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EQUINE VETERINARY EDUCATION


Equine vet. Educ. (2018) 30 (2) 76-79 doi: 10.1111/eve.12684


Case Report


Guttural pouch empyema caused by Corynebacterium pseudotuberculosis in a pregnant mare


P. DeLoache†, D. Whelchel†*, R. Beetz†, J. Carter†, A. Eichelberger‡ and N. Pusterla§ †Southern Equine Service, Aiken; ‡Clemson University Livestock Poultry Health, Columbia, South Carolina; and §UC Davis School of Veterinary Medicine Department of Medicine and Epidemiology, Davis, California, USA. *Corresponding author email: whelcheld@missouri.edu


Keywords: horse; Corynebacterium pseudotuberculosis; pigeon fever; guttural pouch empyema; internal abscess


Summary During medical management of mild colic in a 12-year-old Quarter Horse, mid-gestation mare, unilateral purulent nasal discharge from the right nostril was noted. Endoscopic examination revealed guttural pouch empyema. Culture was positive for Corynebacterium pseudotuberculosis and negative for Streptococcus equi ssp. equi. A synergistic haemolysis inhibition titre of 1024 was consistent with C. pseudotuberculosis infection. Treatment included serial lavages and local infusion of antibiotics into the guttural pouches along with a 6-week course of oral trimethoprim– sulfamethoxazole and rifampicin. Overall, no additional sites of infection were identified and the mare responded well to treatment, delivering a healthy, full-term foal. This case emphasises that C. pseudotuberculosis, although uncommon, should be considered as a differential for guttural pouch empyema.


Introduction


Corynebacterium pseudotuberculosis is a soil borne, Gram- positive, facultative anaerobic intracellular bacterium known for causing abscesses in ruminants and horses worldwide (Aleman et al. 1996). This bacterium can be further classified into two different biovars based on nitrate reducing capabilities with the nitrate reducing biovar equi causing abscesses in horses (Biberstein et al. 1971). The classic presentation in horses, known as ‘pigeon fever’ or ‘dryland distemper,’ is characterised by external abscess formation in the pectoral, axillary, ventral midline, mammary or preputial regions (Aleman et al. 1996). Internal abscesses and ulcerative lymphangitis are less common manifestations of infection (Aleman et al. 1996; Pratt et al. 2005, 2006; Nogradi et al. 2012). The disease is typically diagnosed from November to January with external abscesses preceding internal abscesses by an average of 1–2 months (Pratt et al. 2005). C. pseudotuberculosis has a worldwide distribution and is considered endemic to the western and south-western USA with 5–10% prevalence (Spier 2008). Over the past decade, the occurrence of C. pseudotuberculosis infection in horses has increased throughout the country with rising numbers of cases in the eastern USA from 2010 to 2013, including states where the disease is not considered endemic (Foley et al. 2004; Spier 2008; House 2012; Kilcoyne et al. 2014). The bacterium survives in the soil while insect vectors and regional climate changes probably play a role in disease transmission and seasonal occurrence (Spier et al. 2004; Spier 2008; Barba et al. 2015).


© 2016 EVJ Ltd External abscesses commonly present as deep


intramuscular or subcutaneous abscesses that resolve with localised drainage and supportive care (Aleman et al. 1996). In contrast, internal abscesses represent <10% of total diagnosed C. pseudotuberculosis infections, with abscesses forming in multiple organ systems including the lungs, liver, spleen and kidneys or causing conditions such as infectious pericarditis, pleuritis and meningitis (Aleman et al. 1996; Perkins et al. 2004; Pratt et al. 2005, 2006; Rand et al. 2012). This form of infection carries a guarded prognosis with mortality rates ranging from 29 to 40% (Aleman et al. 1996; Pratt et al. 2005). Clinical signs of internal infection are often nonspecific, including anorexia, lethargy, weight loss, mild colic or signs associated with respiratory disease (Pratt et al. 2005). Initial diagnosis is based on clinical pathology and diagnostic imaging, such as transabdominal ultrasound, to identify internal abscesses. Definitive diagnosis can be confirmed with culture of C. pseudotuberculosis or synergistic haemolysis inhibition (SHI) titres ≥1:512 (Knight 1978; Aleman et al. 1996; Pratt et al. 2005). While guttural pouch empyema secondary to other


pathogens is not uncommon, C. pseudotuberculosis infection in the guttural pouches appears to be a rare occurrence, with only two other cases described prior to this report (Aleman et al. 1996). Frequently, guttural pouch empyema or chondroids develop secondary to the rupture of abscessed retropharyngeal lymph nodes infected with Streptococcus equi ssp. equi or S. equi ssp. zooepidemicus. Serial lavages with sterile fluids to remove debris along with local and systemic antimicrobial therapy are necessary to resolve infection (Judy et al. 1999).


Case history


In December 2013, a 12-year-old Quarter Horse mare at 7 months’ gestation presented for mild colic. The owner noted lethargy, decreased appetite and intermittent, serous, nasal discharge from the right nostril of 48 h duration. The mare had two prior pregnancies but aborted the previous year after undergoing surgical correction of a right dorsal large colon displacement. The mare was artificially inseminated with cooled semen in May 2013 and pregnancy was confirmed at 90 days’ gestation. The mare was kept on the owner’s farm in South Carolina with two other apparently healthy horses. Nine months prior to presentation, one of these horses developed a pectoral abscess that was lanced and drained without further complication; culture results were negative for C. pseudotuberculosis.


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