Tyzzer disease (TD) is caused by Clostridium piliforme, a gram-negative and obligate intracellular bacterium. The disease occurs in multiple species. A triad of lesions, namely colitis, hepatitis, and myocarditis, is described in cases of TD in some species, such as rats and mice. We carried out a retrospective analysis of 25 equine cases with a diagnosis of TD; 24 of 25 cases occurred in foals <45 d old; the remaining foal was 90 d old. There were 12 males and 12 females; no sex information was available for one foal. The affected breeds were Quarter Horse, Thoroughbred, Arabian, Paint, and Hanoverian. Most of the cases (19 of 25) occurred in the spring. There were 9 cases of sudden death; the remaining animals had diarrhea, fever, distended abdomen, depression, weakness, non-responsiveness, and/or recumbency. Gross findings included icterus, hepatomegaly with acinar pattern, serosal hemorrhages, pulmonary edema, and/or fluid content in small and large intestine. Microscopically, all foals had severe, multifocal, necrotizing hepatitis. Necrotizing lymphohistiocytic colitis was observed in 10 of 25 foals, and multifocal necrotizing myocarditis was found in 8 of 25. Gram-negative, Steiner-positive, intracytoplasmic filamentous bacteria were observed in hepatocytes, enterocytes, and myocardiocytes, respectively. PCR detected C. piliforme DNA in the liver (24 of 24), colon (20 of 24), and heart (5 of 25). Our results indicate that necrotic hepatitis is the hallmark of TD in horses; the so-called triad of lesions is not a consistent characteristic of the disease in this species.

Tyzzer 病 (TD) 是由梭菌引起的，一种革兰氏阴性和专性细胞内细菌。该病发生在多个物种中。在某些物种（例如大鼠和小鼠）的 TD 病例中描述了三种病变，即结肠炎、肝炎和心肌炎。我们对 25 例诊断为 TD 的马病例进行了回顾性分析；25 例中有 24 例发生在 <45 天龄的小马驹中；剩下的小马驹是 90 天大。有12男12女；没有关于一只小马驹的性别信息。受影响的品种是夸特马、纯种马、阿拉伯马、油漆马和汉诺威马。大多数病例（25 例中的 19 例）发生在春季。猝死9例；其余动物有腹泻、发烧、腹部膨胀、抑郁、虚弱、无反应和/或卧床。大体检查结果包括黄疸、肝肿大伴腺泡样出血、浆膜出血、肺水肿和/或小肠和大肠中的液体含量。在显微镜下，所有小马驹都患有严重的多灶性坏死性肝炎。在 25 只小马驹中的 10 只中观察到坏死性淋巴组织细胞性结肠炎，在 25 只中的 8 只中发现多灶性坏死性心肌炎。分别在肝细胞、肠细胞和心肌细胞中观察到革兰氏阴性、施泰纳阳性、胞浆内丝状细菌。检测到 PCR肝脏（24 个中的 24 个）、结肠（24 个中的 20 个）和心脏（25 个中的 5 个）中的C. piliforme DNA。我们的结果表明，坏死性肝炎是马 TD 的标志；所谓的病变三联征并不是该物种疾病的一致特征。