Chapter 15 Microorganisms and Human Disease 2004 Wadsworth Thomson Learning Seven Virulence Factors 1 Maintain a reservoir 2 Leave reservoir and enter host 3 Adhere to surface of host 4 Invade the body of the host 5 Evade the bodys defenses 6 Multiply within the body 7 Leave the body and return to reservoir 2004 Wadsworth Thomson Learning
1. Maintain a reservoir Human reservoirs sick individuals healthy carriers incubatory carriers not yet developed symptoms chronic carriers Animal reservoirs zoonosis human disease from animal reservoir Environmental reservoirs soil
water 2004 Wadsworth Thomson Learning 2. Enter a host Portals of entry body surfaces conjunctiva nose
mouth skin urethra vagina placenta Figure 15.2 2004 Wadsworth Thomson Learning Measurements of infection Infectious dose ID50 number of cells required to cause infection in 50% of subjects
Lethal dose LD50 number of cells required to cause death in 50% of the subjects Figure 15.3 2004 Wadsworth Thomson Learning Modes of transmission Respiratory droplets most common method of transmission spread rapidly Fomites
inanimate object Direct contact sexually transmitted diseases kissing, saliva vertical transmission prenatal--across placenta perinatal--during or shortly after birth 2004 Wadsworth Thomson Learning Modes of transmission Fecal-Oral route direct body contact
suspended in air survive drying Parenteral direct entrance blood vessel tissue below the skin mucous membranes arthropod vectors needles or sharp objects 2004 Wadsworth Thomson Learning 3. Adherence to body surface Overcome defense mechanisms
adhesins bind to receptors tissue trophism Figure 15.6 2004 Wadsworth Thomson Learning 4. Invade the body Penetration into cells survive phagocytosis induce endocytosis intracellular pathogens Figure 15.7 2004 Wadsworth Thomson Learning
Invade the body Penetration into tissues beyond entering the cell survival mechanisms rich environment move into blood or lymphatic circulation Figure 15.7 2004 Wadsworth Thomson Learning 5. Evade Bodys Defenses Phagocytosis process where foreign substances are eaten by
specialized cells Capsules mucoid cover essential for pathogenicity in certain strains Surface proteins interfere with contact between cell and phagocyte 2004 Wadsworth Thomson Learning Evade Bodys Defenses Immune system antigenic variation mutations which change surface antigens
IgA proteases enzymes which break down antibodies Serum resistance blocks the complement system a normal defense mechanism to lyse bacteria Obtaining iron tissue has all nutrients except unbound iron siderophores iron-binding proteins secreted by pathogen 2004 Wadsworth Thomson Learning 6. Multiplication and Pathogenesis Growth leads to pathogenesis
Toxins exotoxins endotoxins toxic proteins Damage by host response Viral pathogenesis 2004 Wadsworth Thomson Learning Exotoxins Secreted proteins two subunits A: active B: binding
B subunit attaches to cell component A subunit alters component Figure 15.10 2004 Wadsworth Thomson Learning Exotoxins cholera enterotoxin stimulates intestinal cells to secrete fluid E. coli enterotoxin similar to cholera Tetanus neurotoxin
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