Capnocytophaga canimorsus
💉 Empirical antibiotic therapy should always be considered for dog bites in the elderly, deep penetrating bites, and bites to the hand.
⚠️ Capnocytophaga species are emerging zoonotic pathogens that can cause fulminant systemic infections, particularly in immunocompromised or asplenic individuals.
ℹ️ About
- 🐶🐱 Capnocytophaga canimorsus – commensal bacterium in the gingival flora of cats and dogs
- 📅 First described in 1976
🧬 Characteristics
- 🦠 Fastidious, slow-growing, Gram-negative bacillus
- 🧪 Gram-negative organisms have a lipid-rich outer membrane → contributes to antibiotic resistance (e.g. penicillin)
- 🌡️ Difficult to culture; often overlooked unless clinical suspicion is high
🩺 Clinical Manifestations
- 🌡️ Sepsis, PUO (pyrexia of unknown origin)
- 🧠 Meningitis, pneumonia
- 🩹 Cellulitis, phlebitis
- ❤️ Endocarditis, DIC, septic shock
- 💧 Urosepsis, fulminant bacteraemia (especially in asplenic patients)
📍 Source of Infection
- 🐶 Normal oral flora in dogs; 🐱 also present in cats
- 🚨 Transmission: bites, scratches, licking of wounds, or even close contact
- 💡 Important clue: history of recent animal exposure
⚠️ Risk Factors
- 🪓 Splenectomy or functional asplenia (highest risk of overwhelming sepsis)
- 🩸 Hyposplenism (e.g. sickle cell disease)
- 🍺 Alcoholism (immune dysfunction)
- 🧓 Elderly, immunocompromised, chronic liver disease
🦠 Pathogenicity
- 📉 Low virulence in healthy individuals; often asymptomatic
- ⚡ Can cause severe, life-threatening infection in those with pre-existing conditions
- 🔬 Virulence factors: catalase & sialidase production, gliding motility, cytotoxin release
- 🛡️ Unique lipopolysaccharide → resistance to complement-mediated killing
🔎 Investigations
- 🧾 Clinical history: exposure to dogs or cats
- 🧪 Blood culture: oxidase- and catalase-positive, fusiform Gram-negative rods (slow growing)
- 🧬 PCR or molecular techniques: useful when culture is negative
- ⚠️ Always check splenic function in severe/recurrent infections
💊 Management
- 💉 Penicillin is traditionally the drug of choice
- 💊 Alternatives: third-generation cephalosporins (e.g. ceftriaxone) or beta-lactam/beta-lactamase inhibitor combinations
- 💊 Co-amoxiclav is standard first-line empirical therapy for dog bites (covers Pasteurella, Capnocytophaga, anaerobes)
- 🏥 Severe sepsis: treat with IV broad-spectrum antibiotics until sensitivities confirmed
💊 Case Reports
- 🐶 Case 1 – Age 62 (Asplenic Patient with Sepsis): Man with previous splenectomy for trauma presented with fever, rigors, and hypotension two days after a dog bite to his hand. Rapid progression to septic shock with DIC and purpura.
Investigations: Blood cultures grew Capnocytophaga canimorsus.
Management: IV benzylpenicillin and ceftriaxone; ICU admission for vasopressor support.
Teaching point: C. canimorsus is a gram-negative rod from dog and cat oral flora that causes overwhelming sepsis in asplenic or immunocompromised hosts — prompt empiric antibiotics are lifesaving.
- 🩸 Case 2 – Age 55 (Alcohol Misuse): Chronic alcoholic man presented with fever, myalgia, and confusion 72 hours after being licked over an open wound by his pet dog. Initial WCC low with rising bilirubin and CRP.
Investigations: Blood culture positive for Capnocytophaga canimorsus.
Management: Treated with IV co-amoxiclav for 14 days with full recovery.
Teaching point: Even minor dog contact can transmit C. canimorsus in individuals with hepatic dysfunction, alcohol excess, or immune suppression — meticulous wound care and early antibiotics are essential.
