Micro: PCP, Toxo, MAC in AIDS

Question 1

What is a normal CD4 count?

Answer 1

450-1400

Question 2

What are the 3 major clinical syndromes in pts w AIDS?

Answer 2

pulmonary - dyspnea and infiltrates (PCP most common)
neurologic - focal findings and mass lesion (toxo)
fever of unknown origin (FUO) - disseminated infections (MAC)

Question 3

CXR has diffuse intersitial infiltrates what should you expect?
CXR has lobar infiltrate what should you suspect?

Answer 3

PCP (ground glass infiltrates)

s. pneumoniae

Question 4

What is the phylogenetic status of PCP?

Answer 4

was believed to be parasite

it is actually a fungus

Question 5

What is the microbiology of PCP?

Answer 5

2 prominent antigen groups, includes MSG complex

Question 6

What is the life cycle/pathogenesis of PCP?

Answer 6

developmental stages: small pleomorphic trophozoite and cyst form (up to 8 intracystic bodies)
probably sexual phase
asexual replication by trophic form and sexual by cyst
MSG facilitates adherence to ECM, surfactant and mannose
MSG undergoes antigenic variation

Question 7

What is the pathology of inf w PCP?

Answer 7

heavy airless lungs, thickened alveolar septa, foamy eosinophilic alveolar exudate w parasites
organism doesn’t invade lung tissue

Question 8

How is PCP diagnosed?

Answer 8

CXR, PC in bronchopulmonary secretions by sputum or bronchoalveolar lavage
transbronchial or open lung biopsy may be necessary
LM: Giemsa stains nuclei of trophozoites, silver stains cyst walls, DFA, clusters of crushed ping pong balls
elevated LDH (up to 500)
+ beta-D-glucan
oxygen desaturation when exercising
PaO235 indicate severe dz and need for steroid treatment

Question 9

What is the treatment for PCP?

Answer 9

high dose TMP-SMX (also used for prophylaxis if cd4 <200, once HAART raises this, can stop prophylaxis)
as organisms die can deteriorate due to dead contents filling alveolar spaces - combo w prednisone

Question 10

What is the transmission of P. jiroveci?

Answer 10

person to person is rare

thought to be inhaled

Question 11

What are lung symptoms that do NOT indicate PCP and necessitate search for a different dx?

Answer 11

lymphadenopathy
pleural EFFUSIONS (PCP can have pneumothorax)

Question 12

What are signs of a poor prognosis for PCP?

Answer 12

pts who AREN’T immunocompromised

pts who present w pneumothorax

Question 13

What is the microbiology and basic life cycle of t. gondii?

Answer 13

obligate intracellular parasite
oocyst, trophozoite/tachyzoite, and bradyzoite forms
oocyst released into environment, develops four sporozoites which are ingested to cause infection
sexual and asexual phases (asexual in body responsible for dz = tachyzoites and bradyzoites)

Question 14

What is the reservoir of infection for t. gondii?

Answer 14

cats - only definitive hosts for sexual stages

Question 15

What are the different modes through which humans can become infected w t. gondii?

Answer 15

eating undercooked meat w cysts
ingestion of oocyst from fecally contaminated hands or food
organ transplant or blood transfusion
transplacental
accidental inoculation of tachyzoites

Question 16

What does t. gondii do in the body?

Answer 16

gets into phagosome and prevents fusion w lysosome, differentiates into tachyzoite and divides rapidly
form cysts in skeletal muscle, myocardium, brain

Question 17

What are the features of persistent infection w t. gondii?

Answer 17

dormant stage = bradyzoite

persistent inf w bradyzoites in immunocompetent, upon immunocompromise, cysts can reactive & cause symptoms

Question 18

What are the clinical manifestations of toxo?

Answer 18

usually asymptomatic in immunocompetent
encephalitis in HIV+
congenital can be severe

Question 19

How is toxo diagnosed?

Answer 19

serology - positive IgM in immunocompetent
AIDS - IgG+ on SERUM (IgM not helpful), ring enhancing lesion, PCR of CSF (negative doesn’t rule out)
usually improve w/i 10-14 days of rx, otherwise biopsy
tachyzoites on histology

Question 20

What is the treatment of toxo?

Answer 20

not necessary in immunocompetent, not pregnant
for HIV/AIDS - sulfadiazine w pyrimethamine and leucovorin, continue until lesions and CD4 improve
CD4 less than 100 need TMP-SMX prophylaxis if IgG+

Question 21

What is the microbiology of MAC?

Answer 21

slow growing, non-pigmented in culture

isolated from birds, fresh and salt water

Question 22

What is the pathophysiology of MAC?

Answer 22

inhaled into respiratory tract, ingested into GI
translocates across mucosal epithelium, infects macrophages in LP and spreads lymphatically to local nodes
spreads hematogenously in immunocompromised

Question 23

What are the clinical presentations of MAC?

Answer 23

immunocompetent: pulm dz
infects those w CF
in HIV: disseminated dz presents as nonfocal fever syndrome

Question 24

What are the three different kinds of pulm dzs that occur in immunocompetent individuals w MAC?

Answer 24

elderly smokers (men) w pre-existing lung dz (COPD) - chronic cavitary pneumonia that resembles tb
elderly non-smoking females - mild lingular or RML infiltrates, productive cough and weight loss
single pulmonary nodule

Question 25

What are the features of disseminated dz of MAC?

Answer 25

fever, night sweats, weight loss
lymphadenopathy, pancytopenia
abnormal liver fxn tests, watery diarrhea, RUQ pain

Question 26

How is MAC diagnosed?

Answer 26

culture for AFB

DNA probe can differentiate from tb

Question 27

What is the treatment for MAC?

Answer 27

either azithromycin (preferred) or clarithromycin +
ethambutol and rifamyin (rifabutin has less interxns w HAART than rifampin) +
HAART

Question 28

What is the prophylaxis for MAC?

Answer 28

azithromycin

not needed w CD4 above 100