STEPTRACKERMICROBIOLOGY + PUBLIC HEALTH | ZOONOSES | HIGH-YIELD REVIEW

Zoonotic Bacteria

Infections caught from animals — the exposure history is the diagnosis. Learn each organism by its animal, its route and its signature finding.

FOCUS ON
Exposure → organism: cat scratch → Bartonella henselae (lymphadenitis; bacillary angiomatosis in AIDS); cat/dog bite → Pasteurella multocida (cellulitis within 24 h, amoxicillin-clavulanate); unpasteurized dairy → Brucella (undulant fever); rabbits, ticks, deer flies → Francisella tularensis (ulceroglandular tularemia); fleas from rodents → Yersinia pestis (bubonic, pneumonic plague); tick → Borrelia, Rickettsia, Ehrlichia, Anaplasma; animal urine in water → Leptospira; livestock aerosols → Coxiella. Many are facultative intracellular — doxycycline or aminoglycosides (streptomycin, gentamicin).
ORGANISM
ANIMAL · ROUTE
DISEASE
CLUE · TREATMENT
Bartonella henselae
Cat scratch or bite (kittens, fleas)
Cat scratch disease: papule then tender regional lymphadenopathy, stellate granulomas
Self-limited or azithromycin
Bacillary angiomatosis
B henselae or B quintana in AIDS (CD4 < 100)
Red-purple vascular papules (mimic Kaposi sarcoma); neutrophilic infiltrate
Kaposi = lymphocytic; biopsy · doxycycline or erythromycin
Bartonella quintana
Body lice (homelessness)
Trench fever, culture-negative endocarditis
—
Pasteurella multocida
Cat or dog bite/scratch
Rapid cellulitis (< 24 h), osteomyelitis, septic arthritis
Amoxicillin-clavulanate prophylaxis for bites
Capnocytophaga canimorsus
Dog bite
Fulminant sepsis, DIC in asplenic or alcoholic patients
—
Brucella
Unpasteurized milk/cheese, livestock work
Undulant fever, night sweats, arthralgia, sacroiliitis, hepatosplenomegaly, granulomas
Doxycycline + rifampin
Francisella tularensis
Rabbits, ticks, deer flies; hunters skinning game
Ulcer at entry site + painful regional nodes; pneumonic form (bioterrorism)
Very low infectious dose · streptomycin or gentamicin
Yersinia pestis
Flea bites from rodents (prairie dogs, US Southwest)
Bubonic: painful swollen nodes (buboes); septicemic; pneumonic (person-to-person)
Bipolar "safety pin" staining · streptomycin or gentamicin
Leptospira interrogans
Water contaminated with animal (rat) urine; surfers, flooding, tropics
Fever, myalgia (calves), conjunctival suffusion; severe: Weil disease (jaundice, AKI, hemorrhage)
See 4.08 · doxycycline, penicillin
Coxiella burnetii
Inhaled spores from cattle/sheep birth products — no tick needed
Q fever: pneumonia, hepatitis; chronic → culture-negative endocarditis
See 3.03 · doxycycline
Chlamydophila psittaci
Parrots, other birds
Atypical pneumonia, splenomegaly
Doxycycline
Salmonella · Campylobacter
Reptiles, poultry · puppies
Gastroenteritis
See 4.05

Mechanism — why doxycycline works for zoonoses

Facultative/obligate intracellularBrucella, Francisella, Rickettsia, Coxiella
→
Survive in macrophagesGranulomas
→
Need drugs that enter cells
→
Doxycycline, rifampin, macrolides

Animal → organism

ANIMAL
ORGANISM
DISEASE
Cat
Bartonella, Pasteurella, Toxoplasma
Lymphadenitis, cellulitis
Dog
Pasteurella, Capnocytophaga
Cellulitis, sepsis
Rabbit
Francisella
Tularemia
Rodent fleas
Y pestis
Plague
Cattle, sheep, goats
Brucella, Coxiella
Undulant fever, Q fever
Birds
C psittaci, Histoplasma
Pneumonia
Rat urine
Leptospira
Weil disease

How it's tested

COMMON CONFUSIONBacillary angiomatosis (Bartonella; neutrophils; treat with antibiotics) vs Kaposi sarcoma (HHV-8; lymphocytes, spindle cells).
THE TRAPQ fever comes from inhaled spores, not ticks — the one rickettsial-like infection with no rash and no vector.
YOUR APPROACHAsk the animal and exposure → organism → intracellular? → doxycycline or aminoglycoside.

If you see… think…

Child with tender axillary node after a kitten scratch → Bartonella henselae
AIDS patient with red vascular papules, neutrophils on biopsy → bacillary angiomatosis
Cellulitis within a day of a cat bite → Pasteurella multocida
Asplenic patient septic after a dog bite → Capnocytophaga
Relapsing fevers after unpasteurized goat cheese → Brucella
Hunter with hand ulcer and axillary nodes after skinning a rabbit → tularemia
Painful bubo in New Mexico after prairie dog contact → Y pestis
Jaundice, AKI, conjunctival suffusion after flood water → Leptospira (Weil)
Farmer with pneumonia after lambing season → Coxiella (Q fever)
Pet bird owner with atypical pneumonia → C psittaci