Microbe-Human Interactions, Infection and Disease
The Human Host
Patterns of Disease: Disease Stages
Epidemiology: The Study of Disease in Populations
Reference: https://sites.google.com/site/rccmicrobiology/chapter-13-microbe-human-interactions-infection-and-disease
- Contact, Infection, Disease --A Continuum
- Infection: condition in which a pathogenic microorganisms penetrate the host's defenses.
- Disease: when cumulative effects of the infection damage or disrupt tissues and organs.
- Infectious disease: disruption of a tissue or organ caused by microbes or their products.
- Resident Flora: The Human As a Habitat
- Normal resident flora: indigenous flora.
- Microflora or commensals.
- Acquiring Resident Flora
- Flora can limit pathogens from growing due to taking up nutrients or antagonism.
- Flora can be a resident of organisms that are pathogenic to others.
- Staphlococcus aureus.
- Initial Colonization of the Newborn
- Uterus is usually sterile free and newborns don't become exposed until the breaking of fetal membranes.
- Within 8-12 hours, newborn is typically colonized by bacteria such as staphylococci and lactobacilli.
- Colonization of intestine depends on if the baby is breast fed or bottle fed.
- Susceptible to infection due to immature immune system.
- Indigenous Flora of Specific Regions
- Flora of the Human Skin
- Flora does not extend to dermis and resides in or on dead cell layers.
- Also, follicles and glands.
- Transition zones: where skin joins with the mucus membranes like the nose.
- Rich in flora.
- Transient flora (exposed flora): clings to skin surface but does not ordinarily grow there.
- Gained through contact.
- Resident population: lives and multiplies in deeper layers of the epidermis and in glands and follicles.
- Notably: staphylococcus, corynebacterium, and propionibacterium. (Also, yeast)
- Flora of Gastrointestinal Tract
- Flora resides inside the lumen or mucous epithelium of the gastrointestinal tract.
- Esophagus undergoes peristalsis, process of wave-like movements, which flushes microorganisms down the esophagus.
- Flora of the Mouth
- Carries most diverse flora.
- Microhabitats include: check epithelium, gingiva, tongue, floor of the mouth, and tooth enamel.
- S. mutans and S. sanguis make a major contribution to dental caries by forming a sticky dextran slime in presence of simple sugars.
- Flora of the Large Intestine
- Coliforms: gram negative, factultatively anaerobic, and lactose-fermenting microbes.
- Present in smaller numbers in large intestine.
- Predominant fecal flora are anaerobic bacteria.
- Many species ferment products that are beneficial to host.
- Skatole: one chemical that gives fecal matter it's stench.
- Intestinal gas is known as flatus and explosion of it is flatulence.
- Some people lose ability to secrete the enzyme lactase.
- Lactose is acted upon by intestinal bacteria instead.
- Flora of Respiratory Tract
- Microorganism common to colonize the upper respiratory tract (nasal passages and pharynx) are oral Streptococci.
- Staphylococci aureus preferentially reside in nasal entrance, nasal vestibule, and anterior nasopharynx.
- Steptococci and Haemophilus seen to colonize the tonsils and lower pharynx.
- Lower respiratory is unfavorable for bacteria to grow.
- Flora of the Genitourinary Tract
- Most flora surrounds vagina and outer opening of urethra and anterior opening of urethra for men.
- Urinary tract infection can easily occur in women since the urinary tract is so short.
- Before puberty, the vagina has a higher pH of about 7 and later lowers to about 4.5.
- Believed to protect the development of the uterus.
- Studies with Germ-free Animals
- Germ-free or axenic have fewer diseases and live longer as long as they are kept in a sterile environment.
- Germ-free animals had a lower immune system and slower antibody response.
- Gnotobiotic: inoculated with single type of microbe or several in an isolated containment to determine characteristics of relationship with host/other microbes.
- True Pathogen
- Capable of causing infection and disease in healthy persons with normal immune defenses.
- Opportunistic Pathogens
- Cause disease when the host's defenses are compromised or when they become established in a part of the body that is not natural to them.
- Levels and Classes of Microbes
- Class 1: not known to cause disease.
- Class 2: moderate risk agents.
- Class 3: readily transmitted and virulent agents.
- Class 4: highest risk, deadly pathogens.
- Virulence factors: properties of microbes to invade a host and produce toxins (toxigenicity).
- Virulence: degree of disease.
- Can be due to single or multiple factors.
- Pathogenicity: ability to cause disease in host.
- Portal of Entry: Gateway to Infection
- Portal of entry: entry of a microbe into the tissues.
- Usually cutaneous or membranous boundary.
- Exogenous: originating from source outside the body (environment, human, or animal).
- Endogenous: already existing on or in the body.
- STORCH: common infections of fetus and neonate.
- Syphilis, taxoplasmosis, other (hepititis B, AIDS, and chlamydia), rubella, cytomegalovirus, and herpes simplex virus.
