Micro Bio- Ch. 15

Signs

• Changes in body measured or observes because of a disease

Symptoms

• changes in body function, felt by a patient

Syndrome

specific group of signs and symptoms with a disease

Asymptomatic, subclinical

no signs or symptoms

Infectious disease

• caused by direct effect of pathogen

Contagious

• easily and rapidly spread from one host to another

Communicable disease

• spread from person to person through direct/ indirect mechanisms

Iatrogenic diseases

contracted as the result of medical procedure/ treatment

Nosocomial diseases

acquired in hospital setting

Zoonitic disease

• animals to humans

noncommunicable disease

• disease that is not transmitted from one host to another

Noninfectious disease

• noncommunicable infectious diseases not caused by pathogens

Periods of disease: incubation period

• interval between initial infection and first signs and symptoms, pathogens begin multiplying

Periods of disease: Prodromal period

• short period after incubation, early, mild symptoms, pathogen continues multiplying, host will react

Periods of disease: Period of illness

• disease is most severe

Periods of disease: period of decline

signs and symptoms subside, # of pathogens decrease

secondary diseases possible

Periods of disease: period of convalescence

• body returns to prediseased state, no pathogen

Acute disease

symptoms develope rapidly

disease lasts for short time

Ex. influenza

Chronic disease

symptoms develop slowly

pathologic changes occur over loner time spans

Latent disease

casual pathogen goes dormant for periods of time

no active replication, but then activates and produces symptoms

Pathogenicity

ability of a microbial agent to cause disease

Virulence

degree to which an organism is pathogenic

Avirulent

not harmful

Less virulent pathogens

more likely to result in mild signs and symptoms/asymptomatic

Highly virulent pathogens

almost always lead to a disease state, some may cause multi organ and body system failure

dependent on route of transmission

Median infectious dose (ID50)

number of pathogens required to cause active infection in 50% of inoculated populations

Median lethal dose (LD50)

number of pathogens or amount of toxin required to kill 50% of inoculated populations

infective does for individual varies

• route of entry

• age

• health

• immune status

Bacillus anthracis

• Portal of Entry (ID50)

• Skin: 10-50 endospores

• Inhalation: 10,000-20,000 endospores

• Ingestion: 250,000-1,000,000 endospores

For steps of pathogens

• exposure (contact)

• adhesion (colonization)

• invasion

• infection

portals of entry

portals of entry: Mucous membranes

• lining respiratory tract, gastrointestinal tract, genitourinary tract and conjunctiva -most accessible

portals of entry: skin

impenetrable by most microorganisms

portals of entry: parenteral route

• cut on skin

• directly into tissues when barriers are penetrated

Streptococci portals of entry

• inhaled: pneumonia

• ingested: no signs/symptoms

Adhesion

capability to microorganism to attach to host

capsules

slime layers

biofilms

Invasion

dissemination of a pathogen throughout local tissues or the body

different factors: virulence factors

exoenzymes: used to combat

toxins

Coagulase

• coagulates (clot) fibrinogen:

• fibrin clot may protect bacterium from phagocytosis

Kinases

• digest fibrin clots formed by the body to isolate the infection

Hyaluronidase

• digests polysaccharides that hold cells together, spreading infection

Collagenase

• degrades collagen in connective tissue to promote spreading

IgA proteases

destroys IgA antibodies (critical in mucosal immunity)

Infection: local

limited to small area of the body

Infection: focal

localized pathogen or toxins it produces can spread to a secondary location

Infection: Systemic

infection disseminated throughout the body

Primary infection

acute infection that causes initial illness

Secondary infection

opportunistic infections after a primary infection

Bacteremia

bacteria in blood

toxemia

toxin in the blood

viremia

viruses in blood

Septicemia

bacteria present and multiplying in the blood

Septic

patients with septicemia

Shock

life threatening decrease in blood pressure that prevent cells and organs from receiving enough oxygen and nutrients

• some bacteria release toxins which can lead to low blood pressure

Portal of exit: respiratory tract

• coughing, sneezing

• tuberculosis, pneumonia, smallpox and influenza

Portal of exit: Gastrointestinal tract

feces

• salmonellosis, cholera, typhoid fever, shigellosis, amebic dysentary

saliva

• rabies

Portal of exit: genitourinary tract

• urine and vaginal secretions

• STD

portal of exit: skin

ringworm, herpes simplex and warts

portal of exit: blood

arthropods that bite

• yellow fever, plague, tularemia and malaria

portal of exit: needles or syringes

• aids

• Hep B

Toxin

poisonous substances produced by microorganisms that assist in their ability to invade and cause damage to tissue

toxigenicity

ability of a microorganism to produce a toxin to cause damage to host cells

Toxemia

presence of toxin in hosts blood

Intoxications

presence of toxin without microbial growth

Exotoxins and Endotoxins

based on mode of action

• neurotoxin

• cytotoxin

• enterotoxin

Endotoxins

• produced by gram negative

• apart of outer membrane

  • Lipid A (lipopolysaccharides)

• fever: yes

• Neutralized by antitoxin: no

• LD 50: relatively large

Test to detect endotoxins

Limulus ameobocyte lystate (LAL)

• blood cells (ameobocytes) of horseshoe crab (limulus polyphemus) mixed with patients serum

• ameobocytes react with endotoxin

• observed through chromoenically (color) or coagulation (clotting)

Enzyme linked immunosorbent assay (ELISA) uses antibodies to detect endotoxin

Exotoxin

• mostly gram positive

• by product of growing cell

• made of protein

• no fever

• can be neutralized by antitoxin

• small LD50

types of exotoxins

• intracellular targeting

• membrane disrupting toxins

• superantigens

Intracellular targeting toxin

• targets host cell

• A-B toxin

  • B subunit binds to cell membrane

  • A unit connects

  • enters cell through endocytosis

  • units separate

  • A→ cytoplasm

Membrane disrupting toxin

• lyses host cells by

  • making protein channels in plasma membrane

    • Leukocidins- kills White Blood Cells

    • Hemolysins- kills Red Blood Cells

    • Streptolysins- Hemolysin produced by streptococcus

  • disrupts phospholipid bilayer

Superantigens

• causes intense immune response due to release of cytokines from host cells

• overstimulation of host immune system: distracts body from pathogen

• excessive cytokines in blood causes: fever, nausea, vomiting, diarrhea, shock, death