What is the most likely cause of a flu-like illness that progresses to rapid shock, disseminated intravascular coagulation, acute kidney injury, and thrombocytopenia within 24–72 hours after a dog bite?

Capnocytophaga canimorsus Septic Shock

The most likely cause is Capnocytophaga canimorsus infection, a gram-negative bacterium from the dog's oral flora that causes fulminant septic shock with DIC, purpura fulminans, acute kidney injury, and thrombocytopenia within 24-72 hours of a dog bite, particularly in asplenic or immunocompromised patients. 1, 2, 3

Pathogen and Clinical Presentation

Capnocytophaga canimorsus is part of the normal oral microbiome of dogs and is isolated from approximately 60% of dog bite wounds alongside other pathogens including Pasteurella multocida (50%), staphylococci, and streptococci. 4 However, C. canimorsus is uniquely associated with this specific fulminant presentation:

• Rapid progression to septic shock occurs within 24-72 hours of dog bite exposure 1, 2, 3
• Purpura fulminans with diffuse petechial bleeding and central necrosis develops as part of the clinical syndrome 2, 3
• DIC with thrombocytopenia results from systemic coagulation activation and microvascular thrombosis 1, 2, 3
• Multi-organ failure including acute kidney injury, respiratory failure, and cardiovascular collapse is characteristic 1, 2, 3

High-Risk Patient Populations

The most critical risk factor is asplenia (surgical or functional), which dramatically increases susceptibility to overwhelming sepsis from encapsulated organisms and C. canimorsus. 1, 3 Other high-risk conditions include:

• Advanced liver disease or cirrhosis 4
• Immunocompromised states 5, 2
• Chronic alcohol use 2

Even immunocompetent patients can develop this syndrome, though it is less common. 1

Diagnostic Approach

Immediate Recognition

• Flu-like prodrome (fever, malaise, myalgias) rapidly progressing to shock within 24-72 hours of dog bite 1, 2
• Peripheral cyanosis and purpuric rash with petechiae and central necrosis 2, 3
• Laboratory findings: marked leukocytosis, elevated CRP and procalcitonin, thrombocytopenia, prolonged PT/PTT, elevated D-dimers, acute kidney injury 2, 3

Microbiologic Diagnosis

Critical pitfall: C. canimorsus is a slow-growing, fastidious, microaerophilic gram-negative rod that may take days to grow in standard blood cultures. 2

• Gram stain of peripheral blood smear may provide early diagnosis and should be performed immediately in suspected cases 2
• Blood cultures should be held for extended incubation (up to 7-10 days) 2
• Gene sequencing may be required for definitive identification 2

Immediate Management

Antibiotic Therapy

Start empiric broad-spectrum antibiotics immediately without waiting for culture results, as delay is associated with fatal outcomes. 2

• First-line IV therapy: Ampicillin-sulbactam 1.5-3.0 g every 6-8 hours OR piperacillin-tazobactam 3.37 g every 6-8 hours 6, 1, 2
• These regimens provide essential coverage against C. canimorsus, Pasteurella, staphylococci, streptococci, and anaerobes 6, 4

Avoid monotherapy with: first-generation cephalosporins, penicillinase-resistant penicillins, macrolides, or clindamycin due to poor activity against Pasteurella and Capnocytophaga species. 6

Septic Shock Management

Follow Surviving Sepsis Campaign guidelines for septic shock resuscitation: 5

• Aggressive fluid resuscitation with crystalloids 5
• Vasopressor support (norepinephrine first-line) for refractory hypotension 5
• Source control: surgical debridement if indicated 5

DIC Management

The presentation represents overt DIC requiring supportive care: 5

• Platelet transfusion for active bleeding or severe thrombocytopenia (typically <10,000-20,000/μL) 5
• Fresh frozen plasma to reverse coagulopathy and replace consumed anticoagulant proteins (protein C, antithrombin III) in patients with progressive purpura and prolonged PT/PTT 5
• Anticoagulation (unfractionated heparin or LMWH) may be considered in early DIC with predominant thrombotic features, but must be balanced against bleeding risk 5

Organ Support

• Renal replacement therapy for acute kidney injury 1, 3
• Mechanical ventilation for respiratory failure 2
• Stress-dose hydrocortisone (50 mg/m²/24h) if adrenal insufficiency suspected (Waterhouse-Friderichsen syndrome) 5, 3

Prognosis and Complications

Mortality remains high (up to 30-40%) despite appropriate therapy, particularly when treatment is delayed. 2, 3 Survivors may require:

• Multiple limb amputations due to symmetrical peripheral gangrene from microvascular thrombosis 5, 3
• Prolonged ICU care with multi-organ support 1, 2

Prevention

All dog bite wounds require risk stratification: 4

• High-risk wounds (hand/foot wounds, facial wounds, immunocompromised/asplenic patients) mandate prophylactic antibiotics with amoxicillin-clavulanate 875/125 mg twice daily 4
• Asplenic patients should receive immediate prophylactic antibiotics after ANY dog bite, regardless of wound severity 4, 1, 3
• Patient education for asplenic individuals about the risk of overwhelming sepsis from animal bites is essential 1, 3