Polymicrobial Diseases of Animals and Humans

Abstract

Polymicrobial diseases in animals and humans are induced by polyviral infections, polybacterial infections, polymicrobial infections involving viruses and bacteria, polymicrobial infections involving fungi and parasites, and polymicrobial infections as a result of microbe-induced immunosuppression. They are serious diseases whose etiologic agents are sometimes difficult to diagnose and treat. Five common mechanisms of disease pathogenesis exist. First, physical, physiologic, or metabolic abnormalities and stress predispose the host to polymicrobial disease. Second, one organism induces changes in the mucosa that may favor the colonization of others. Third, microorganisms or their products trigger proinflammatory cytokines to increase the severity of disease, reactivate latent infections, or favor the colonization of other microorganisms. Fourth, organisms may share determinants among each other, which give them the ability to damage tissue. Finally, one organism can alter the immune system, which allows the colonization of the host by other microorganisms. Many areas of study in polymicrobial diseases are in their infancy, and the author hopes that this chapter will stimulate interest and work in this evolving field.