Infectious Dz Flashcards
Exam 3 (182 cards)
What are the 2 types of diagnostic tests?
antibody
organism
What are some advantages of organism testing?
- positive implies presence of organism
- can localize dz from sample
- sensitive in immunocompromised
- quantification may be possible
What are some disadvantages of organism testing?
- dec. sensitivity for some inf. (chronic, smoldering inf)
- false (+)s possible
- positive test =/= disease
- no sense of chronology
Culture (type, pros, cons)
- organism detection
- Pros: organism id + sensitivity testing
- Cons:
- -> false neg from low sample size
- -> some org. un-culturable
- -> transport and storage == death
- -> can be expensive
Immunoassays for antigen (type, pros, cons)
- organism detection
- Pros: n for organism detection, fast and easy (SNAP tests)
- Cons:
- -> false (-) w/ low [antigen]
- -> false (+) w/ cross reaction
- -> variable sens. and specificity
End Point PCR
- only gives + or -
- no level of quantification
Real Time PCR
- quantitative measurement of [DNA] present in sample
Cons of Real Time PCR
- false (-) w/ strain variation
- inhibition of certain enzymes
- potential for false (-) from degradation
- false (+) from contamination
- can detect dead/ inactive organisms
Antibody Detection (pros)
- sensitive as a single test in immunocompetent host w/ chronic dz
- paired serology (IgM/G) allows from chronology
Antibody Detection (cons)
- neg early on acute disease
- neg w/ URT infections
- neg w/ immunocompromised patients
- false (+) are problematic
- poor indicators of treatment success
When do to antibody vs organism?
Organism : acute disease, immunocompromised
Antibody: chronic persistent infection, organisms undetectable
Actinomyces (epidemiology/ etiology)
- does not exist freely in nature
- n oropharyngeal and gi inhabitant
- young adult to middle-aged large breed dogs/ usually immunocompetent
Actinomyces (pathogenesis)
- grass awns in oropharynx penetrate and migrate
- bite wound inoculation
- CNS actinomycosis: hematogenous spread from thorax (abscess)
Diagnosis of Actinomyces or Nocardia
- gram stain (thin, gram (+), filamentous bacteria)
- H&E not effective stain
- alert lab fro culture + mult samples
- Nocardia is variably acid-fast (+) while Actinomyces is acid fast (-)
Treatment of Actinomyces or Nocardia
- prolonged treatment w/ high dose abx to prevent relapse
- drain abscesses or pyothorax first
- Actinomyces: peneclillin is ideal
- Nocardia: much worse prognosis, but TMS
Nocardia (etiology, epidemiology)
- aerobe, ubiquitous soil saprophyte
- 1/3-4 are immunosuppressed
- much less common than actinomyces
Nocardia (pathogensis)
- inhalation –> pulm nocardiosis –> pleural or systemic spread
- hematogenous dissemination to other organs
- skin involvement: firm to fluctuant SQ swellings containing serosanguinous –> purulent fluid
3 major groups of mycobacterium
- Tuberculosis mycobacteria (m. tuberculosis and m. bovis)
- Opportunistic mycobacteria (slow and fast growing)
- Lepromatous mycobacteria
Tuberculous Mycobacteria
- m. tuberculosis and m. bovis
- highly pathogenic
- reverse zoonosis [m. tuberculosis is potentially zoonotic)
Opportunistic Mycobacteria
- saprophytic, survive > 2 years in env.
- slow-growing (m. avium complex)
- rapid-growing (RGM)
- not zoonotic
Pathogenesis of Opportunistic Mycobacteria (slow and RGM)
- multiply intracellularly at inoculation site and local LN
- Avium tend to be disseminated
- Defective cell-mediated immunity –> allows for persistence or dissemination –> granuloma formation
Rapidly-growing Mycobacterium
- inoculated into skin via trauma
- enhance pathogenicity in adipose
- most animals are immunocompetent
- cats are most susceptible (especially female)
Clinical signs of RGM
- cutaneous and subcutaneous granulomas (especially the inguinal area [mycobacterial panniculitis])
Diagnosis of RGM
- Histopath –> pyogranulomatous inflammation
- Isolation:
- -> tuberculous can take 4-6 weeks to grow
- -> RGM may take 3-5 days