A 60-year-old woman presented in septic shock two days after being bitten on the calf by a dog. Twenty-four years previously she had required a splenectomy for autoimmune thrombocytopenic purpura with the platelet count remaining normal thereafter. On clinical examination, the patient had a mottled rash on her left leg which, within 24 hours, had developed into extensive purpura fulminans involving the extremities and the buttocks. She also developed disseminated intravascular coagulation (DIC) and multiorgan failure. 1

The full blood count on admission showed a white cell count of 11.3 × 109/l, neutrophils 8.3 × 109/l, hemoglobin concentration 11.3 g/dl and platelet count 38 × 109/l. The blood film showed features of hyposplenism and in addition the presence of bacilli within neutrophils (image), supporting a diagnosis of Capnocytophaga canimorsus septicaemia. This was subsequently confirmed by blood culture. Histology of the excised dog bite site showed necrotic skin with thrombi in small vessels in the underlying subcutaneous tissue. Despite early diagnosis, broad spectrum antibiotics and intensive support the patient developed gangrene of one hand and the soles of her feet and died twelve days after presentation.

Capnocytophaga canimorsus, formerly known as dysgonic fermenter 2 (DF-2), is a commensal bacterium of dog and cat saliva. It can be transmitted to humans by a bite, a scratch or mere licking. Hyposplenic patients are particularly at risk of septicaemia, DIC and death and should be warned about the risks of close contact with cats and dogs. Urgent examination of a blood film is indicated in such patients presenting with a febrile illness after dog-bite, although even rapid diagnosis and urgent treatment may not prevent death.