Transcript Document
– Microbiota are microbes that reside in the body without causing disease (in symbiosis). • In mutualism, both host and microbe benefit. • In commensalism, the microbe benefits and the host is unaffected. • Pathogens differ in their ability to cause disease. – In parasitism, pathogens cause damage and disease in the host. – Pathogenicity refers to a microbe’s ability to enter a host and cause disease. • Virulence is the degree of pathogenicity. – Pathogenicity islands refers to gene clusters responsible for virulence. • Several events must occur for disease to develop in the host. – An exogenous infection occurs if a pathogen breaches the host’s external defense and enters sterile tissue. – An endogenous infection occurs if normal microbiota enter sterile tissue. – Opportunistic infections occur when commensals take advantage of a change in the body’s environment that favors the microbe. – Primary infections occur in otherwise healthy bodies. – Secondary infections occur in a body weakened by a primary infection. – Local diseases are restricted to a single area. – Systemic diseases disseminate to organs and systems. 19.2 Establishment of Infection and Disease • Diseases progress through a series of stages. – Signs, symptoms, and syndromes characterize diseases. – The incubation period is the time between entry of the microbe and symptom appearance. – The prodromal phase is a time of mild signs or symptoms. – The acme period (climax) is when signs and symptoms are most intense. – As signs and symptoms subside, a period of decline occurs. – The body systems return to normal during the period of convalescence. • Breaching the host barriers can establish infection and disease. – Invasiveness is the ability of a pathogen to penetrate tissues and spread. – Many pathogens use phagocytosis by body cells to enter cells or pass through defenses. • Some staphylococci produce coagulase to form a blood clot that protects them from phagocytosis. • Others produce streptokinase, which dissolves fibrin clots and allows dissemination of the bacteria. • Hyaluronidase enhances pathogen penetration through tissues. • Leukocidins disintegrate neutrophils and macrophages. • Hemolysins dissolve red blood cells. • Virulence can be enhanced in biofilms because immune cells cannot reach bacterial cells. – Toxoids are toxins whose toxicity has been destroyed but still elicit an immune response. – Endotoxins are released upon disintegration of gram-negative cells. • They cause blood coagulation. • Endotoxin shock may occur with antibiotic treatment of diseases caused by gram-negative bacilli. 19.3 Infectious Disease Epidemiology • Epidemiologists often have to identify the reservoir of an infectious disease. – Reservoirs are places in the environment where a pathogen can be found. – Carriers have recovered from the disease but continue to shed the disease agents. • Epidemiologists have several terms that apply to the infectious disease process. – Communicable diseases are contagious. • They are transmittable among hosts in a population. – Noncommunicable diseases are not easily transmitted to another host. • They are acquired directly from the environment. • Infectious diseases can be transmitted in several ways. – Direct contact methods involve close or personal contact with an infected person. – Indirect contact methods can involve fomites. • Nosocomial infections are serious health threats within the health care system. – Health care-associated infections (HAIs) occur as a result of receiving treatment for another condition. – Nosocomial infections are associated with hospitals. • Infectious diseases continue to challenge public health organizations. – Globalization means that diseases emerging anywhere in the world can be spread globally. – Zoonoses are diseases transmitted from other vertebrate animals to humans.