Tuberculosis

Question 1

First part of the immune system to interact with TB bacilli

Answer 1

Alveolar macrophages

Question 2

Ghon focus

Answer 2

Giant cell granuloma

Question 3

Ghon complex

Answer 3

Regional lymph nodes filled with granulomas, visible on X-ray, MRI, CT

Question 4

Miliary tuberculosis

Answer 4

Tiny foci of granuloma, often appears in lungs, form of disseminated primary infection

This form of TB tends to be lifelong

Characteristic of the disease are tubercles found in many organs, including the liver, spleen, kidneys, brain, and meninges. aseation and cavitation are less frequent than in secondary TB.

Question 5

Characteristic staining used to detect Mycobacterium tuberculosis

Answer 5

Acid-fast

Question 6

Constitutional symptoms of tuberculosis

Answer 6

fever, weight loss, and drenching night sweats.

Question 7

Mycobacterium leprae

Answer 7

• slow-growing, acid-fast bacillus that is the causative agent of leprosy
• illness that ranges between two polar forms: tuberculoid (strong immune response with few organisms) and lepromatous (minimal immune response with immense numbers of organisms)

Question 8

“atypical mycobacteria”

Answer 8

Mycobacteria other than M. tuberculosis

Question 9

Unusual properties of mycobacteria

Answer 9

acid fast, are unusually resistant to drying, and grow slowly compared with most other bacteria.

Question 10

mycolic acid

Answer 10

The most abundant wax within the M. tuberculosis membrane, which confers the property of acid-fastness to the bacteria

Question 11

How acid-fast staining works

Answer 11

Stain w/ fuchsin

Treat with 3% HCl in EtOH

Wrinse

Only mycobacteria should retain the stain, appearing as slender red rods

Question 12

Best ways to kill mycobacteria

Answer 12

• Mycobacterial antiboitics
• Heat (Pasteurization of products kills any hiding mycobacteria!)

Question 13

Pasteurization

Answer 13

60^oC, 30 minutes

Question 14

The generation time of M. tuberculosis is ___ compared with ___ for most bacterial pathogens

Answer 14

The generation time of M. tuberculosis is 15 to 20 hours compared with less than 1 hour for most bacterial pathogens

Question 15

Nearly all persons coinfected with ___ and M. tuberculosis will eventually develop active tuberculosis

Answer 15

Nearly all persons coinfected with HIV and M. tuberculosis will eventually develop active tuberculosis

Question 16

Mycobacterium avium complex

Answer 16

• organism is often found in water and soil and is generally harmless to immunocompetent individuals
• May infect individuals with advanced HIV or AIDS
• Colonizes GI tract, then disseminates
• Fever, malaise, wasting
• Diarrhea, abdominal pain, spleen and liver symptoms, retroperitoneal lymphadenopathy

Question 17

Air in a room occupied by a person with pulmonary TB may remain infectious even . . .

Answer 17

air in a room occupied by a person with pulmonary TB may remain infectious even after the person has left the room

Question 18

TB infection rarely occurs outdoors because ___

Answer 18

TB infection rarely occurs outdoors because ultraviolet light kills M. tuberculosis

Question 19

M. tuberculosis utilizes ___ as a means of transport to other body sites.

Answer 19

M. tuberculosis utilizes macrophages moving through the lymphatics as a means of transport to other body sites.

Question 20

The most important consequence of lymphohematogenous dissemination of TB is . . .

Answer 20

The most important consequence of lymphohematogenous dissemination of TB is seeding of the lung apices

Question 21

Reactivation of TB

Answer 21

• Occurs during periods of immunosuppression
• Lesions of latent TB become necrotic, undergo caseous necrosis, and eventually merge into larger lesions
• With time, the caseous lesions liquefy and discharge their contents into bronchi, creating a well-aerated cavity into which organism may proliferate and seeding new alveoli
• Caseous lesions also serve as sources of droplet nuclei to infect others

Question 22

Caseous necrosis is ___.

Answer 22

Caseous necrosis is unstable

The material it produces tends to liquefy and discharge, especially within the bronchioles of the lung, producing a cavity and providing conditions in which bacteria multiply to very high numbers.

Question 23

The uneasy equilibrium in the war between tuberculosis and macrophages

Answer 23

• Some macrophages successfully kill TB
• Some TB successfully kill macrophages
• Some macrophages capture the TB and wall it off, harboring dormant bacteria for years

Question 24

Caseation and cavitation are phenotypes characteristic of. . .

Answer 24

. . . secondary TB. Usually not primary, primary progressive, or miliary.

Question 25

In tubercular meningitis, . . .

Answer 25

. . . there are actually very few organisms in the CSF, but they are able to cause potent inflammation

Question 26

tuberculin conversion

Answer 26

A newly positive TB PPD test after a history of negative tests

Question 27

About \_\_% of individuals with active TB have negative tuberculin tests.

Answer 27

About **15%** of individuals with active TB have negative tuberculin tests.​ Many of these individuals are immunocompromised, hence the lack of conversion.

