Sarcocystosis with involvement of the central nervous system in lambs.

Abstract

An outbreak of neurologic disease in a flock of 5-month- taining large rounded metrocytes and early bradyzoites, and old Rambouillet lambs on a sheep farm in west-central In- were associated with some degree of myositis with degendiana was investigated. Over a 4-week period during the eration of muscle fibers and lymphocytic perimysial infiltrasummer of 1990, 32 of 48 lambs in 1 pen were affected, and tion. 22 of these lambs died. Approximately 300 sheep were on Multifocal, nonsuppurative meningoencephalomyelitis was the farm. The affected lambs were confined to a single pen evident in the cerebrum, cerebellum, brain stem, and cerin a large open-sided pole barn and were the youngest group vital, thoracic, and lumbar spinal cord of all 3 lambs (Fig. of spring lambs on the farm. 1). Inflammation was characterized by glial nodules, multiClinical signs described by the owner and referring vet- focal necrosis with gliosis and mononuclear cell infiltration, erinarian included anorexia, weight loss, incoordination, stiff and lymphocytic infiltration around blood vessels and in the limbs, trembling, and generalized weakness. The condition meninges (Fig. 2). An immature schizont was found in the progressed rapidly in fatal cases, and death generally occurred pons of 1 of these lambs (Fig. 3). The density of neuroglia within 7 days of the onset of clinical signs. around this schizont was increased, but the schizont was not Three clinically affected lambs (2 live and 1 dead) were surrounded by microglia. Immunohistochemical examinasubmitted to the Animal Disease Diagnostic Laboratory, tion of paraffin-embedded sections of samples of brain from Purdue University, West Lafayette, Indiana, for diagnostic all 3 lambs using antisera to Toxoplasma gondii, Neospora evaluation. Both live lambs were thin, weak, and ataxic. All caninum, and Sarcocystis spp. was negative. 11 The FA test 3 lambs had bronchopneumonia of varying severity. One for pseudorabies was negative, and no viral agent was isolamb had moderate subcutaneous edema of the neck and lated. inguinal region and mild serous effusions in the pleural, peri- The small intestine of 1 lamb was infected by coccidia and cardial, and peritoneal cavities. Tissue samples from all 3 cryptosporidia. After the diagnosis of intestinal coccidiosis lambs were routinely processed for histopathologic exami- was conveyed, the referring veterinarian directed the owner nation. Samples of pneumonic lung were inoculated on blood to add amprolium to the lambs’ feed. Following treatment, and MacConkey’s agar in an attempt to culture for aerobic affected lambs improved clinically, no more died, and no bacteria. Selected areas of the pneumonic lungs were ex- additional lambs developed clinical signs. amined for bovine respiratory syncytial virus (BRSV), in- Approximately 6 weeks later, a team of diagnostic perfectious bovine rhinotracheitis virus (IBR), and sonnel visited the farm for an on-site evaluation, to collect Parainfluenza-3 virus (P13) by direct immunofluorescence convalescent sera from affected and nonaffected lambs, to (FA) and were inoculated onto bovine turbinate cells for virus collect fecal samples from dogs, and to choose a convalescent isolation. A portion of the brain from 1 of the live lambs lamb for further diagnostic evaluation. was examined for pseudorabies virus by FA and was also Hay was found stacked in 1 comer of the pole barn, and inoculated onto cell cultures. grain was stored in uncovered wooden bins at the opposite