Role of Emerging Infectious Diseases

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Krupa Patel Midterm Assignment
Microbiologist and Nobel Prize winner Joshua Lederberg first coined the phrase “emerging infectious diseases” to describe infections that were newly appearing in a population or having existed but rapidly increasing in incidence or geographic range.1 Emerging diseases can be attributed to either true emergence (i.e. a newly appearing pathogen that has not been present), increased recognition (i.e. a pathogen that was present in a population but has only recently been recognized due to improved diagnostic tests\capabilities), and increased incidence of previously recognized diseases mainly due to increased globalization, travel, urbanization, and susceptibility of host population4. When there is a disturbance to the natural environment, for example logging and urbanization, pathogens and reservoirs are disturbed and displaced leading to emergence in the human population and increased infection rates. Many emerging viral diseases are caused by some variety of RNA viruses, which compared to DNA viruses, have a higher susceptibility to mutation. For example, influenza is caused by RNA viruses of the family Orthomyxoviridae and known for strain mutation year after year, thus the need for reformulation of the vaccine for what will hopefully be the most common strains to infect people that particular season. Though the factors responsible for disease emergence can often be recognized, intervention and defense against these diseases has proven to be difficult.

The definition of emerging disease has evolved rapidly over the last few decades. In 1992, the Institute of Medicine released a statement defining “emerging infectious diseases [as] diseases of infectious origin whose incidence in humans has increased within the past two decades or threatens to increase in the near future.2 The IOM definition was too restrictive, not accounting properly for animal and zoonotic diseases and their impact on the public. Even though specific factors for disease emergence can be identified in most cases, not all causes of emerging or re-emerging disease are due to infection alone. There is a perfect trifecta of disease between host, agent, and environment. For a disease to be introduced and maintained in a population, the host has to be susceptible to colonization and infection, the agent has to be infective for the host, and the environment in which host and agent are interacting has to be conducive to providing effective contact between the host and agent. The Black Death of the 14th century killed millions along the Silk Road from Asia to Europe. Roughly one-third of the population of Europe succumbed to Yersinia Pestis carried by fleas that were harbored by rats aboard passenger ships.3 Crowded ships, emerging trade routes, and increased urbanization created a breeding ground for disease, in this case the perfect vector carried the agent which infected a susceptible host. Emerging diseases are commonly recognized with their regard to impact on populations: high morbidity, mortality, or dramatically high incidence of clinical disease. In the case of the Black Death, Y.pestis devastated the world’s population and made its mark in history.

Rarely if ever do emerging diseases occur for no reason. There are a multitude of factors responsible for disease emergence: ecological changes, human behavior, increased travel and globalization, and microbial mutations/adaptations to name a few. Antimicrobial resistance is the ability of a microorganism to resist the effects of an antimicrobial agent either due to intrinsic characteristic, acquired selection for mutation, or by acquisition of a resistance gene from other microorganisms.5 Not only have inappropriate prescribing of broad spectrum antibiotics fostered the growth of resistant organisms, but also widespread misuse of antibiotics by the public. The notion that a pill will cure all disease, even viral infections which should be treated...
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