Zoonoses and Today

By Satesh Bidaisee, Associate Professor of Public Health and Preventive Medicine, St. George's University
August 1, 2011

Since the beginning of human existence, health challenges to individuals and populations have formed an integral and never ending component of life. In the earliest times, health challenges were in the form of injuries from adverse environmental conditions and aggressive interactions between and among fellow humans. While this basic ecologic framework of human pathology applies today, the consequences of human interaction with the environment and its components have evolved parallel with the physical, biological and chemical components of the very same environment.

Before World War 1, British and American public health officials correlated tuberculosis in dairy cattle with severe infections in milk drinking children. The Mycobacterium was traced in municipal milk supplies together with the mapping of the infected animals. Similar to other zoonotic diseases such as Bovine Spongiform Encephalopathy (BSE), bovine tuberculosis blurred the boundaries between urban and rural, production and consumption, and human and animal bodies. As civilizations grew over the centuries, the dynamics of human populations changed and animals assumed a domestic role in mainstream society. The concept of a zoonotic health challenge became significant as it manifested itself in the form of infectious diseases resulting in the great plagues in history but was only recognized by the advent of microbiology and the microscope.

Today, lifestyle diseases are the most common cause of mortality and the pathogenesis, prevention and control of these adverse health conditions are known and very possible. The six leading killers of Americans are coronary heart disease, stroke, lung cancer, colon cancer, diabetes and chronic obstructive pulmonary diseases. These diseases can be prevented with efficient strategies to deal with risk factors like smoking, alcohol, physical inactivity and western diet. However, the future threats of epidemic and pandemic, emerging and re-emerging zoonotic diseases pose serious health challenges. The general population is a natural focus area for zoonotic disease knowledge as pets occupy an esteemed place in many households, often being treated as members of the family. However, the absence of pets will do very little to prevent exposure to zoonotic diseases as the animals and the diseases they can transmit are readily found in the environment humans occupy.

Also, humans may be inadvertently exposed to veterinary vaccines by means of unintentional inoculation or other routes of exposure. The potential for both exposure and for adverse consequences secondary to exposure to veterinary vaccines may be growing. Xenotransplantation, the transplantation of nonhuman animal tissue into humans has resulted in an unquantifiable risk that the use of animal grafts will unleash new zoonoses that can challenge public health.

Knowledge of the extra-human reservoirs of these pathogens is therefore essential for undertaking the epidemiology and control of human disease. Understanding the extra-human life cycles and predicting zoonotic disease outbreaks also informs control activities by targeting several points in the cycle of the pathogen to prevent
human exposure.

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