- Complications of STORCH viruses are spontaneous abortion, congenital abnormalities, brain damage, prematurity, and stillbirths.
- Size of Inoculum
- Infection dose: minimum number for infection to occur.
- Microorganisms with smaller infectious dose have greater virulence.
- Lack of infectious dose will generally not result in infection.
- Once in excess of ID, disease can be extremely rapid.
- Mechanisms of Invasion and Establishment of the Pathogen
- How Pathogens Attach
- Adhesion: process by which microbes gain a more stable foothold at the portal of entry.
- Fimbriae
- Glycocalyx
- Adhesins (ligands) that bind to complementary host recpeptors.
- Biofilm
- Fimbriae
- Bacteria pathogens commonly attach by fimbriae (pili), flagella, and adhesive slimes or capsules.
- Viruses commonly attach by specialized receptors.
- Protozoa can infiltrate by modes of locomotion such as cilia.
- Exoenzymes: extracellular enzymes that breakdown or inflict damage to tissues or dissolve extracellular barriers and penetrate through or between cells to underlying tissues.
- Examples of enzymes:
- Mucinase: digest protective coating of mucous membranes.
- Keratinase: used to digest components of skin and hair.
- Colagenase: digests principle fiber of connective tissue.
- Acts as a coagulate with blood and plasma.
- Streptokinase and Staphokinase do the opposite.
- Dissolve fibrin clots and expediting the invasion of damaged tissue.
- Hyaluronidase: digests hyaluronic acid, the ground substance that cements animal cells together.
- Toxins
- Toxin: specific chemical product of microbes, plants, and some animals that is poisonous to other organisms.
- Function is to damage cell membrane and initiating lysis or disrupting intracellular function.
- Toxigenciity: power to produce toxins.
- Toxinosis: disease caused by toxins produced.
- Toxemia: toxin is spread by blood from the site of infection.
- Intoxication (botulism): disease from ingestion of toxins.
- Toxins named after target of action.
- Neurotoxin: neurosystem.
- Enterotoxins: intestines.
- Hemotoxins: blood.
- Nephrotoxins: kidneys.
- Exotoxin: toxin molecules excreted from cell.
- Proteins produced insde by some bacteria especially Gram +
- Species -specific
- Heat-labile (sensitive)
- Antitoxins are antibodies produced by white blood cells (immunity) to combat exotoxins.
- Toxoid are altered exotoxins which when injected induce immunity.
- Diphtheria extoxin: inhibits protein synthesis.
- Endotoxin: toxin released after a cell is damaged or lysed.
- Lipopolysacharides (LPS): sugar on the outer membrane of gram negative cell walls.
- Gram negative cells sometimes lyse and release LPS into infection site
- Hemolysins: class of bacterial exotoxin that disrupts the cell membrane of red blood cells (and some other cells).
- Causes cells to hemolyze.
- Hemolyze: burst and release hemoglobin pigment.
- Produce unique pattern on blood agar.
- Antiphagocytosis
- Antiphagocytic factors: type of virulence factor used by some pathogens to avoid certain while blood cells call phagocytes.
- Phagocytes: white blood cells that destroy pathogens.
- Leukocidins: substance that kills white blood cells.
- Capsule/Slime: extracellular surface layer that makes it difficult for the phagocyte to engulf them.
- Made of special protein or wax.
- Destroys neutrophils and macrophages.
- Necrosis: accumulated damage to cells and tissues.
- Viruses do not produce toxins, but they multiply in and lyse the cell.
- Paterns of Infection
- Localized Infection: microbe enters body and targets specific tissue.
- Systematic Infection: spreads to several sites and tissue fluids.
- Focal Infection: infectious agent breaks loose from a local infection and carried to other tissues.
- Mixed Infection: several agents establish themselves simultaneously at the infection site.
- Cooperate in breaking down tissue.
- Primary Infection: initial infection.
- Secondary Infection: when the initial infection in complicated by another infection caused by a different microbe.
- Ex: Chicken Pox infected at pox by S. aureus is a secondary infection.
- Needs not be the same infection site.
- Acute Infections: rapid, severe, but short lived effects, infections.
- Chronic Infections: persist over long period of time.
- Subacute Infections:
- -itis: inflamation.
- -emia: blood.
- -osis: indicates the disease they causes.
- -oma: tumor.
Patterns of Disease: Disease Stages
- 1. Incubation period.
- No S&S.
- 2. Prodromal stage.
- Appearance of mild S&S.
- Malaise.
- Not feeling well.
- 3. Period of invasion.
- Illness.
- Maximum S&S.
- 4. Decline.
- S&S declining.
- Fever departs.
- Secondary infection may occur.
- 5. Convalescent period.
- Body repair.
- Recovery.
- Returns to normal health.
- Syndrome: disease that can be defined by a certain complex of signs and symptoms.
- Signs and Symptoms of Inflamation
- Edema: accumulation of fluid in an afflicted tissue.
- Lesion: general term for site of infection or disease.
