mycobacterium Flashcards
(27 cards)
overview of mycobacterium
cause classic tubercle lung lesions
- M. tuberculosis - highly contagious
- M. bovis - highly contagious
atypical -
M. avium complex (MAC)
Rapidly growing mycobacteria (RGM)
lepromatous mcycobacteria
mycobacterium spp. are acid-fast bacteria
obligate aerobes
non-spore formers
thick, waxy cell wall
mycolic acid binds carbol fuchsin dye
3 possible outcomes after ingestion or inhalation of tubercle bacilli
- if adequate cell- mediated immunity, organisms are killed by activated macrophages
- develop active infection
- disseminate within lung or intestine and spread to other organs - organisms go into latency
- can reactivate - secondary TB
inhalation and ingestion of tubercle bacilli
ingestion: localize to intestine
inhalation: localize to lung –> alveolar macrophages
clinical progression of disease
is VERY SLOW - like months
- insidious onset
- weight loss
- weakness exercise intolerance
= +/- respiratory signs (cough, nasal, discharge
vertical or horizontal transmission
- reparatory secretions
- transplacental
- via milk (pseudo vertical)
tubercle bacilli cause granulomas
granuloma - multinucleated giant cells and epithelioid cells surrounded by T- cells
-immunology of granuloma formation
- multiply inside macrophages
- activated CD4+ T-cells (TH1) - clonal expansion
- cytokine production: IFN-Y, IL-12, IL-2
- recruit more macrophages!
what other organisms have similar pathogenesis?
tubercle bacilli encounter and host range
- both are extremely contagious and zoonotic
reservoir = infected animals or humans
M. tuberculosis
- human - adapted pathogen
- very rare in non-primate
M. bovis
- broad host range
- can infect many animal species
TB is a historic human pathogen
written evidence for disease as long as 3300 years ago in India
- though the organism may be more than 3 million years old
Goes by many names: “phthisis”, “ the white plague”, “consumption”, “captain of all these men of death”
human Tb
very much still around and very much still in AK
Is TB reportable
,,, heeeelllll yeahhhhh
what about tb in wildlife?
yup.
cervids
raccoons, opossoms, coyotes, swine, elephants
in the UK, bovine TB is endemic in badgers
TB surveillance and diagnostics
Routine slaughter inspection
- USDA FSIS (food safety inspection service)
- meat inspection act of 1906
Tissue sent for
- PCR
- culture (takes up to 4 months
Tuberculin skin test
Tuberculin testing in cattle
tests exploits type 4 hypersensitivity response
caudal fold test (CFT)
- m. bovis purified protein derivative (PPD)
- if reactor (+) –> CCT test necessary
comparative cervical fold test (CCT)
- M. Bovis
- M. Avium
reactors may be due to exposure to M, avium
The CFT
testing requirements:
AK: import,export only
CO: all dairy cows every 3 years
MUST BE PERFORMED BY A USDA ACCREDITED VETERINARIAN
MUST BE READ BY THE SAME VETERINARIAN 72 HOURS LATER
ANY REACTION IS SUSPECT
the CCT - THIS IS ON THE EXAM
if a CFT reactor–> separate from the herd, report to state vet
- note that like with Brucella, we don’t call them “positive” at this point!
A cct must be done by a STATE vet or a USDA vet which is NOT equivalent to a USDA accredited vet
size of induration of M. bovis PPD compared to M, avium PPD
lab testing
acid fast stain on a histopathology or cytology
for definitive diagnosis
- APHIS lab in AMES IA
- PCR on lesion tissue
- culture
TB prevention and control
testing as required by regulation
- check you state
- herd quarantine or depopulation
Voluntary testing when acquiring new animals
Don’t drink raw milk
antimicrobial therapy not possible in food animals
- depopulation/slaughter
BCG vaccine
Bacille Calmette-Guerin (BCG)
attenuated M. Bovis strain developed in early 1900’s at institute Pasteur
-for humans
still used in countries with a high TB burden, reduces active TB by 71%
interferes with skin testing in humans
M. avium subspecies
paratuberculosis (MAP)
- Johne’s disease
- cannot replicate in environment
- infected animals are the reservoir
M. avium complex (MAC)
- ubiquitous in the environment
- sporadic problem in poultry and wild birds
- usually only a problem in immunocompromised non avian species
- occasional infections in small children (cervical lymphadenitis)
Johne’s disease review
Dairy cattle» beef cattle
infected as calves
- slow, chronic process
- granulomatous enteritis and wasting
- diagnosed typically when >2 years old
agent shed in feces, colostrum, milk, in utero
can survive but not replicate in the environment
diagnosis by PCR, ELISA, culture (SLOW)
insidious economic effects due to deceased feed efficiency
MAC: M. avium complex
rarely cause infections in domestic animals
sometimes cause infection in exotics/zoo animals
- causes chronic granulomatous disease
assumed to be due to immunocompromise
not considered zoonotic or contagious
rapidly growin mycobacterium (RMG)
environmental
very similar presentation to
-nocardia
-actinomyces
- deep tissue infections, draining tracts
cause pyogranulomatous inflammation
non-contagious
not zoonotic - but tattoo ink?????
common species of RGM
fortuitum
chelonae
smegmatis
marinum
abscessus
RGM diagnosis
actinomyces and nocardia should be on your differentials
histopathology
aerobic, anaerobic, fungal cultures, mycobacterial culture
RGM grow in regular aerobic culture but it is still helpful to order mycobacterial culture
they are rapidly growing…. no shit
- as opposed to OTHER mycobacteria, growth is evident in 3-14 DAYS
- standard aerobic culture only held for 2 days
