Micro

Question 1

coccidiodes

Answer 1

• thermal dimorphes (mold/spherule) endemic to SW US
• high morbidity; low mortality
  
  • 60% mild: flu with clearance/ contained by CMI
  • moderate: valley fever/ desert rhematism (pulmonary + EN)
  • severe: major pneumonia or desseminiation (bare or in PMNs)
• RFs: age, race, immunocomp (pregnancy), job
• Dx: history, PPD, biopsy for spherules, serology for dissemination
• Tx: azoles (if comorbid), fluconazole (meningitis), AmphoB (pregnant or disseminated)

Question 2

erythema nodosa

Answer 2

delayed cell-mediated HSR to fungal antigens→ red tender nodules on exterior surfaces

• immunogenic complication of granulomatous disease
• means risk of dissemination is low

Question 3

histoplasma

Answer 3

• therma dimorph (mold/intracellular yeast); soil-based (bird and bat poop; “spelunker’s disease”); endemic to OH, MI, MS river valleys
• low dose fungus flu: innate immunity kills/ contains in granulomas→ EN
• high dose= TB-like; CMI deficient disseminates in PMNs to mucocutaneous sites
  
  • pancytopenia and ulcerations on tongue
• ​Dx: history, biopsy for yeast in PMNs
• Tx: itraconazole (serious lung), fluconazole (meningitis), AmphoB (disseminated)

Question 4

blastomyces

Answer 4

• thermal dimorph (mold/yeast); broad based budding yeast endemic to E. US
• innate immunity destroys conidia; yeasts harder to kill (BAD1)
• immunocomp or pulm disease predisposes hematogenous spread
  
  • pneumonia: high fever, chills, cough w/sputum, pleuritic pain
  • moderate acute: pneumonia and sputum
  • moderate chronic: TB-like
  • severe acute: ARDS
  • EN or ulcerating skin lesions (dermatiditis)
• ​Dx: cultures (sputum, lesion, suppurating granuloma)
• Tx: itra/fluconazole, AmphoB if severe

Question 5

paracoccidiodes

Answer 5

• thermal dimorph (mold/multibud yeast); endemic to rural S.A.
• semi-opportunistic
  
  • severe in children/ immunocomp
  • moderate in adults (men in agriculture/consulting); long latency
• Dx: pus or tissue KOH
• Tx: itraconazole, AmphoB and combine with treatment for correction of anemia, improved diet, rest smoking cessation, EtOH use

Question 6

thermal dimorphs

Answer 6

• coccidioes: spherules
• histoplasma: yeast in PMNs
• blastomyces: broad based budding yease
• paracoccidiodes

Question 7

opportunistic pulmonary fungal infections

Answer 7

• seldom dangerous without specific predispositions (prolonged neutropenia, uncontrolled HIV or diabetes, profound T cell suppression)
• cryptococcus: MC meningitis in HIV, yeast w/wide capsule, crag (latex agglutination)
• aspergillosis:“peace sign” septate hyphae
• mucormycosis: uncontrolled DM (ketoacidosis), Fe overload, immunocomp (leukemia); nonseptate hyphae w/90 degree angles; ribbon-like
• fusarium: banana macroconidia

Question 8

cryptococcosis

Answer 8

• MC form of meningitis in HIV
• widespread environmental; inhalation from pigeon droppings
• infection originates in lung but clears or progresses to meningitis
• patient presents late in disease with meningitis and skin nodules, or pulm symptoms
  
  • organ damage by tissue distortion from growing yeast; crytococcomas→ focal neuro defects
• Dx: biopsy, CSF (yeast w/wide capsule), crag (latex agglutination)
• Tx: azoles + ampho B; + flucytosine; fluconazole for LT suppression in AIDS

Question 9

aspergillosis

Answer 9

• ABPA: HSR to infection complicating astham, CF; Tx: inhaled sterois + itraconazole
• Aspergilloma: colonizing fungus ball compliating cavitary lung disease; air crescent on scan; Tx: itraconazole + surgery
• CNPA: mimics TB; Tx: voriconazole + AmphoB
• Invasive: most severe, profound immunocomp→ respiratory distress, MI, hemorrhage; Dx: halo sign on scan (small hemorrhage), biopsy (hyphae branching at acute angles “peace sign”); Tx: voriconazole + AmphoB

Question 10

mucormycosis

Answer 10

• mucor or rhizopus→ v. rare deadly invasive vasculitis by environmental mold
• invades brain from sinuses→ infarction; black pus
• RF: uncontrolled DM (ketoacidosis), Fe overload, immunocomp (leukemia)
• Dx: biopsy nonseptate hyphae w/90 degree angles; ribbon-like
• Tx: AmphoB + aggressive surgical removal of disease

