ABSTRACT
Diseases emerge when an agent crosses over from another vertebrate species to humans. The mechanisms of that crossover are largely unknown, but some factors seem to facilitate the process, such as poor sanitation, the encroachment of humans on animals' habitats, maintaining food animals in crowded conditions, and extensive use of antimicrobials. The use of antimicrobials to fight disease in humans and animals and promote growth in animals is a well-entrenched practice. Ecological changes such as new agricultural practices, urbanization, globalization and climate change seem to drive microbes from animals into new human hosts. The global marketplace is driven by the market the consumers and their purchasing power. Systems of production of food and biological products have changed dramatically over the last twenty years. The produce and products were often uneven in quality and supply because the production system depended upon many variables there were good years and bad years.
