Case Report Unilateral orchitis and epididymitis caused by Corynebacterium pseudotuberculosis in a stallion M. GONZALEZ*, A. TIBARY , D. C. SELLON AND J. DANIELS Washington State University, Department of Veterinary Clinical Sciences, PO Box 647060, Pullman, Washington 99164-7060, USA. Keywords: horse; testis; spermatic cord; 180° torsion; pigeon fever 30 EQUINE VETERINARY EDUCATION Equine vet. Educ. (2008) 20 (1) 30-36 doi: 10.2746/095777307X216358 Introduction In stallions, enlargement of the testis can be due to orchitis, vascular or lymphatic stasis within the testis, testicular haematoma, or testicular neoplasia (Turner 1998). Orchitis, or inflammation of the testicular parenchyma, is a relatively uncommon lesion in domesticated animals, with the exception of brucellosis in ruminants in endemic areas (Foster et al. 1996). Orchitis may be the result of infection extending from a wound, haematogenous spread of organisms, trauma, or extension of infection from the accessory sex glands (Kasaback et al. 1999). The affected testis is typically enlarged, hot, and painful. Systemic signs such as fever, leucocytosis and hyperfibrinogenaemia may also be present (Turner 1998). In stallions, bacterial orchitis is a rare condition with only a few cases reported in the veterinary literature (Belknap et al. 1988; Mohammad et al. 1989; Kasaback et al. 1999). The most common isolates in cases of orchitis and periorchitis in stallions are Streptococcus equi ssp. zooepidemicus, Actinobacillus equuli, Pseudomonas mallei, Salmonella abortus equi and Escherichia coli (Belknap et al. 1988; Mohammad et al. 1989; Kasaback et al. 1999). Corynebacterium pseudotuberculosis infection in horses may manifest in 3 different forms: ulcerative lymphangitis and external and internal abscesses (Aleman and Spier 2002). Development of internal infection is characterised by the formation of abscess(es) in several internal organs, most commonly liver, lungs, kidneys and spleen (Vaughan et al. 2004; Pratt et al. 2005). Whilst Corynebacterium pseudotuberculosis has been identified as a causative agent of epididymitis-orchitis in small ruminants (Selmo et al. 2004), that has not been the case in stallions. This report describes a case of unilateral bacterial orchitis in a stallion caused by Corynebacterium pseudotuberculosis. Case details History An 11-year-old Tennessee Walking Horse stallion was evaluated for the first time at the Veterinary Teaching Hospital (VTH), Washington State University, Pullman, on 24th March 2003, with a history of fever, lethargy and decreased appetite of 10 days’ duration. The stallion had lived in Southern Idaho his entire life and was used for breeding purposes. He was relocated to California from October 2000 to September 2001 on premises where several horses were reportedly affected by Corynebacterium pseudotuberculosis. On returning to Idaho, the horse developed an abscess in front of his chest that was successfully drained and treated by the owner with daily lavage. No other clinical signs were present and the abscess completely resolved. The stallion was regularly vaccinated and dewormed. On 18th March 2003, the horse became febrile (39.4°C), listless and anorectic. The stallion had also been grinding his teeth and stretching out as if to urinate. Repeated haematology (see Table 1) performed by the referring veterinarian showed mature neutrophilia, anaemia, elevations of liver enzymes and hyperproteinaemia characterised by mild hypoalbuminaemia and marked hyperglobulinaemia. The horse was treated with procaine penicillin (20,000 iu/kg bwt i.m. q. 12 h) from 18th–24th March and a single dose of gentamicin on 18th March. The stallion’s temperature returned to normal and his appetite improved but due to the persistence of his laboratory abnormalities, the stallion was referred to the VTH on 26th March for further evaluation. First hospitalisation Physical examination findings Upon presentation, the horse was bright and alert. He weighed 439 kg and his body condition score was estimated *Author to whom correspondence should be addressed.