EQUINE VETERINARY EDUCATION / AE / FEBRUARY 2018


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Clinical findings


On presentation, the mare had normal vital parameters, a body condition score of 7/9 (ideal 5/9), and a mild, bilateral serous nasal discharge. Rectal palpation revealed a viable fetus and mild gas distention of the caecum with normal faeces in the rectum. No net reflux was found on nasogastric intubation. Oral examination was normal.


Diagnosis


Complete blood cell count was within normal limits; however, hyperfibrinogenaemia was evident (21.5 lmol/L, reference range 4.4–11.76 lmol/L). Serum biochemistry showed mild hyponatraemia (125 mmol/L, reference range 126–146 mmol/ L). Brief transabdominal ultrasound confirmed a viable fetus with a heart rate of 114 beats/min while combined thickness of the uterine–placental unit (CTUP) measured normal for the gestational stage (7–8 mm) with no specific abnormalities noted. Empirical treatment included flunixin meglumine (Banamine1 1.1 mg/kg bwt, i.v., once), electrolyte water and mineral oil administered via nasogastric intubation, and feed restriction. The mare remained comfortable, continued to pass normal faeces and the hyponatraemia resolved the next day without further treatment; however, a purulent nasal discharge from the right nostril was noted. Physical examination remained otherwise normal with no signs of submandibular lymphadenopathy, while percussion of the paranasal sinuses and rebreathing examination were normal. Upper airway endoscopy revealed empyema in the medial compartment of the right guttural pouch with an apparently intact, mildly enlarged, retropharyngeal lymph node. In the left guttural pouch, a moderate amount of clear mucus was evident with no signs of retropharyngeal lymphadenopathy. A sample of the purulent exudate was collected for aerobic culture and sensitivity and S. equi ssp. equi PCR testing2.


Transthoracic and transabdominal ultrasound examination findings were within normal limits and did not show evidence of disseminated infection.


Treatment


Primary differentials for guttural pouch empyema included rupture of an abscessed retropharyngeal lymph node secondary to infection caused by S. equi ssp. equi, S. equi ssp. zooepidemicus, or another aetiological agent. The guttural pouches were subsequently treated with serial lavages using lactated Ringer’s solution (1 L once a day for 3 days) followed by infusion of potassium penicillin (5 million iu) into the right guttural pouch. Ceftiofur (Naxcel3 2.2 mg/kg bwt, i.v. q. 12 h), flunixin meglumine (Banamine1 0.5 mg/kg bwt, i.v., q. 24 h) and an oral probiotic (Equiotic4) were also administered. Due to risk of placentitis secondary to ongoing guttural pouch infection, the mare was maintained on oral altrenogest (ReguMate5 0.044 mg/ kg bwt, q. 12 h). Pending culture results, the mare was isolated from other horses. No further signs of colic were noted as both hay and grain were reintroduced. Four days later, nasal discharge had resolved and all other physical examination parameters remained normal. The mare was discharged from the clinic to continue treatment with ceftiofur crystalline free acid (Excede3 6.6 mg/kg bwt i.m., q. 4 days) and oral altrenogest at the farm.


Streptococcus equi ssp. equi PCR testing returned


negative and aerobic culture of the guttural pouch exudate yielded growth of C. pseudotuberculosis. Subsequently, a SHI titre6 was submitted and returned markedly increased, indicating C. pseudotuberculosis infection (1024) (Aleman et al. 1996). Based on culture and sensitivity results, antimicrobial therapy was changed from ceftiofur crystalline free acid to trimethoprim–sulfamethoxazole (TMS-SMZ7 20 mg/kg bwt, per os, q.12 h) and rifampicin8 (10 mg/kg bwt per os, q. 12 h). One week later, physical examination, fetal heart rate and CTUP measurements remained normal. Hyperfibrinogenaemia resolved, while the mare’s total white blood cell count and blood chemistry remained normal. Repeat upper airway endoscopy revealed pinpoint, white plaques on the walls of both guttural pouches and persistent, mild retropharyngeal lymphadenopathy in the right pouch. Repeat cultures from both guttural pouches were submitted for aerobic culture and yielded no growth9, however due to the presence of the plaques, both pouches were infused with potassium penicillin as previously described. After 6 weeks of oral TMS-SMZ treatment, endoscopic examination of the guttural pouches showed no signs of infection or lymphadenopathy and cultures collected via endoscopy remained negative. The mare continued to show no clinical signs of placentitis but altrenogest therapy was continued empirically until Day 330 of gestation, at which point this treatment was gradually tapered by 0.004 mg/kg bwt every day and discontinued 7 days later.


Outcome


The mare delivered a filly at Day 344 of gestation with a normal parturition aside from a retained placenta of 10 h duration. Routine treatment for placental retention included oxytocin10 administration (0.04 USP units/kg bwt, i.m. q. 6 h), uterine lavage (5 L lactated Ringer’s solution), systemic antimicrobial therapy (procaine penicillin G, Penject7 22,000 iu/kg bwt, i.m. q. 12 h and gentamicin, Gentafuse7 6.6 mg/kg bwt, i.v. q. 24 h), and flunixin meglumine (0.5 mg/ kg bwt, i.v., q. 12 h). The placenta appeared normal and intact once passed but the mare developed transient, mild


pyrexia for the next 24 h (38.5°C). Systemic antibiotics and flunixin meglumine were continued for 48 h followed by a 7-day course of TMS-SMZ (as previously prescribed). The mare was also treated once with intrauterine antibiotic infusion (gentamicin 6.6 mg/kg bwt buffered with equal volume [20 mL] of 8.4% sodium bicarbonate i.u.). The foal was apparently healthy and passive transfer was verified (immunoglobulin G > 8 g/L2). Blood samples collected at this time were submitted for aerobic and anaerobic culture,


which yielded no growth. One year later, both the mare and filly were reportedly healthy.


Discussion The case reported here represents a unique presentation of C. pseudotuberculosis infection manifested as guttural pouch empyema in a pregnant mare from the south-eastern USA. In a retrospective study classifying 538 cases of C. pseudotuberculosis infection in horses, only two cases of guttural pouch infection were identified and both were classified as external abscesses (Aleman et al. 1996). Although undetermined in this mare, guttural pouch infection


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