Chapter 14 Flashcards
pathogenicity
ability to cause disease
pathogenesis
steps or mechanisms involved in the development of a disease
infectious disease
- a disease caused by a microbe (a pathogen)
- infection is a common synonym
infection
- colonization by a pathogen
- the pathogen may or may not cause disease
why infections don’t always occur (8)
- microbe in a site where it can’t multiply
- pathogen is unable to attach to receptor sites
- antibacterial factors may be present at site
- indigenous microbiota may inhibit growth
- indigenous microbiota may produce antimicrobial factors to destroy pathogen
- nutrition and health status may result in poor pathogen outcome
- person may be immune to pathogen
- phagocytes may be present in blood
phases in course of disease
- exposure to pathogen
1) incubation period
2) prodromal period (feel bad but not sick yet)
3) period of illness
4) convalescent period (or disability or death)
localized infection
- disease may remain localized or spread
- pimples, boils, abscesses
systemic (generalized) infection
- when the infection spreads throughout the whole body
- TB
acute disease
- rapid onset and rapid recovery
- measles, mumps, influenza
chronic disease
- slow onset and lasts a long time
- TB, leprosy, syphilis
subacute disease
- comes on more suddenly than chronic but less suddenly than acute
- bacterial endocarditis
symptom
- evidence of disease experienced by the pt
- aches, pain, nausea, dizzy, blurred vision
signs
- objective evidence of a disease
- abnormal heart sounds, high pulse, lab results
symptomatic disease
pt experienced symptoms
asymptomatic disease
pt does not experience symptoms
latent infection
- go from being symptomatic to asymptomatic to symptomatic
- not getting reinfected but goes into dormant stage
- syphilis, herpes, shingles
stages of syphilis
1) primary - 3 wks after exposure, painless chancre
2) secondary - 4-6 wks after exposure, rash develops but heals after 12 months
3) latent - no symptoms, may last lifetime
4) tertiary - 5-20 yrs after exposure, CNS and cardio symptoms (sometimes death)
primary infection
first disease
secondary infection
second disease
example of primary and secondary infection
- viral respiratory infection damages epithelial cells
- epithelial cells unable to clear opportunistic bacteria
- opportunistic bacteria cause secondary infection of bacterial pneumonia
steps in pathogenesis of infectious diseases
1) entry of pathogen into body
2) attachment of pathogen to tissues
3) multiplication of pathogen
4) invasion or spread of pathogen
5) evasion of host defences
6) damage to host tissues
virulence
used to express the degree of pathogenicity
virulent vs avirulent
- virulent can cause disease
- avirulent can’t cause disease
virulence examples
- toxigenic C diphtheria can cause diphtheria (virulent), nontoxigenic cannot (avirulent)
- 10 shigella cells to cause shingellosis but 100-1000 salmonella cells to cause salmonellosis, shigella more virulent than salmonella
- some Streptococcus progenies more virulent than others
- some staphylococcus aureus more virulent than othres
virulence factors
- attributes than enable pathogens to attach, escape destruction, or cause disease
- they are phenotypic characteristics
- adhesins (ligands) and pili
adhesins (ligands) virulence factor
- molecules on surface of bacteria that enable pathogens to be recognize and bind to host cell receptors
pili viruence factor
- enable bacteria to attach to surfaces like tissues
obligate intracellular pathogens
- pathogens that must live within host cells in order to survive and multiply
- rickettsia and chlamydia
intraleukocytic pathogens
- live within WBCs cause diseases like ehrlichiosis and anaplasmosis
intraerythrocytic pathogens
- live within RBCs
- plasmodium app that cause malaria and babes spp that cause babesions
facultative intracellular pathogens
capable of intracellular and extracellular existence
intracellular survival mechanisms
- cell wall composition that resist digestions (M. TB)
- prevention of fusion of lysosomes with phagosomes
- production of phospholipase that destroy phagosome membrane
- other unknown mechanisms
capsules
- virulence factor
- streptococcus pneumonias, klebsiella pneumonias, haemophilus influenza, neisseria meningitidis
flagella
- virulence factor
- enable bacteria to invade aqueous areas of body
- may also help to escape phagocytes
major mechanisms by which pathogens cause disease
exoenzymes or toxins they produce
exoenzymes (7)
- necrotizing enzymes that cause necrosis
- coagulase that cause clotting
- kinases that break up clots
- hyaluronidase that breaks down hypotonic acid for movement
- collagenase that breaks down collagen
- hemolysins that break down host RBC, alpha has green halo beta has white halo
- lecithinase that breaks down phospholipid cell membrane causing tissue damage
toxins
- poisonous substances released by pathogens
- endotoxins and exotoxins
endotoxins
- part of cell wall of gram - bacteria
- can cause adverse physiologic effects like fever and shock
exotoxins
- poisonous proteins secreted by pathogens
- neurotoxins, enterotoxins (GI), exfoliative toxin (scalid skin syndrome), erythrogenic toxin (scarlet fever) and leukocidins (destroy WBC)
antigenic variation
- changing surface antigens
camouflage and molecular mimicry
- conceal their foreign nature by coating themselves with host proteins
destruction of antibodies
- produce IgA protease that destroys some of hosts antibodies
mechanisms by which pathogens escape immune response
- antigenic variation
- camouflage and mimicry
- destruction of antibodies
