MBioCh14

• etiology: study of cause of disease
• pathogenesis: development of disease
• infection: colonization of body by pathogen
• infectious disease: can be transmitted from one individual to another

• communicable disease: can spread from one host to another
• noncommunicable dissease: not transmitted from one host to another
• contagious disease: easily spread from one host to another

• signs: change in body that can be measure or observed (fever, rash)
• symptoms: change in body function felt by the host
• syndrome: specific group of signs and symptoms that accompany a disease

• sporadic disease: occurs only occasionally in a population (Typhoid fever)
• endemic disease: constantly present in a population (common cold)
• epidemic disease: acquired by many hosts in a given area in a short time (influenza)
• pandemic disease: worldwide epidemic (AIDS)

• acute disease: develop rapidly and lasts only a short time (influenza)
• chronic disease: develops slowly, less severe but lasts for a long time (TB, hep B) - typically more fatal
• subacute disease: intermediate between acute and chronic (sclerosing panencephalitis)
• latent disease: period of no symptoms when the pathogen is inactive (shingles

• local infection: limited to a very small area of the body (boils, abscesses)
• systemic infection: infection throughout body (measles)
• focal infection: systemic infection that began as local infection (gets into blood stream)

• bacterermia: bacteria in blood stream
• septicemia: multiplication of pathogens in the blood stream
• toxemia: toxins in blood
• viremia: viruses in blood

• primary infection: actue infection that causes initial illness
• secondary infection: opportunistic infection after a primary (predisposing) infection; more serious
• subclinical infection: no noticeable signs or symptoms (inapparent infection)

• Incubation period: (no signs or symptoms) Time from which you are infected to when symptoms begin
• Prodromal period: (mild signs or symptoms) Begin to show signs/symptoms
• Period of illness: (most severe signs/symptoms) Sick, immune system kicks in
• Period of decline: (signs and symptoms) Occurs if body overcomes pathogen
• Period of convalescence: body returns to normal (days to weeks)

• Normal microbiota compete with pathogens to prevent overgrowth/infection
• Compete for nutrients, space (competitive exclusion - C. difficile completely line the GI tract so pathogens literally cannot attach)
• Produce substances harmful to invader (acids or bacteriocins)

• Symbiosis: living together of two different organisms
• Commensalism: one organism benefits with the other is unaffected (Staphylococcus epidermidis on the skin)
• Mutualism: both organisms benefit (E. coli bacteria in the large intestine)
• Parasitism: one organism benefits while the other is harmed (H1N1 virus)

• Normal microbiota
• Reside permanently in/on body [FOR LIFE]
• Normally do NOT produce disease
• Are aquired young (lactobacilli from vag, breathing, breast feeding, etc)
• Transient microbiota
• Present for a while then disappear [DAYS to YEARS]
• Normally do not produce disease (unless they go where they "aren't supposed to")
• Acquired from being kissed, touched, etc

Normal microbiota do not causes disease in their normal habitat, but do so when in a different environment (Streptococcus epidermidis on skin is no big, but in cuts = you're fucked)

• Nose
• throate
• lungs
• any air-exposed part of body
• eye
• mouth
• skin
• large intestine (MANY)
• small intestine (few)
• urinary tract
• reproductive system

• Benefits
• Protects host by microbial antagonism (competitive exclusion)
• Synthesize B vitamins and K vitamins for host (we can't)
• Stimulate immune response (keeps it "sharp")
• Dangers
• Opportunism (cause disease in different habitat)
• Microbial synergism (two microbes act together to produce a greater effect eg. Streptococci and periodontal pathogens)

• Short urethra in females
• Inherited trades (sickle cell gene)
• Climate and weather (common cold)
• fatigue (stress)
• age (very young and very old are most susceptable)
• lifestyle
• chemotherapy
• antibiotic therapy

• CONTACT
• Direct: requires close association or physical contact
• Indirect: spread by means of fomites
• Droplets: discharged from sneezing, coughing, etc
• VEHICLE - Transmission by inanimate reservoir
• Waterborne: sewage contaminated water
• Foodborned: incompletely cooked, poor storage, unsanitary conditions
• Airborne: droplets, dust, dirt
• VECTORS - Arthropods carry pathogens from one host to another
• Mechanical transmission: houseflies (typhoid fever, bacillary dysentery)
• Biological transmission: mosquitoes (malaria)

• Direct contact: patient to patient, staff ot patient, visitors to patient
• Indirect contact: fomites, hospital venitalation system
• Nosocomial infections can be prevented by use of aseptic techniques, education about infection control, hand washing, and use of isolation rooms/wards

• Remove reservoirs
• Water purification
• Vector control (insect, rodent, arthropod)
• Isolation
• Treat carriers
• Safe sex
• Proper food handling
• Hand washing (#1)

• Koch's postulates demonstrate that a specific pathogen cause a specific disease
• 1. Microorganisms are isolated from a diseased or dead animal
• 2a. The microorganisms are grown in pure culture
• 2b. The microorganisms are identified
• 3. The microorganisms are injected into a healthy laboratory animal
• 4. Disease is reprooduced in a laboratory animal
• 5a. The microorganisms are isolated from this animal and grown in pure culture
• 5b. Microorganisms are identified (must be same as 2b)

• Some causative agents cannot be cultured on existing articifical media (viruses, Micobacteria lepriae)
• Some diseases are not clear-cut (various pathogens causing similar signs and symptoms)
• Some pathogens may cause several disease conditions
• Infecting humans with infections agents is unethical, may not be pathogenic in other organisms

• Reservoir of infection: continual source of pathogens
• Living
• Human: harbor and transmit pathogens to others; carriers (AIDS, gonorrhea)
• Animal: carry pathogens that causes disease in humans (rabies, lyme disease)
• *Zoonoses - animal diseases that may be transmistted to humans
• NONLIVING
• Soil: fungal (mycoses); bacterial (botulism, tetanus)
• Water: cause gastrointestinal infections (cholera, amoebic dysentary)
• Food: inadequately cooked, improperly prepared, or stored (Tricinella, food poisoning)

• Susceptibility of host (broken skin, compromised immune system)
• Microorganisms in hospital environment (reservoirs for pathogens, patients/staff/visitors, hospital microbes tend to be more resistant to drugs)
• Chain of transmission (direct contact between patients and staff, fomites)

• Endogenous: patients themselves (touching a cut)
• Exogenous: staff, visitors, or other patients

• Urinary tract infections
• Surgical site infections
• Lower respiratory tract infections
• Bacteremia transmitted primarily by IV catheterizations
• Cutaneous infections
• Other

• epidemiology: Study of where and when diseases occur
• descriptive epidemiology: collection and analysis of data (mapped occurrence of cholera to a specific well in London)
• analytical epdimediology: comparison of a diseased group and a healthy group (improved sanitation decreased incidence of epidemic typhus)
• experimental epidemiology: controlled experiments (handwashing decreased incidence of puerperal fever)