Question 28

A false-positive tuberculin test may be caused by . . .

Answer 28

. . . exposure to an atypical mycobacterium

Question 29

An even better test for TB than the PPD

Answer 29

IFNg release assay

Question 30

Pott disease

Answer 30

* When M. tuberculosis affects vertebral bodies. * patients present with chronic back pain * Failure to diagnose and treat Pott disease can result in destruction of vertebrae and permanent disability

Question 31

Initial diagnostic approach for TB

Answer 31

* Careful history * Sputum culture * Chest X-ray

Question 32

The gold standard for TB diagnosis

Answer 32

Culture

Question 33

Radiometric culture techniques

Answer 33

Accelerate the diagnosis by early detection of radioactive CO₂ released by organisms metabolizing ¹⁴C-labeled palmitic acid, providing results within 7 to 14 days. as opposed to the usual ~6 weeks

Question 34

Mycobacteria which may mimic TB but result in much less severe infections

Answer 34

* Mycobacterium avium complex * Mycobacterium kansasii

Question 35

Persons with pulmonary TB usually become noncontagious within ___ of therapy if the organisms are sensitive to the drugs administered

Answer 35

ersons with pulmonary TB usually become noncontagious within **2 weeks** of therapy if the organisms are sensitive to the drugs administered

Question 36

Drugging TB

Answer 36

* Requires multiple drugs to prevent development of resistance for active TB * isoniazid (INH), rifampin, pyrazinamide (PZA), and ethambutol * chemoprophylactic on-site treatment of seroconverters detected via PPD with single dose of isoniazid

Question 37

Why are vaccines against TB no good?

Answer 37

TB requires a cell-mediated immune response, antibodies just bounce right off its waxy coat!

Question 38

Studies of M. leprae are difficult because . . .

Answer 38

. . . the organism cannot be continuously grown in vitro

Question 39

phenolic glycolipid

Answer 39

* A surface lipid of M. leprae, may provide a defense against oxidative killing * To kill M. leprae, macrophages must be efficiently activated by CD4 T cells

Question 40

Leprosy bacilli grow best at . . .

Answer 40

Leprosy bacilli grow best at **low temperatures**

Question 41

Tuberculoid leprosy

Answer 41

* characterized by red blotchy lesions with localized anesthesia on face, trunk, extremities * organisms grow and cause thickening in nerve sheaths. These thickened nerves can be felt through the skin, a characteristic of leprosy * patients usually demonstrate delayed-type hypersensitivity to **lepromin** *

Question 42

Lepromatous Leprosy

Answer 42

* can reduce or suppress specific T cells produced by the host that activate infected macrophages * **In lepromatous leprosy, there is little or no delayed-type hypersensitivity to lepromin** * Both skin and nerves may be involved * With time, the **loss of local sensation** leads to **inadvertent, traumatic lesions** of the face and extremities. These may become secondarily infected, resulting in additional disfigurement.

Question 43

\_\_\_ are at extremely high risk for primary progression of infection after an initial TB exposure and for disseminated disease.

Answer 43

**Children under the age of four** are at extremely high risk for primary progression of infection after an initial TB exposure and for disseminated disease. **Their presentations may be more subtle than in adults** and **classic symptoms may not be present**. **All household contacts should be investigated for TB, even without symptoms.**

Question 44

To treat TB, the classic course is. . .

Answer 44

4 drugs for 2 months, followed by 2 drugs for 4 months

Question 45

When giving someone with reactivated TB an immunosuppressive treatment for a chronic autoimmune condition (like Lupus or sarcoidosis), . . .

Answer 45

. . . it is fine to have them on an anti-TNF, as long as they are on antimycobacterials.

Question 46

Sensitivity of different TB tests

Answer 46

Smear and stain: 5,000-10,000 cfu/mL Gene Xpert (PCR technique): 150 cfu/mL Culture: 10 cfu/mL

Question 47

Generally speaking, someone with a positive TB smear is probably ___ while someone with a negative TB smear is probably not.

Answer 47

Generally speaking, someone with a positive TB smear is probably **contagious** while someone with a negative TB smear is probably not.

Question 48

IFNg RA and PPD are for ___ TB.

Answer 48

IFNg RA and PPD are for **latent** TB. Their results for active TB are uninterpretable.

Question 49

If you are unsure whether to treat someone that is at high risk for having developed TB but does not display symptoms and has negative tests . . .

Answer 49

. . . just start them on isoniazid and repeat testing in a week or two.

Question 50

The four drugs given for TB

Answer 50

RIPE **R**ifampin **I**soniazid **P**yrazinamide **E**thambutol

Question 51

Children and TB

Answer 51

Children \<4 are at risk high for developing TB

Question 52

Generally speaking for HIV patients, if \_\_\_\_, PPD and IFNg release assay are reliable. If \_\_\_\_, they should not be trusted.

Answer 52

Generally speaking for HIV patients, if **CD4\>200**, PPD and IFNg release assay are reliable. If **CD4\<200**, they should not be trusted.