Question 11

fusarium

Answer 11

• ubiquitous environmental mold via sinus or wound; infection is rare but fatal
• mycotoxicosis: contaiminated grain
• local infection: burns, prosthetics, contaminated contact lens solution
• disseminated infection: fungemia→ skin lesions; due to prolonged neutropenia, HSCT recipients
• Dx: blood culture (banana macroconidia); histology to differentate from asperillus
• Tx: aggressive surgery, AmphoB, voriconazole

Question 12

mycobacteria characteristics

Answer 12

• gram stain poorly; acid-fast; v. slow growing (2-3 wks)
• virulence factors
  
  • obligate aerobe (grow in lung apex); most important
  • mycolic acid: resistant to desiccation and chemicals
  • cord factor
  • phosphatides: caseating necrosis

Question 13

mycobacteria pathogenesis

Answer 13

• almost always to lung by inhalation; hematogenous spread to lymph, kidney, bones, CNS; GI by swallowing infected sputum
• healthy host rases strong CMI: intracellular infection of naive PMN→ CD4 activate PMN that clear it→ CD8 cells kill infected PMN and establish caseating granulomas→ latency for decades, reactivates with immunosenescence/ suppression
  
  • TNFa also important for containment

Question 14

classic pulmonary TB

Answer 14

• cough, weight loss, fever, night sweats, hemoptysis, chest pain
• cavitary lesions: indicate advanced infection, assc w/ high bacterial load
• noncalcified round infiltrates look like carcinoma vs. calcified nodules of old infection
  
  • xray may look normal if HIV+

Question 15

extrapulmonary TB

Answer 15

• CNS: high inflammation meningitis→ brudzinski’s sign
• Miliary: hematogenous spread→ tiny noncalcified foci of infection in lung (more likely to develop after primary infection)
• Pediatric: must be recently acquired (trace source), watch for miliary and meningitis; culture from gastric lavage (can’t cough hard enough to bring up sputum)
• scrofula: painless enlarging lymph nodes
• skeletal: Pott’s disease in spine
• GI
• GU

Question 16

TB: Dx, Tx, and Prevention

Answer 16

• Dx: determine exposure by TST and/or IGRA
  
  • PPD: type IV HSR; + indicated exposure NOT activate infection
• erform Abx resistance testing as soon as cultures grow (2 wks to culture, 3 more for resistance)
• isolate patient for first 2 weeks in negative pressure
• Tx: DOTS with 4+ drug courses featuring isoniazid
• BCG vaccine (live attenuated M. bovis) used abroad; can create a weak false positive TST

Question 17

MOTT

Answer 17

• atypical environmentally-aquired mycobacteria; do not cause TB or leprosy
• cutaneous infection in healthy host; scrofula in children; systemic in immunocomp
• group 1 photochromogens: m. kansasii, m. marinum (tropical fish enthusiast w/ cutaneous granuloma)
• group 2 scotochromogens: m. scrofulaceum
• group 3 nonchromogens: m. avium/ m. intercellulare→ indistiguishable from TB in severely immunocomp
• group 4 rapidly growing: m. fortuitum, m chelonei, m abcessus, m. smegmatis

Question 18

M. leprae

Answer 18

• obligate intracellular (can’t culture); slowest growing human pathogen with extremely long incubation period; transmission with nasal discharge
• tuberculoid: paucibacillary, vigorous CMI (lepromin +) contains infection and damages peripheral nerves;
• lepromatous: multibacillary, weak CMI (lepromin -), extensive cutaneous lesions
• Dx: lepromin PPD: tests anti-leprosy immunocompetence NOT exposure (unlike TB PPD)
• Tx: 2yrs dapsone + rifampin

Question 19

bacterial pneumonias

Answer 19

• pseudomonas
• chlamydia
• atypicals: legionella, c. burnetti, mycoplasma

Question 20

pseudomonas

Answer 20

• gram-, strict aerobe (non fermenter); oxidase+, grows easily; capsule
  
  • p. aeruginosa: common, serious, MC presents in hospital; green pyocyanin in culture; no flowers in burn units
    
    • endocarditis in IVDA, otitis externa in hot tubs, osteochondritis in sneaker punctures, corneal infections under contacts
  • b. cepacia: common, serious, MC presents in CF centers
  • b. pseudomallei: rare; previously ill travelers/ immigrants from vietnam; weaponizable
  • b.mallei: rare; previously ill travelers/ immigrants with animal handling history; weaponizable
• extreme abx resistance from low permeability outer membranes, efflux pumps
• can present as septicemia/ pneumonia with poor prognosis
• Dx: culture and gram stain
• Tx: test sensitivity before and during treatment

