Lecture Bauman Chap 14 PDF

CHAPTER 14 – INFECTION, INFECTIOUS DISEASES, AND EPIDEMIOLOGY I. MICROBE/HOST RELATIONSHIPS A. Terminology - Symbiosis - Mutualism - Commensalism - Parasitism - Pathogen B. Normal Micro...

CHAPTER 14 – INFECTION, INFECTIOUS DISEASES, AND EPIDEMIOLOGY I. MICROBE/HOST RELATIONSHIPS A. Terminology - Symbiosis - Mutualism - Commensalism - Parasitism - Pathogen B. Normal Microbiota (AKA Normal Flora, Indigenous Microbiota) C. Opportunistic Pathogens Normal Flora may become harmful if an opportunity to do so arises. 1. Introduction into an unusual site in the body 2. Immune suppression 3. Elimination of microbial antagonism II. INFECTIOUS/DISEASE PROCESSES Infection = growth of microorganisms in the host (does not always lead to injury) Disease = injury significant enough to interfere with the normal functioning of the body A. Reservoirs of Infection 1. Animal Reservoirs 2. Human Carriers - individuals who harbor pathogens and spread them to others a. Asymptomatic b. Incubation c. Convalescent d. Chronic e. Passive 3. Nonliving Reservoirs B. Stages of Infection 1. Entry - “Portals of Entry” vary by microbe and include the skin, mucous membranes of the gastrointestinal, respiratory, and urogenital tracts, and the placenta 2. Adhesion - many microorganisms have surface structures (“ligands”) that bind to complementary receptors on animal cells - Examples: Fimbriae, Flagella, Glycocalyces, Viral Spikes 3. Colonization and Growth - initial inoculum is rarely sufficient to cause disease - pathogen must survive host defenses and grow within tissues C. Manifestations of Disease 1. Symptoms - subjective characteristics that can only be felt by the patient 2. Signs - objective manifestations of disease that can be observed by others 3. Syndromes - a group of symptoms and signs that collectively characterizes a disease D. Virulence Factors of Infectious Agents - enable pathogens to enter a host, adhere to host cells, gain access to nutrients and escape detection or removal by the immune system 1. Extracellular Enzymes a. Collagenase - produced by Clostridia that cause gas gangrene - breaks down collagen network that supports tissues b. Hyaluronidase - produced by Streptococci, Staphylococci, and Clostridia - breaks down hyaluronic acid (“tissue cement” that holds animal cells together) c. Coagulase - produced by pathogenic Staphylococci - causes fibrin material to be deposited on organisms, protecting them from host attack d. Kinases - produced by Streptococci and Staphylococci - break down blood clots allowing subsequent invasion of damaged tissues CLINICAL CORRELATION FOLLICULITIS (pages 554 - 556) - usually caused by Staphylococcus aureus - Gram (+) coccus - highly tolerant to salt, extreme temperature and drying - spread by contact with infected individuals or fomites - infection of hair follicle → pimple, furuncle or carbuncle - coagulase causes fibrin to be deposited - leukocidin causes pus production 2. Toxins a. Exotoxins - proteins produced by some bacterial species and released extracellularly - highly toxic (can be fatal in small doses) - highly specific as to “target cell” affected (neurotoxins, enterotoxins, nephrotoxins, etc.) - can stimulate immune system to produce antitoxins - inactivated exotoxins (toxoids) can be used in immunization  CLINICAL CORRELATION – EXOTOXIN MEDIATED DISEASES STAPHYLOCOCCAL DISEASES - caused by Staphylococcus aureus strains that produce various exotoxins - SCALDED SKIN SYNDROME (pages 556 - 557) - release of exfoliative toxin → red wrinkled skin → large blisters over entire body → epidermis peels off in sheets - STAPHYLOCOCCAL FOOD POISIONING (page 725) - heat-stable enterotoxin → nausea, vomiting, diarrhea, cramping lasting ≤ 24 hours - associated with improperly refrigerated or undercooked food contaminated by with normal flora of food preparers - TOXIC SHOCK SYNDROME (pages 751 – 755) - release of toxic shock syndrome toxin → sudden onset fevers, chills, vomiting, diarrhea, extremely low blood pressure, mental confusion and severe red rash - associated with tampon use SCARLET FEVER/SCARLATINA (page 674) - caused by lysogenized strains of Sreptococcus pyogenes - - Gram (+), Catalase (-) cocci - viral DNA codes for erythrogenic (pyrogenic) toxin → fever, pink-red rash and “strawberry tongue” DIPHTHERIA (pages 675 - 677) - caused by lysogenized strains of Corynebacterium diphtheriae - Gram (+) pleomorphic rods in V-shapes and palisade arrangement - phage DNA codes for diphtheria toxin which interferes with protein synthesis by blocking an elongation factor necessary for translation → cell death and widespread organ damage - diagnosis is based on presence of pseudomembrane in throat - - treatment = administration of antitoxin & antimicrobials to kill C. diptheriae - - prevention – administration of DTaP vaccine PERTUSSIS/WHOOPING COUGH (pages 685 - 689) - caused by Bordatella pertussis - Gram (-) coccobacillus that releases pertussis toxin - initial signs and symptoms resemble common cold, progresses to recurrent