- Signs of Infection in the Blood
- Change in number of white blood cells.
- Leukocytosis: increase in white blood cells.
- Leukopenia: decrease in white blood cells.
- Septicemia: blood infection.
- microorganism is multiplying in bloodstream in large numbers.
- Bacteremia: small numbers of bacteria in blood.
- Viremia: small number of viruses in blood.
- Infections That Go Unnoticed
- Asymptomatic (subclinical, inapparent): disease where patient experiences no symptoms.
- Respiratory and Salivary Portals
- Coughing or sneezing media from lower or upper respiratory tract.
- Airborne droplets.
- Skin Scales
- Skin lesions can serve as a portal of exit.
- Fecal Exit
- Many helminth worms release cysts and eggs through feces.
- Urological Tract
- Pathogens that infect the kidney.
- STDs.
- Removal of Blood or Bleeding
- Shared needles.
- Blood donation.
- Latency: dormant state of the infectious agent.
- Periodically can become active and produce a recurrent disease.
- Sequelae: long-term or permanent damage to tissues or organs.
Epidemiology: The Study of Disease in Populations
- Terms of Epidemiology
- Notifiable: agencies required by law to collect data (varies by State).
- Communicable: host to host transmision.
- Contagious: extremely efficient host to host transmission.
- Non-Communicable: no host to host transmission.
- Correlation: one factor assumed to be related to another.
- Cause and Effect: one factor is proven to caused a measurable change in another.
- Koch's Postulates
- 1. Microorganisms are isolated from a dead animal.
- 2. Microorganisms are grown in pure culture. The microorganisms are identified.
- 3. The microorganisms are injected into a healthy animal.
- 4. The disease is reproduced in the second animal; microorganisms are isolated from this animal.
- 5. Pathogenic micoorganisms are grown in pure culture. Indentical microorganism identified.
- Sumarized:
- 1. Presence of pathogen.
- 2. Isolate.
- 3. Inoculate.
- 4. Disease.
- 5. Isolation of organism.
- Can Koch's postulates be used for every ethiological agent/pathogen?
- Not ethical.
- Disease may be caused by multiple organisms.
- Many pathogens can't be grown in lab/media.
- Endemic: present constantly in a population.
- Epidemic: a disease suddenly has a higher than normal incidents in a population. (Whooping Cough & West Nile)
- Pandemic: when an epidemic spread worldwide.
- Sporadic disease: occurs randomly & unpredictably.
- "Endemic reservoir but sporadic in population."
- Disease Cycle
- Survival outside the host (reservoir).
- Transmission to host.
- Portal of Entry.
- -----------------------------(no disease above this point)
- Attaches to target tissue.
- Colonization.
- Host damage (signs & symptoms).
- Portal of Exit.
- Incidence: number of new cases.
- Prevalence: the number of infected people at any given time.
- Moridity: the number of disease cases (sick individuals) within a specific time period with respect to the entire population.
- Mortality: the number of disease deaths during a specific time period with respect to the total population. Expressed in deaths per 100,000 people per year.
- Endogenous infections - caused by patient's own oportunists among the microflora.
- Ex: biting nails.
- Exogenous infections - caused by orgnaisms that enter the patient from the environment
- Human Reservoirs
- Asymptomatic carriers.
- Symptomatic carriers.
- Diseases commonly spread by carriers:
- Animal Reservoirs
- 150+ pathogens infect both animals & humans.
- Zoonoses
- Diseases transmitted naturally (directly or indirectly) from infected animals to humans.
- Examples of zoonoses:
- Nonliving Reservoirs
- Soil: Clostridium tetani, C. botulinum, fungi such as ringworm.
- Water: Vibrio cholerae, Salmonella typhi, Giardia
- Food:
- Nosocomial Infections
- Nosocomial infections are diseases acquired during a hospital or health facility stay.
- Urinary tract infections.
- Respiratory infections
- Surgical incisions.
- What are the universal precautions?
- A set of guidelines established by the CDC to reduce the risks of disease
- Divided into three general groups
- Contact Transmission
- Direct transmission requires body contact between individuals (horizontal/vertical transmission).
- Indirect transmission requires fomites (nonliving object that can transmit disease)
- Droplet transmission occurs when a person cough or sneeze dired mucous. Travel less than 1m.
- Vehicle Transmission
- A vehicle is a non-living carrier of a microbe from its reservoir to a host.
- Water, soil, food.
- Vector Transmission
- Vectors are live animals that transmit deases to humans.
- Mechanical Vectors
- Microbes carried outside vector's body.
- Biological Vectors
- Microbes carried inside vector's body (Mosquitoes and malaria).
- No dogs in swimming pools because of Leptospira spirochetes.
- Control of Transmission
- Quarantine: separation of healthy person who has been exposed to a communicable disease.
- Isolation
- Vector control.
Reference: https://sites.google.com/site/rccmicrobiology/chapter-13-microbe-human-interactions-infection-and-disease