Abstract. A 6-month-old, female, intact Rottweiler dog was presented to the Iowa State University Veterinary Teaching Hospital for a progressive history of abnormal behavior and generalized ataxia. At necropsy, there was eosinophilic infiltration of the brain and spinal cord, most severe in the medulla oblongata, cerebellum, and cervical spinal cord. Infiltrates of eosinophils were also present in the liver and small intestines. The dog was diagnosed with idiopathic eosinophilic meningoencephalomyelitis based on cerebrospinal fluid analysis, histopathology, and special stains to exclude etiologic agents.Key words: Eosinophil; meningitis; meningoencephalomyelitis; Rottweilers.Eosinophilic meningoencephalitis is a rare condition in veterinary medicine; the etiology in the majority of canine cases is often undetermined. Protozoan and nematode parasites can occasionally cause eosinophilic encephalitis in dogs.5 In humans, the most common cause of eosinophilic meningitis is a result of infection with a rat lungworm (Angiostrongylus cantonensis). This infection is usually nonfatal and occurs after ingesting third-stage larvae of the lungworm in contaminated produce or inadequately cooked snails. 7 In the past 2 decades, there have been several reports of an idiopathic form of eosinophilic meningitis that has been shown to affect dogs, cats, and cattle. [1][2][3]6,[8][9][10] In these cases, no infectious etiology has been identified; however, Rottweiler and Golden Retriever dogs appear to be overrepresented, indicating a possible breed predisposition. Dogs with eosinophilic meningoencephalitis often have signs consistent with both brain and spinal cord disease; however, no report has histologically documented the spinal cord changes. In the current report, a young Rottweiler dog with an acute onset of a severe and fatal eosinophilic meningoencephalomyelitis is described.A 6-month-old, 20 kg, female, intact Rottweiler presented to the referring veterinarian with a 6-day history of mild ataxia, lethargy, and decreased appetite. Blood work was performed, including complete blood cell count (CBC) and biochemical profile. The following abnormalities were noted: hypercholesterolemia (328 mg/dl, reference interval: 125-260 mg/dl) and moderate eosinophilia (4,200/ml, reference interval: 0-600/ml). A urinalysis was also performed, which revealed the presence of white blood cells, red blood cells, and bacteria in the sediment. The dog was given clindamycin (300 mg orally, every 12 hr), kept for a few hours for observation, and then sent home. The following day, the dog presented to Iowa State University Veterinary Teaching Hospital (ISU-VTH, Ames, Iowa) with worsening tetraparesis and proprioceptive ataxia.On presentation to the ISU-VTH, the dog was in lateral recumbency, but was quiet, alert, and responsive. On physical examination, the dog had a heart rate of 100 beats per min, a rectal temperature of 40.6uC, and was panting. Generalized muscle tremors were present along with apparent hypersensitivity to touch and sound. On ne...