Perspectives of public health laboratories in emerging infectious diseases

Chua, Kaw Bing; Gubler, Duane J

Traditionally, emerging infectious diseases are broadly defined as infections that: (i) have newly appeared in a population; (ii) are increasing in incidence or geographic range; or (iii) whose incidence threatens to increase in the near future. 6, 17 Six major factors, and combinations of these factors, have been reported to contribute to disease emergence and re-emergence: (i) changes in human demographics and behavior; (ii) advances in technology and changes in industry practices; (iii) economic development and changes in land use patterns; (iv) dramatic increases in volume and speed of international travel and commerce; (v) microbial mutation and adaptation; and (vi) inadequate public health capacity. 6, 17 From the perspective of public health planning and preparedness for effective emerging infectious disease surveillance, outbreak investigation and early response, the above working definition of emerging infectious disease and its associated factors that contribute to infectious disease emergence are too broad and generic for more specific application and for the development of a national public health system, especially in the context of a public health laboratory system in a country. Thus, in this article, emerging infectious diseases are divided into four categories based on the nature and characteristics of pathogens or infectious agents causing the emerging infections; these categories are summarized in Table 1 . The categorization is based on the patterns of infectious disease emergence and modes leading to the discovery of the causative novel pathogens. The factors or combinations of factors contributing to the emergence of these pathogens also vary within each category. Likewise, the strategic approaches and types of public health preparedness that need to be adopted, in particular with respect to the types of public health laboratories that need to be developed for optimal system performance, will also vary greatly with respect to each category of emerging infectious diseases. These four categories of emerging infectious diseases and the factors that contribute to the emergence of infectious diseases in each category are briefly described below. [18] [19] [20] [21] [22] [23] Factors that contributed to the occurrence of emerging infectious diseases in this subcategory include population growth; urbanization; environmental and anthropogenic driven ecological changes; increased volume and speed of international travel and commerce with rapid, massive movement of people, animals and commodities; and deterioration of public health infrastructure. Subcategory 1b includes known and unknown infectious agents that occur in new host 'niches'. Infectious microbes/ agents placed under this subcategory are better known as 'opportunistic' pathogens that normally do not cause disease in immunocompetent human hosts but that can lead to serious diseases in immunocompromised individuals. The increased susceptibility of human hosts to infectious agents is largely due to the HIV/acquired immune deficiency syndrome pandemic, and to a lesser extent, due to immunosuppression resulting from cancer chemotherapy, antirejection treatments in transplant recipients, and drugs and monoclonal antibodies that are used to treat autoimmune and immune-mediated disorders. A notable example is the increased incidence of progressive multifocal leukoencephalopathy, a demyelinating disease of the central nervous system that is caused by the polyomavirus 'JC'