EQUINE VETERINARY EDUCATION / AE / OCTOBER 2014


507


Case Report


Survival of an adult Quarter Horse gelding following bacterial meningitis caused by Escherichia coli


K. L. Hepworth*, D. M. Wong, B. A. Sponseller, C. J. Alcott, B. T. Sponseller, G. Ben-Shlomo and R. D. Whitley


Lloyd Veterinary Medical Center, College of Veterinary Medicine, Iowa State University, Ames, Iowa, USA. *Corresponding author email: hepworth@iastate.edu Keywords: horse; haematogenous; nasal abscess; post traumatic blindness; skull trauma


Summary Bacterial meningitis in the mature horse is a rare and typically fatal condition. This report describes a 7-year-old Quarter Horse gelding that initially presented following suspected trauma to the left eye but subsequently developed bacterial meningitis, and a nasal and palpebral abscess, all of which cultured the same isolate of Escherichia coli. The entry site of infection in bacterial meningitis is often related to a breach in the calvarium and extension of bacteria residing in the paranasal sinuses. This case is unique as there were multiple pathways through which bacteria may have entered the central nervous system including haematogenous spread from a nasal abscess, local extension of periocular infection or an undetected skull fracture. Aside frompersistent blindness in the left eye, the horse made a full recovery.


Introduction


Bacterial meningitis in the mature horse is a rare and typically fatal condition (Smith et al. 2004; Mitchell et al. 2006; Pusterla et al. 2007; Toth et al. 2012). The occurrence of bacterial meningitis in the neonatal foal is more common, as a sequela to sepsis (Viu et al. 2012). Reports of mature equids presenting with bacterial meningitis are scarce, and most die or are subjected to euthanasia due to a poor prognosis after a rapid disease course. Clinical signs of bacterial meningitis vary, reflecting widespread inflammation within the central nervous system (CNS) once infection is established. Clinical signs may wax and wane and include marked depression, head pressing, ataxia, cranial nerve deficits, muscle tremors, dysphagia, stiffness, seizures, urinary incontinence and recumbency. Pyrexia, tachycardia and tachypnoea are variable clinical findings (Timoney and McArdle 1983; Newton 1998; Smith et al. 2004; Pellegrini-Masini et al. 2005; Mitchell et al. 2006; Pusterla et al. 2007). In many cases, there is rapid deterioration of the animal’s condition. The case reported here describes a horse that developed


bacterial meningitis suspected to originate from haematogenous dissemination from a nasal abscess or extension of periocular infection.


Case history


A 7-year-old Quarter Horse gelding weighing 570 kg was referred to the Iowa State University Lloyd Veterinary Medical Center following suspected trauma to the left eye and concern for rupture of the left globe. The horse was reportedly healthy on the morning of presentation and was found later in the afternoon with marked periorbital swelling, chemosis and a


marked quantity of serous ocular discharge. The horse had no prior health issues before this event. The owners assumed he had suffered a kick from a pasture mate.


Initial clinical findings


On initial examination, the horse was quiet but alert and responsive. Mild tachycardia (50 beats/min) was present; all other vital parameters were within normal limits. The right submandibular lymph node was markedly enlarged, closed mouth percussion of the paranasal sinuses revealed dullness over the left frontal sinus, subcutaneous oedema and emphysema surrounded the left orbit, and mucopurulent nasal discharge was noted from the left naris. No abnormalities were noted over the right paranasal sinuses or in the right naris. No neurological deficits were noted, although severe swelling of the left eye precluded complete assessment. Initial ophthalmological examination was limited due to severe chemosis. A small portion of the globe was visualised, revealing a miotic pupil and digital palpation indicated normal tone of the left eye. Radiographs were taken of the periorbital area and


caudal portion of the skull including right and left oblique projections, a dorsoventral projection, and a left lateral projection. These images demonstrated no evidence of fractures or fluid in the paranasal sinuses. Initial treatment included flunixin meglumine (Prevail1 1.1 mg/kg bwt i.v. b.i.d.), dexamethasone (Dexamethasone solution1 0.09 mg/kg bwt i.v.), furosemide (Salix7 0.88 mg/kg bwt i.v. once) and topical ocular treatment of the left eye including atropine ointment (Atropine sulfate8, to effect), triple antimicrobial ointment (Neomycin Polymyxin B Bacitracin ophthalmic ointment8, left eye, t.i.d.), and hypertonic saline ointment (Muro 5%8 left eye once). Due to the high suspicion that the clinical signs were a result of trauma, no further diagnostics or clinicopathological data were performed. The following day the horse remained bright, alert,


responsive, and had a normal appetite. Physical examination excluding the left eye was within normal limits. Administration of flunixin meglumine and dexamethasone (decreased dose by 10 mg daily, discontinued after 20 mg dose) continued. Upon re-examination of the left eye, fluorescein stain uptake revealed coalescing superficial ulcers spanning the central third of the cornea. Periocular and conjunctival swelling were minimally reduced; therefore a temporary tarsorrhaphy was performed to decrease the chemosis and to keep protruding conjunctiva from becoming desiccated. Triple antimicrobial ointment and atropine ointment were instilled prior to the tarsorrhaphy then temporarily discontinued. A combination of


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