|
List of Infectious Diseases
Contents
An understanding of the biological basis for how pathogens cause disease and the immunological basis of resistance to pathogenic microorganisms requires insight into several basic factors that together direct the initiation and outcome of pathogenic infections. The interaction of pathogens with the host is frequently thought to consist of three stages, namely, entry and colonization of the microorganism in host tissue, pathogenic invasion and growth in host tissues along with the elaboration of toxic substances, and the inflammatory response of the host. These stages reflect the more traditional concepts of infection (presence of pathogen in a host) and disease (reaction to the infection). Even though these terms are often used interchangeably, when signs and symptoms of disease are present, the term disease and not infection should be used. Signs refer to responses measurable in both animals and humans, such as temperature increases, whereas symptoms indicate being able to report how one feels during illness and are thus limited to humans beyond infancy (perhaps excepting crying and other nonverbal indications infants have of indicating distress. Many organisms may infect an individual without causing significant disease, hence the need for distinguishing between infection and disease. It is interesting that many bacterial factors that causes diseases in mammals also cause disease in plants, worms, fungi, and fruit flies. Toxin elaboration is one of the best-characterized molecular mechanisms of microorganism pathogenesis, while host factors such as interleukin-1 (IL-1) and interleukin-6 (IL-6), TNF-α, kinins, inflammatory proteins, products of complement activation, and mediators derived from arachidonic acid metabolites (leukotrienes) and cellular degranulation (histamine) readily contribute to the severity of disease. The interplay of these factors will dictate the severity of the disease, which may range from mild to severe even among individuals infected with the same microorganism. One of the major functions that attenuate the course of disease is host immune responses, which often account for the discrepancy in disease severity among different individuals.
Bacteria with Unusual Morphology
Protozoan and Helminth Parasites
|
click the animation to read more about the featured organism
|
Congenital CMV
