Nature of Disease Introduction - Definitions Normal Bacteria & Host Koch’s Postulates Patterns of Disease Spread of Infection Nosocomial Infections

Disease - Introduction l Pathogens - disease causing with special properties that permit host invasion l Disease - when microorganism overcomes host defenses; an abnormal physiological state l Pathology - the study of disease

Disease - Introduction l Infection - invasion & growth of pathogen in host; systemic vs. localized l Pathogenesis – the study of the development of disease l Etiology – the study of the cause of disease

Disease - Normal Bacteria l Animals - germ free in utero but are colonized almost immediately after birth l Different bacteria are normally associated with different parts of body l Transients - microorganisms that may occasionally be found associated with the host

Disease - Normal Bacteria l Skin – S. epidermidis/S. aureus l Gastrointestinal Tract –Gram negative bacteria (large intestine) – Streptococcus. mutans (mouth) l Genito-Urinary Tract – Lactobacillus

Disease - Normal Bacteria l Antagonism - normal bacteria prevent growth of others l Bacteria and host have symbiotic relationship (living together) l Three types of symbiosis –Commensalism (one benefits) –Mutalism (both benefit) –Parasitism (one benefits & other harmed) l Opportunistic - do not cause disease normally

Disease - Koch’s Postulates l Etiology or cause established using Koch’s postulates –same pathogen present in every instance of disease –pathogen isolated in pure culture –isolated pathogen causes disease when reintroduced into a healthy host –pathogen re-isolated from the now diseased host

Disease - Patterns l Predisposing factors make hosts more susceptible & include: –age –gender –climate –level of fatigue –nutrition

Disease - Patterns - Development l Incubation period - time between infection & first signs l Prodromal period - first mild signs l Illness period - period when all symptoms are present l Decline period l Convalescence period

Disease - Spread of Infection l Reservoirs of Infection –a continuing source of infection l Reservoirs include: –Human - people who have disease or are carriers (infected but no symptoms) –Zoonoses - wild or domestic animals that transmit disease to humans –Nonliving - soil & water

Disease - Spread of Infection l Transmission –Direct contact –Fomites - inanimate objects –Droplet - saliva, mucus coughing or sneezing –Medium - food, water air –Airborne - carried > 1 meter –Arthropod - insect vectors

Disease - Nosocomial Infection l Acquired during hospitalization or a stay in other health care facilities l Occurs at 5-15% l Can be normal organisms introduced into wrong part of body during invasive procedures l Opportunitic drug resistant G-, e.g. Pseudomonas

Disease - Nosocomial Infection l Compromised host –burns –wounds –immune suppressed (disease or drugs) l Chain of Transmission –Direct contact –Fomites

Disease - Nosocomial Infection l Control –Aseptic techniques –Proper cleaning storage –Maintenance –Properly trained staff l Problems –Multiple drug resistance –Nonuse of effective cleaning agents –Training of staff