Beyond the fear of tetanus

Abstract

While quoted as 'man's best friend', a commensal found commonly in the oral cavity of dogs can cause fulminant sepsis in humans. Although Clostridium tetani is prominent, few may know about Capnocytophaga carnimorsus. We attended a patient with multi-organ failure, purpuric rash and limb ischaemia resulting in above knee amputations. Description A previously well 62-year-old female presented to the ED shocked with significant metabolic acidosis (pH 6.9 and lactate 20). Of note was rapidly spreading purpura, leading initial suspicion to meningococcal septicaemia. She had crystalloid resuscitation, peripheral vasopressors and central access for noradrenaline. Following ketamine induction she was intubated and transferred to ITU for multi-organ support (included RRT, high inotropic requirements and management of DIC). Two days prior she sustained an apparently trivial dog bite to her finger while separating her dog fighting the pet rabbit. Discussion with haematologists raised the possibility of C. canimorsus. Knowing the organism is slow growing on standard agar but visible as phagocytised rods in neutrophils and macrophages, the haematologist reviewed the peripheral blood film, which confirmed this suspicion. Microbiology colleagues isolated and identified the organism. Fortuitously, she was on appropriate antibiotics from the outset, but had presented late to the ED. Despite improved physiological parameters, she developed widespread necrosis requiring bilateral above knee amputations. After a turbulent period on ITU, including cardiac arrests, she rehabilitated well and made good physical and cognitive recovery; however, she has rehomed the dog. Discussion C. canimorsus is a fastidious, capnophilic gram negative rod, described in 1976 [1]. While previously known to cause sepsis and endocarditis in humans, the overwhelming majority of patients were immunosuppressed, including asplenic and alcoholic patients. A quarter of UK households own a dog [2]. There are over 7000 dog bites per year in the UK and PCR samples show presence of C. canimorsus in up to 75% of dogs and 57% of cats [3]. Thus, exposure to C. canimorsus is potentially grossly underestimated. Although tetanus is commonly thought of in the context of dog bites, C. canimorsus should not be overlooked. Patients should be advised to have low thresholds seeking medical advice regardless of tetanus status. C. canimorsus should always be considered in the differential diagnosis of any septic patient with a recent animal bite.