Question 21

chlamydia

Answer 21

• small, obligate intracellular bacterium
• rugged elementary bodies (infectious) unpack into reticulate bodies (replicating) after infection; reticulate bodies form inclusions (T3SS) visible on microscopy, binary fission→ reticulate bodies and later elementary bodies
• c. pneumonia: potential cause of walking pneumonia
• c. trachomatis: several human diseases; MC bacterial STD; tissue culture in rape
• c. psittaci:“parrot fever”: fever is MC symptom, v. contagious→ hepatitis
• Tx: tetracycline (doxycycline) EXCEPT pregnant/ pediatric/ allergic

Question 22

legionella

Answer 22

• poorly staining gram-; opportunistic facultative intracellular
• aspiration or inhalation of contaminated water (cooling towers and whirlpools)
• survives endocytosis by monos and PMNs by altering endosomes so it can multiply in them and escape
• pontiac fever: flulike, no complications
• legionnaire’s disease: life-threatening pneumonia; RF= >55y.o. smoker
• Dx: BOTH urine antigen (detects LP1 strain) and culture of respiratory secretions
• Tx: levofloxacin, azithromycin, erythromycin

Question 23

c. burnetii

Answer 23

• small coccus to short rod, zoonotic infections from ruminants
• aerosol transmission; v. infectious; long-lived in environment
• grows in aveolar monos/ PMNs; survives endolysosomal fusion
• Q fever: pneumo + hepatitis
• Dx: immunohistochemistry
• Tx: tetracyclines or fluoroquinolones

Question 24

mycoplasma

Answer 24

• lack cell wall; CH in cell membrane
• smallest free-living organism; fried-egg shape colonies (except with pneumonia)
• reside on mucosal surface on inside airspace of lungs→ CARDS exotoxin-induced ciliostatis (dry cough), local inflammation and tissue destruction→ MCC walking pneumonia
• persistance through slow growth and intracellular hiding
• Abs against mycoplasma x-react with RBCs (cold agglutinins)→ anemia
• chest radiography often looks worse than patient
• Tx: tetracyclines or macrolides
  *

Question 25

coronavirus

Answer 25

* +ssRNA; 2nd MCC of cold * transmission by respiratory droplets * rare new strains cause lethal respiratory disease→ SARS, MERS

Question 26

orthomyxovirus

Answer 26

* segmented (-)ssRNA; influenza virus * envelop has 2 glycoproteins (hemagglutinin and neuraminidase) used to serotype * transmission through respiratory droplets and direct contact * Tx: tamiflu and relenza (neuraminidase inhibitors; must give early) * Flu vaccine: inactivated vaccine * FluMist: attenuated vaccine (not for babies or elderly)

Question 27

paramyxovirus

Answer 27

* measles virus * nonsegmented (-)ssRNA (little genetic variation) * croup: peak incidence in winter; starts like cold→ infants develop distinctive barking cough * Tx: at home with humidifers;

Question 28

adenovirus

Answer 28

* 100 serotypes, 47 infect humans→ pharyngoconjunctival fever * transmitted by aerosol, close contact, fecal-oral, ophthalmologic instruments * infects mucoepithelia cells * **virus persists in lymphoid tissue;** Ab essential for recovery

Question 29

hemophilus

Answer 29

* **gram-,** pleomorphic, coccobaccilus; respiratory droplets * **Hib: encapslated; more pathogenic**, covered by **vaccination** * URI→ bacteremia→ **_meningitis_,** cellulitis, **epiglottitis (cherry-red),** septic arthritis * **NTHi: unencapsulated** (still have IgA protease, pili, adhesins); less pathogenic, **no vaccination** * neonatal and postpartum sepsis, **CF pneumonia,** systemic complications after untreated local mucosal infections * culture on chocolate agar with factors X and V * Tx: amoxicillin

Question 30

b. pertussis

Answer 30

* **short, gram- rod; v. contagious;** incidence increasing due to inadequate vaccine coverage * dTaP: acellular vaccine, shorter-lived protection * dTP: whole killed pertussis * **filamentous hemagglutinin attaches to ciliated epithelial cells; exotoxin→ ciliary stasis and cell death→ whooping cough** (3 mo even with Rx) * dangerous with underlying conditions * **pronounced leukocytosis** * Tx: macrolides prevent progression and transmission but do not heal respiratory lining