Plague etc

Question 0

Plague epidemiology

Answer 0

Bubonic: animal -> flea -> human
- mammal (rodent) -> ingested by flea -> multiplies -> obstructs foregut -> regurgitation -> lymphadenitis
- incidental flea -> human
Pneumonic: human -> human
- bubonic -> septicemia -> pneumonia -> droplet transmission

Urban: epidemic among rats and fleas (Xenopsylla cheopis)
-> flea need new hosts -> bubonic -> pneumonic
Rural: endemic or epidemic among rats
-> flea bite, hand contact, pets
- India, South America, South Africa, southern Russia, US (10/yr)

Question 1

Plague bacteriology

Answer 1

Yersinia pestis
- Enterobactericiae (also Y pseudotuberculosis, enterocolitica)
Large bacillus/pleiomorphic coccobacillary
Gram negative
“Bipolar” Giemsa stain (“safety pin”)
Facultative aerobe - oxidase (-), catalase +
- fermentation: glucose +, lactose (-)
Non-motile

Question 2

Plague pathogenesis

Answer 2

Mostly extracellular
- F1/capsule = anti-phagocytic (at 37C but not flea temp)
- V, W antigens -> survive in macrophages
Toxins - LPS, exotoxin

Bubonic -2-6d> fever, malaise, painful lymphadenopathy
Pneumonia - classical suppurative -> rapid death
Septicemia: untreated bubonic or pneumonia -> abdo pain, shock
Complications:
- DIC -> hemorrhage (“black death”)
- meningitis

Question 3

Plague clinical

Answer 3

Dx: bubo, blood, sputum -> Gram and fluorescent antibody (F1)
- or serum antibody vs F1 (4x increase)
- may have high bacteremia (visible organisms)
Tx: 10 d of tetracycline, streptomycin, chloramphenicol
- mortality 60-90% untreated, 5% if early rx (15% in US overall)
- adverse prognostics - axillary nodes, bacteremia, secondary pneumonia

Vaccine (inactivated) effective in Vietnam War

Question 4

Tularemia bacteriology

Answer 4

Francisella tularensis
Gram negative pleiomorphic
 - small, unencapsulated
Aerobic, fastidious/slow (Cysteine+glu+blood or thioglycollate)
 - cold tolerant (ie water for 90 days)

Question 5

Tularemia transmission

Answer 5

Low infectious dose (5-10 organisms)
Widespread zoonosis - mammals, insects, water, soil

Mammals - handling (live or dead), ingestion (meat, water), bite
- rabbits, muskrats, etc
-> winter in eastern US
Insects - deer flies, ticks -> summer in western US
Aerosol - shaking dog, mowing lawn, lab

Tick control, gloves
Attenuated vaccine available for trappers, lab workers

Question 6

Tularemia pathogenesis

Answer 6

Largely intracellular - survives in macrophages
Skin (wound, bite), inhalation ->
-> local lymph -> bacteremia -> granulomas in spleen, liver
Endotoxin

Abrupt onset of sx - fever, malaise - 3-5d incubation
Ulceroglandular - common - skin ulcers, painful lymphadenopathy
Typhoidal = bacteremia
Pneumonia (10-15%) - rarely primary from aerosol

Question 7

Tularemia clinical

Answer 7

Difficult and dangerous to culture!

• fluorescent antibody stains
• serum titers - 4x increase - cross-reacts with brucella

Streptomycin x 7-10 d = cidal

• alternative tetracycline x14d, chloramphenicol, cipro
• post-exposure prophylaxis available (doxycycline, cipro)
• mortality low with tx (1%)
• relapses due to intracellular persistence

Question 8

Brucellosis bacteriology and transmission

Answer 8

Gram negative rod (pleiomorphic)
Fastidious, slow - requires 10% CO2

Common zoonosis in developing -> infective abortions

• B abortis - cattle -> milk, cheese, slaughterhouse
• B suis - pigs -> contact, aerosol, slaughterhouse
• B melitensis - goats, sheep -> dairy
• B canis -> urine

Prevention:

• pasteurization
• vaccinate calves
• herd testing - individual or pooled milk
• occupational protections (mask, gloves)

Question 9

Brucellosis pathogenesis

Answer 9

Ingestion (unpasteurized diary) or contact (slaughterhouse)

• > monocytes -> intracellular
• > granulomas in spleen, liver, kidney, marrow

“Malta” fever, Mediterranean, undulant fever

• difficult to recognize - resembles cold
• systemic - fever, myalgias, arthralgias
• intracellular -> prolonged sx, relapses
• > osteomyelitis
• > endocarditis (culture (-))

Question 10

Brucellosis clinical

Answer 10

Difficult to recognize - systemic, non-specific, prolonged
Occupational history
Blood culture - prolonged bacteremia, incubation 21 d
Serum antibody - cross-reaction from typhoid, tularemia, cholera vaccine, skin test
Bone marrow biopsy

Doxycycline + rifampin x6 wks

• 1-2% mortality
• 25% relapse