Internal abdominal abscesses caused by Streptococcus equi subspecies equi in 10 horses in California between 1989 and 2004

Streptococcus equi subspecies equi has been recognised for many years as the causative organism of strangles, an infectious and highly contagious respiratory disease of young horses. Due to the highly contagious nature of the pathogen, morbidity rates range from 30 to 100 per cent, depending on the immune status of the exposed horse population (Sweeney and others 1987a). Strangles is characterised by the sudden onset of fever and upper respiratory tract catarrh, as evidenced by mucopurulent nasal discharge. These signs are commonly followed by the formation of abscesses in the submandibular and retropharyngeal lymph nodes. After the affected lymph nodes rupture and drain spontaneously or are surgically lanced and flushed, the disease runs its course and affected horses usually recover uneventfully, leaving 75 per cent of exposed horses with a solid, enduring immunity (Hamlen and others 1994). However, a number of complications, including metastatic spread of infection or immunemediated processes, have been reported to occur in approximately 20 per cent of S equi infections and are associated with a significant increase in fatality rate (Ford and Lokai 1980, Sweeney and others 1987b, Spoormakers and others 2003). Metastatic spread of the organism to locations such as the thorax, lungs, brain, mesentery, liver, spleen and kidneys has been reported and may occur haematogenously, through lymphatic migration or via extension from a closely associated septic focus (Ford and Lokai 1980, Sweeney and others 1987b). Although internal abdominal abscesses due to S equi are mentioned in the veterinary literature, there is little reference to the clinical diagnosis and management of this condition. This short communication describes the history, clinical signs, laboratory data, results of diagnostic imaging techniques, treatment and outcome in 10 horses with internal abdominal abscesses caused by S equi. A computer search of the medical record database of horses examined at the Veterinary Medical Teaching Hospital (VMTH), University of California, between 1989 and 2004 was undertaken to identify potential candidates. Ten horses with one or more internal abdominal abscesses due to S equi were included in the study, based on clinical signs (presence of an internal abdominal mass on rectal examination), ultrasonographic findings, inflammatory peritoneal fluid, positive culture of S equi from an abdominal abscess or a high to very high titre against S equi. The data derived from the medical records included signalment, presenting complaint, duration of clinical signs, physical examination findings, laboratory results (haematology, biochemistry, peritoneal fluid cytology, culture and S equi serology), abdominal ultrasound, treatment and outcome, as well as postmortem examination findings when available. The horses ranged in age from one to 12 years (mean four years) and included four mares, four geldings and two stallions (Table 1). The mean duration of illness before admission to the VMTH was 25 days, with a range of one day to three months. Nine horses had been boarded at facilities on which an outbreak of S equi infection had occurred between three weeks and four months before presentation to the VMTH. During the reported outbreaks, these nine horses had experienced signs compatible with strangles. One horse originated from a facility with an unknown S equi status and had no previous history of respiratory disease. Historical problems reported by owners were weight loss, fever, colic, partial or complete anorexia, depression and tachypnoea. While seven horses presented with chronic signs, three horses were referred to the VMTH for acute colic. Eight horses had been treated with antimicrobials and/or anti-inflammatory drugs by a referring veterinarian or the owner before presentation. Seven horses were bright and alert at presentation, two horses were mildly depressed and one horse showed signs of severe colic (Table 1). Other commonly reported clinical findings included tachycardia (heart rate >44 bpm), tachypnoea (respiratory rate >20 breaths/minute), fever (rectal temperature >38·5°C) and low body condition score (BCS) (<5/9). Rectal examination revealed a mass caudal to the left kidney in four horses or in the caudoventral abdomen in four horses. Rectal examination was unremarkable in two horses. Results of a complete blood count and serum biochemical panel were available for all horses. The most common laboratory abnormalities detected were anaemia (packed-cell volume <30 per cent), leucocytosis (>11,600 white blood cells/μl), neutrophilia (>6800 neutrophils/μl), thrombocytosis (>225,000 platelets/μl), hyperproteinaemia (>7·7 g/dl), hyperglobulinaemia (>4·7 g/dl) and hyperfibrinogenaemia (>400 mg/dl) (Table 2). The only biochemical abnormalities were elevated creatinine concentration (>2 mg/dl) and blood urea nitrogen (>27 mg/dl) in two horses, elevated aspartate