violent cough in unimmunized children CHOLERA (pages 721 - 723) - caused by Vibrio cholerae - Gram (-), curved rod - endemic in areas with poor sanitation - shellfish harvested from waters contaminated with human feces are also implicated - cholera toxin activates adenyl cylase in epithelial cells of intestine - adenyl cyclase converts ATP to cAMP - cAMP stimulates secretion of electrolytes into intestinal lumen - water follows electrolytes via osmosis → major sign: “rice-water stool”  b. Endotoxins - Lipid A component of LPS in outer cell wall layer of gram (-) bacteria - cell-bound, released in large amounts only when cells lyse - cause non-specific symptoms: - fever - diarrhea - vomiting - toxicity is much lower than exotoxins, but can cause death in very large doses 3. Antiphagocytic Factors a. Capsules b. Leukocidins E. The Movement of Pathogens Out of Hosts - Portals of Exit include: - aerosols from respiratory system - fecal matter - vaginal discharge and semen - infected urine - blood - skin cells F. Modes of Infectious Disease Transmission 1. Contact Transmission a. Direct Contact Transmission - involves body contact between hosts b. Indirect Contact Transmission - pathogens are spread from one host to another by fomites c. Droplet Transmission - droplet nuclei exit body during exhaling, coughing and sneezing and travel less than one meter before encountering next host 2. Vehicle Transmission a. Airborne Transmission - spread of pathogen farther than one meter via an aerosol b. Waterborne Transmission c. Foodborne Transmission 3. Vector Transmission a. Biological Vectors - participate in pathogen’s life cycle b. Mechanical Vectors - merely transport pathogens CLINICAL CORRELATION – INSECT TRANSMITTED DISEASES ROCKY MOUNTAIN SPOTTED FEVER (pages 566 - 567) - caused by Rickettsia rickettsia - Gram (-) rod-shaped intracellular parasite - transmitted by various species of ticks - signs and symptoms: fever, chills, headache, and muscular pain followed by a rash throughout the body (including hands and soles of feet) - rash legions merge and become necrotic PLAGUE (pages 638 - 640) - caused by Yersinia pestis - Gram (-) rod - endemic in rodents, spread to humans by flea bite - two clinical manifestations: - Bubonic Plague - organisms multiply at the bite site and become concentrated in regional lymph nodes → “buboes” - septicema occurs when organism spreads from bubo into bloodstream - virulence factors cause DIC, subcutaneous hemorrhage, necrosis and gangrene → “Black Death” - mortality rate = 50% without treatment - Pneumonic Plague - Y. pestis cells spread from the bloodstream to the lungs or are inhaled - large amounts of bloody sputum are emitted - mortality rate = nearly 100% without treatment LYME DISEASE (pages 640 - 643) - caused by Borellia burgdorferi - Gram (-) spirochete - the most prevalent tick-borne disease in the U.S. - signs and symptoms: acute headache, backache, chills, fatique, and a large “bull’s-eye” rash at the bite site - if not treated properly, may progress to a chronic stage characterized by numbness of limbs, severe exhaustion, visual disturbances, facial paralysis and seizures MALARIA (pages 654 - 657) - caused by a protozoan of the genus Plasmodium - RBC parasites that carry out part of their life cycle in humans and part in Anopheles mosquito - endemic in areas where mosquito breeds - disease is characterized by recurrent fever and chills, severe headache, jaundice, and vomiting and diarrhea - control is via elimination of mosquito breeding grounds, use of insecticides, mosquito netting and protective clothing and antimalarial drugs - over 1 million deaths/year worldwide  G. Classification of Infectious Disease 1. Communicable Diseases - passed from host to host - “contagious” = easily spread 2. Noncommunicable Diseases - acquired from normal flora or non-living environmental reservoir III. EPIDEMIOLOGY = the study of the transmission, incidence, and frequency of disease A. Disease Statistics 1. Incidence = the number of new cases of a disease in a given area or population during a given period of time 2. Prevalence = the total number of cases, both new and already existing, in a given area or population during a given period of time B. Frequency of Disease 1. Endemic - diseases constantly present in a population or in a certain geographical region 2. Sporadic - disease occurs only occasionally 3. Epidemic - sudden outbreak of disease in a particular population 4. Pandemic - worldwide epidemic C. Healthcare Associated (Nosocomial) Infections - infections acquired by patients or health care workers while they are in health care facilities 1. Exogenous - caused by pathogens acquired from the health care environment 2. Endogenous - normal flora organisms become opportunistic pathogens as a result of hospitalization or medical treatments 3. Iatrogenic - result from the use of catheters, invasive diagnostic procedures, and surgery 4. Superinfections - may result from the use of antimicrobial drugs that eliminate microbial antagonism