Question

Define "emerging pathogen ". Which type of microbes comprise most emerging pathogens today? Why do you think this is?

Answer 1

An emerging pathogen can be defined as the causative agent of an infectious disease whose incidence is increasing following its appearance in a new host population or whose incidence is increasing in an existing host population as a result of long-term changes in its underlying epidemiology

or

An emerging pathogen can be defined as an infectious agent whose incidence is increasing following its first introduction into a new host population;

These pathogen switches from one host species to another (species ‘jumps’) had led to some of the most devastating disease epidemics. Many of the emerging pathogens of greatest concern are pathogenic viruses. The major example of an emerging pathogenic infectious disease is HIV/AIDS, which likely emerged a century ago after multiple independent events in which the virus jumped from one primate host to another (chimpanzees to humans) and subsequently, as a result of a complex array of social and demographic factors, spread readily within the human population. Other examples of disease emergences include SARS, which emerged from bats and spread into humans first by person-to-person transmission in confined spaces, then within hospitals, and finally by human movement between international air hubs. Nipah virus also emerged from bats and caused an epizootic in herds of intensively bred pigs, which in turn served as the animal reservoir from which the virus was passed on to humans. H5N1 influenza emerged from wild birds to cause epizootics that amplified virus transmission in domestic poultry, precipitating dead-end viral transmission to poultry-exposed humans. Ebola virus, MERS virus, Chicken gunya virus are other examples.

The main responsible factors for emergence of pathogens include ecological changes, such as those due to agricultural or economic development or to anomalies in climate ,human demographic changes and behavior, travel and commerce, technology and industry, microbial adaptation and change,  and breakdown of public health measures.  Ecological, environmental, or demographic factors that place people at increased contact with a previously unfamiliar microbe or its natural host promote dissemination. These factors are increasing in prevalence and together with the ongoing evolution of viral and microbial variants and selection for drug resistance, suggests that infections will continue to emerge and probably increase and emphasizes the urgent need for effective surveillance and control.