Repiratory Syndome (SARS), and newly resurgent familiar diseases such as tuberculosis, have caused suffering, international disruption and alarm. Frequent environmental changes are key factors. Environmental policy sometimes has a crucial role to play in controlling emerging and re-emerging diseases.

Infectious diseases remain the leading cause of death in the world, accounting for about 15 million deaths per year - approximately 25 per cent of total global mortality (Morens and others 2004). The impact is greatest in the developing world (WHO 2003a). In Africa and South Asia, infectious diseases are the underlying cause of two thirds of all deaths, killing mostly children and young adults. Infectious diseases are also a major cause of permanent disability and poor health and well-being for tens of millions of people, hindering economic development and sustainability in many parts of the world.

The economic and social burden of diseases such as malaria is enormous (Sachs and Malaney 2002, WHO 2003a). In addition to the long-term effects, short-term epidemics of emerging or re-emerging infectious diseases, such as SARS in Hong Kong, Taiwan, and Toronto and plague in India, have each cost billions of dollars. These recent epidemics underscore the fact that we live in a worldwide community that is tightly linked, and that all of us are susceptible to the burden of infectious diseases (Morens and others 2004, Weiss and McMichael 2004).

Box 1: Some definitions

Infectious diseases are caused by the invasion and unwanted growth of living organisms within the body.

Infectious disease vectors are agents that transfer pathogens from one organism to another, for instance, mosquitoes that transmit malaria parasites.

Emerging diseases are those that have recently increased in incidence or in geographic or host range (such as Lyme disease, West Nile virus, Nipah virus); that are caused by pathogens that have recently evolved (such as new strains of influenza virus, SARS, drug resistant strains of malaria); or that are newly discovered (such as Hendra virus, Hantavirus pulmonary syndrome or Ebola virus).

Re-emerging diseases are those that have been controlled in the past, but are now rapidly increasing in incidence or geographic range (such as tuberculosis).

Re-emergence typically occurs because of breakdowns in public health measures for previously controlled infections, or as co-infections, such as occur with HIV.

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