Host-Pathogen Interactions Flashcards
Examples of host physical and chemical defenses
- skin
- normal flora
- flushing effect (tears, urine)
- GIT (low pH)
- vaginal tract
Portals of entry for the parasite
- resp tract (inhalation)
- GIT (ingestion)
- genital tract (sexual transmission)
- skin (abrasions, bites)
- congenital (vertical)
- other (injections)
Define a reservoir of infection
- where the infectious agent is normally found and where it may multiply or survive
Define a source of infection
May be the patients own flora, animal or environmental source
To cause disease a pathogen must:
- gain access to host
- adhere to host tissues
- penetrate or evade host defenses
- damage the host
How is disease achieved
- adherence
- colonisation
- invasion
Characteristics needed for a pathogen to cause disease
- transmissibility
- survival
- infectivity
Types of pathogens
- primary (neisseria meningitidis)
- opportunistic (staph epidermidis)
Define pathogenicity
Capacity of an organism to cause disease
What determines virulence?
- toxin production (type and amount)
- invasiveness and spread
- immune evasion
Define virulence
The disease-causing properties of a strain of pathogen
Examples of virulence factors in Strep pyogenes
- streptokinase (dissolution of clots)
- DNAses
- streptolysin O
- erythrogenic toxin
What does the M protein do?
- heat and acid resistant
- mediates attachment of bacterium to epi cells
- resists phagocytosis by leukocytes
5 groups of potential bacterial contributors to pathogenesis of infectious diseases
- adhesins
- invasins
- impedins
- aggressins
- modulins
Define adherence
Attachment to the host by the microbe at portal of entry
Describe flagella
- long filaments
- produce motility by rotation
Describe fimbriae or pili
- finer, shorter fragments
- responsible for attachment and adhesion
- sex pili for gene transfer
Mechanisms to overcome anatomical barriers
- production of tissue-damaging exoenzymes
- parasite-directed endocytosis
- phagocytosis of enteropathogenic bacteria by M cells in intestine
Types of spread
- local
- cell-to-cell
- translocation of mac-resistant bacteria to intestine and ingestion by M cells
- lymphogenous or hematogenous generalization
Describe the action of a capsule
- usually polysaccharide material
- impairs phagocytosis
- prevents engulfment and destruction by leukocytes
Mechanisms for antiphagocytosis
- capsule
- phagocyte toxins
- macs disabled by type iii secretion system
- inhibition of phagosome-lysosome fusion
- inhibition of phagocytic oxidative burst
Types of toxins
- exotoxins (secreted by bacteria)
- endotoxins (cell wall)
Symptoms of tetanus
- trismus
- neck stiffness
- difficulty swallowing
- rigidity of abdo muscle
- facial muscle spasm
- back muscle spasm
- generalised tetanic seizures
Types of exoenzymes
- coagulases
- kinases
- hyaluronidase
- collagenase
Mechanisms of immunotolerance
- prenatal infection
- molecular mimicry
Describe superantigens
- gram positive exotoxins
- cause polyclonal T cell activation
- massive cytokine release
