Capnocytophaga canimorsus
- Bacterium
Gram-negative
Thin wall with an outer membrane: stains pink.- Exam priority: medium
A bacterium from the mouths of dogs and cats; after a bite it can cause rapid, severe sepsis, mostly in people without a spleen.
Also called: dog-bite sepsis bacterium
Quick facts
- Type
- Bacterium · Other clinically important bacteria
- Gram / shape
- Gram-negative · Thin
- Spread
- Dog bite · Not spread from person to person
- Causes
- Fulminant sepsis with septic shock · Meningitis
- Treatment
- A beta-lactam with a beta-lactamase inhibitor
At a glance
- Gram
- Gram-negative
- Shape
- Thin, long, spindle-shaped rods
- Oxygen
- Capnophilic facultative anaerobe (needs 5–10% CO2)
- Family
- Flavobacteriaceae
- Size
- Slow-growing; colonies appear after several days
Morphology
- Thin, tapered Gram-negative rods that can form filaments
- No flagella; moves on surfaces by gliding
- Grows slowly and only with added CO2
- May be seen inside neutrophils on a peripheral blood smear in fulminant sepsis
Transmission
- Dog bite, by far the most common route
- Scratches or animal saliva on broken skin; cats less often
- Not spread from person to person
Reservoir: Mouths of healthy dogs and cats
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- Resists complement killing and phagocytosis
- Its lipopolysaccharide triggers little innate alarm, so bacteria multiply silently at first
- Without a spleen the blood cannot clear it, leading to overwhelming bacteraemia and disseminated intravascular coagulation
Diseases it causes
- Fulminant sepsis with septic shock, purpura and disseminated intravascular coagulation Sepsis and septic shock →
- Meningitis Bacterial meningitis →
- Infective endocarditis Infective endocarditis →
- Local infection of the bite wound Mammalian bites (dog, cat, human) →
Clinical picture
- Fever, vomiting, diarrhoea, headache or confusion within days to two weeks after a bite
- Petechiae that progress to purpura fulminans and gangrene of fingers and toes
- Acute kidney injury and shock; the bite itself may look trivial
- Highest risk: asplenia, alcohol use disorder, cancer and immunosuppressive drugs
Diagnosis
- Tell the laboratory about the dog bite and the asplenia
- Blood cultures may take days to a week to become positive
- MALDI-TOF mass spectrometry or 16S rRNA sequencing identifies the isolate
- Broad-range PCR of blood or cerebrospinal fluid when cultures stay negative
Treatment
A beta-lactam with a beta-lactamase inhibitor (ampicillin-sulbactam, amoxicillin-clavulanic acid) or a carbapenem, with third-generation cephalosporins as another option, plus intensive sepsis care. Some strains make beta-lactamase, so penicillin alone is not reliable.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Avoid bites, especially people without a spleen or with weakened immunity
- Wash any bite promptly with soap and water and seek care the same day
- Antibiotic prophylaxis with a beta-lactam/beta-lactamase inhibitor after a dog bite in asplenic people
Test yourself
Think of the answer, then tap the question to see it.
Which underlying condition most strongly predisposes to fulminant Capnocytophaga canimorsus sepsis?
Asplenia (surgical or functional); alcohol use disorder and immunosuppression also raise the risk.
Why may blood cultures be negative at first in Capnocytophaga sepsis?
The organism grows slowly and needs CO2; cultures can take days to a week to turn positive.
Which antibiotic classes are used for Capnocytophaga canimorsus infection?
Beta-lactam/beta-lactamase inhibitor combinations or carbapenems; third-generation cephalosporins are an option.
What skin sign suggests disseminated intravascular coagulation in this infection?
Purpura fulminans, which can progress to gangrene of the fingers and toes.
Connections
← Back to the group: Other clinically important bacteria
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: About Capnocytophaga | Capnocytophaga | CDC (CDC, 2024); The Great pretender: the first case of septic shock due to Capnocytophaga canimorsus in Sardinia. A Case report and review of the literature (Journal of Public Health Research, 2022).
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Representative model, for educational purposes only.