Capnocytophaga canimorsus Mycotic Aortic Aneurysm After a Dog Bite

Abstract

Introduction: Mycotic aortic aneurysm is defined as dilatation of the aortic wall due to infection caused by a variety of microorganisms and is associated with high mortality rates. This case report describes a patient with a rapid growing mycotic infrarenal aneurysm caused by Capnocytophaga canimorsus following a dog bite.

Report: A 61 year old male professional dog handler presented with a history of progressive abdominal pain and constitutional symptoms. He had been bitten by a Pit Bull Terrier dog that was attacking a young girl three weeks prior to the onset of complaints. Investigations revealed a mycotic infrarenal aortic aneurysm that grew 0.5 cm in only three days. Open surgical repair consisting of an infrarenal aorto-aortic bypass with a 21 mm × 15 cm bovine bioprosthesis was performed successfully. All cultures and biopsies were negative and the subsequent 16S-23S rRNA intergenic spacer region based polymerase chain reaction (IS-pro) technique revealed C. canimorsus, a Gram negative bacterial pathogen that lives as a commensal in the gingival flora of dogs and cats that can cause a variety of severe infections, as the causative agent. Identification made it possible to treat the patient with eight weeks of intravenous followed by four weeks of oral antibiotics. At the last follow up over a year after surgery, the patient was symptom free, without infection and on ultrasound examination there were no signs of complications or aneurysm formation.

Discussion: This case highlights C. canimorsus as a rare cause of a rapid growing mycotic aortic aneurysm following a dog bite. 16S-23S rRNA profiling (IS-pro) led to the identification of the bacterial pathogen. The use of biological grafts should be considered in the management of mycotic aortic aneurysms.

Keywords: Biological graft; IS-pro; Mycotic aortic aneurysm; Open repair.

Figure 1

Computed tomography (CT) in axial (A) and coronal (B) view on admission demonstrating a 4.5 cm aortic aneurysm with inflammation of fatty tissue and fluid surrounding the aorta. ¹⁸F-fludeoxyglucose (FDG) positron emission tomography/low dose (ld) CT scan in axial (C) and coronal (D) view demonstrating significant heterogeneous FDG uptake of the aortic wall and an increase in diameter of the aortic aneurysm from 4.5 to 5.0 cm. FDG uptake was observed in retroperitoneal lymph nodes most likely reactive to the infected arterial wall. The spleen and bone marrow also showed weak uptake suggestive of an active infection. Physiological FDG uptake was seen in the brain and myocardium with signs of renal tracer excretion.

Figure 2

Intra-operative image of the bioprosthesis before (A) and after placement with the surrounding infected aortic wall (B).