Mycobacterium

Question 1

Characteristics

Answer 1

-slow growing, non motile rods; often generation times greater than 12 hrs

-gram positive but don’t stain

-mostly biocontainment level 2, but mycobacterium tuberculosis is level 3

Question 2

Why do Mycobacterium not stain with Gram’s?

Answer 2

-Presence of mycolic acid- a lipid

-Acid fast- because they retain stain following decolorization with acid alcohol

Question 3

Host or habitat

Answer 3

Host associated but some survival in environment (but atypical)
-M. tuberculosis-respiratory tract, feces, milk, urine
-M. avium subsp paratuberculosis- feces

Question 4

Taxonomy of mycobacterium

Answer 4

-slow growers vs. rapid growers

-non-MTb complex based on pigment production

Question 5

Mycobacterium tuberculosis

Answer 5

-Associated with granulomatous disease

-mostly human disease

-zoonotic infections with other MTb complex= M. bovis common cause of TB in Canada

Question 6

Mycobacterium bovis clinical signs

Answer 6

-associated with disease in humans and ruminants

-destructive lesions: granulomatous caseating lesions

Several forms:
1. no outward clinical signs- only found with surveillance
2. Generalized- emaciation, lethargy, weakness, anorexia
3. Respiratory- chronic, intermittent, moist cough

Question 7

Transmission of Mycobacterium bovis

Answer 7

-nose to nose contact

-ingestion of contaminated feed/water

**long incubation period with period of latency

Question 8

Suspicion of a case of Mycobacterium bovis

Answer 8

-Quarantine- movement restrictions

-Investigation- history, vet records, Tuberculin skin tests +IFN gamma blood test, Necropsies on positive animals

-Humane depopulation

-Cleaning and disinfection

-Compensation- CFIA pays compensation of market value of animals destroyed

Question 9

Intradermal tuberculin skin test

Answer 9

-very sensitive, less specific
*dont want false negatives! Too risky!

-delayed type hypersensitivity (Type IV)-positive animals will have swelling

-cell mediated immunity - in positive animals see swelling develop over 24-72hrs

Question 10

IFN gamma blood test

Answer 10

-less sensitive, very specific
*identify false positives

-blood collected from those who react to tuberculin test

-expose WBCs in blood to antigen, measure production of cytokine as a response

Question 11

Mycobacterium bovis wildlife populations

Answer 11

1. Wood bison in Northern Alberta and NWT
2. Elk in Riding Mountain National Park in MB

**in european badgers in UK/Ireland, bushtail possums, wild boars in spain

Question 12

Mycobacterium avium supsp. paratuberculosis

Answer 12

-causes Johne’s disease in cattle and other ruminants

-slow progressive disease (mths to yrs)
*no clinical signs in animals under 2yrs old

-worldwide distribution, not treatment and no vaccines

Question 13

Clinical signs of Johne’s disease

Answer 13

Chronic contagious granulomatous enteritis
-persistent diarrhea
-weight loss
-debilitation
-animals not usualy febrile or depressed

Thickening of distal small intestine characteristic lesion

**50% of animals can be subclinical

Question 14

Mycobacterium lepraemurium

Answer 14

causes Feline leprosy
-chronic
-singular or multiple nodules
-cutaneous lesions (head, neck, forelimbs)
-more common in coastal area

Question 15

Treatment for Feline leprosy

Answer 15

*from mycobacterium lapraemurium

Treat:
1. Surgical excision
2. Adjunctive antimicrobials

Question 16

Mycobacterium leprae

Answer 16

-causes leprosy in humans
*thought to have genetic predisposition

-slowly progressing disease of skin, peripheral nerves, eyes, upper respiratory tract

-associated with armadillo contact in Americas

-easily treated with antimicrobials

Question 17

Sample collection

Answer 17

M bovis
-lymph nodes, lung tissues, other lesions

M avium subsp paratuberculosis
-feces, ileal lymph nodes, blood

M. lepraemurium
-tissue biopsies

Question 18

Lab ID

Answer 18

1. Intradermal testing
2. Culture- very slow
3. PCR
4. Acid fast stained smears
5. Serology
6. Histology

Question 19

When do you see false positives with intradermal testing?

Answer 19

-cross reactivity with other Mycobacterium spp

-vaccinations- huge challenge and why we don’t vaccinate in Canada

Question 20

Why do we see false negatives in intradermal testing?

Answer 20

-improper handling or reagents or improper testing procedure

-must be licensed by CFIA to perform test

Question 21

Zoonoses

Answer 21

-Mycobacterium spp have broad host range and should be zoonotic

-organisms of particular concern= Mycobacterium tuberculosis complex (M. bovis is most relevant in N. America)

-Mycobacterium bovis responsible for 2% TB cases in US.. transmission through contaminated and unpasteurized dairy OR contact with infected tissues while hunting

-Mycobacterium avium associated with HIV patients

-Mycobacterium lepraemurium not zoonotic

-Mycobacterium avium subsp. paratuberculosis-associated with Crohn’s disease

Question 22

Treatment options

Answer 22

-susceptibility testing done by agar dilution

-Agriculture animals-antimicrobial therapy not done

-Companion animals- polypharmacy necessarily to prevent resistance development
*need species level ID. check for intrinsic resistance