Chapter 13 Microbe-Human Interactions: Infection and Disease

Chapter Outline

13.1. The Human Host A. Contact, infection, disease—A continuum 1. Microbes invade the tissues leading to infection 2. Pathologic state that results in damage or disruption of organs or tissues is known as a disease 3. Infectious disease: disruption of a tissue or organ caused by microbes and their products B. Resident biota: The human as a habitat 1. Normal resident biota or indigenous biota 2. Acquiring resident biota a. Human body has wide variety of environmental niches that vary in: i. Temperature ii. pH iii. Nutrients iv. Oxygen tension b. Most areas of the body in contact with the outside environment harbor biota c. Internal organs and tissue, including fluids, are generally microbe-free d. Bacterial biota can benefit the human host by preventing overgrowth of harmful microbes: i. Fermentation of glycogen by lactobacilli keeps pH in vagina very acidic ii. Prevents the overgrowth of the yeast Candida albicans e. Immunosuppression such as AIDS i. Normal biota can lead to infection in these patients ii. Streptococcus pneumoniae and pneumococcal pneumonia f. Endogenous infections can occur when normal biota is introduced into a previously sterile site 3. Initial colonization of the newborn a. First exposure is the breaking of the fetal membranes, when vaginal microbes can enter the womb b. Comprehensive exposure during passage through birth canal c. Large intestine microbiota: i. Bottle-fed infants have coliforms, lactobacilli, enteric streptococci, and staphylococci ii. Breast-fed infants have Bifidobacterium C. Indigenous biota of specific regions: Table 13.3 1. Biota of human skin 2. Biota of the gastrointestinal tract a. Biota of the mouth b. Biota of the large intestine i. Bacteroides, Bifidobacterium, Fusobacterium, Clostridium ii. Small amounts of E. coli, other coliforms 3. Biota of the respiratory tract 4. Biota of the genitourinary tract 13.2. The Progress of an Infection A. Pathogenicity

1-1 1. True or opportunistic pathogens 2. Predisposing factors 3. Virulence and virulence factors B. Becoming established: Step one—portals of entry 1. Infectious agents that enter the skin 2. The gastrointestinal tract as portal 3. The respiratory portal of entry 4. Urogenital portals of entry a. STD (sexually transmitted disease) 5. Pathogens that infect during pregnancy and birth a. TORCH (toxoplasmosis, other such as hepatitis, rubella, cytomegalovirus, and herpes simplex viruses) are the common infections of fetus and neonate C. The size of the inoculum 1. Infectious dose D. Becoming established: Step two—Attaching to the host 1. How pathogens attach (adhesion) (Table 13.6) E. Becoming established: Step three—Surviving host defenses 1. How microbes escape phagocytosis a. Leukocidins b. Slime layer or capsule formation c. Survival inside phagocytes after ingestion F. Causing disease 1. How virulence factors contribute to tissue damage a. Extracellular enzymes (exoenzymes) i. Mucinase ii. Keratinase iii. Collagenase iv. Hyaluronidase v. Streptokinase; Staphylokinase b. Bacterial toxins: A potent source of cellular damage i. Toxigenicity ii. Toxinoses iii. Toxemia iv. Intoxication v. Exotoxin 1. Hemolysins vi. Endotoxin c. Inducing an injurious host response G. The process of infection and disease 1. Establishment, spread, and pathological effects a. Necrosis b. Cytopathic effects of viral infections 2. Patterns of infection a. Localized infection b. Systemic infection c. Focal infection d. Mixed infection (polymicrobial disease) e. Primary and secondary infection f. Acute and chronic infections H. Signs and symptoms: Warning signals of disease 1. Sign

1-2 2. Symptom 3. Syndrome 4. Signs and symptoms of inflammation a. Edema b. Granulomas and abscesses c. Lymphadenitis d. Rash e. Lesion 5. Signs of infection in the blood a. Leukocytosis b. Leukopenia c. Septicemia, bacteremia, viremia 6. Infections that go unnoticed a. Asymptomatic b. Subclinical or inapparent I. The portal of exit: Vacating the host 1. Respiratory and salivary portals 2. Skin scales 3. Fecal exit 4. Urogenital tract 5. Removal of blood or bleeding J. The persistence of microbes and pathologic conditions 1. Chronic infection and latency 2. Sequelae K. Reservoirs: Where pathogens persist 1. Reservoir versus source 2. Living reservoirs a. Carriers i. Asymptomatic carrier ii. Incubation carrier iii. Convalescent carrier iv. Chronic carrier v. Passive carrier b. Animals as reservoirs and sources i. Biological vectors ii. Mechanical vectors iii. Zoonosis 3. Nonliving reservoirs L. The acquisition and transmission of infectious agents 1. Communicable disease 2. Contagious 3. Noncommunicable disease 4. Patterns of transmission in communicable diseases a. Modes of contact transmission b. Routes of indirect transmission c. Indirect spread by vehicles: Contaminated materials i. Vehicle ii. Fomites d. Indirect spread by vehicles: Air as a vehicle i. Droplet nuclei ii. Aerosols

1-3 M. Nosocomial infections: The hospital as a source of disease (fig. 13.14) N. Universal blood and body fluid precautions O. Which agent is the cause? Using Koch's Postulates to determine etiology 1. Identify microbe by evidence in patient 2. Isolate and cultivate microbes 3. Inoculate a suitable test subject 4. Reisolate the agent in test subject 13.3. Epidemiology: The Study of Disease in Populations A. Who, when, and where? Tracking disease in the population 1. Morbidity and Mortality Report (CDC) 2. Epidemiological statistics: Frequency of cases a. Prevalence b. Incidence c. Mortality and morbidity rate d. Endemic e. Sporadic f. Epidemic g. Pandemic

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