Detection of prions in the faeces of sheep naturally infected with classical scrapie

ABSTRACT: Classical scrapie is a naturally transmitted prion disease of sheep and goats. Contaminated environments may contribute to the spread of disease and evidence from animal models has implicated urine, blood, saliva, placenta and faeces as possible sources of the infection. Here we sought to determine whether sheep naturally infected with classical scrapie shed prions in their faeces. We used serial protein misfolding cyclic amplification (sPMCA) along with two extraction methods to examine faeces from sheep during both the clinical and preclinical phases of the disease and showed amplification of PrPSc in 7 of 15 and 14 of 14 sheep respectively. However PrPSc was not amplified from the faeces of 25 sheep not exposed to scrapie. These data represent the first demonstration of prion shedding in faeces from a naturally infected host and thus a likely source of prion contamination in the environment.     

Brain lesions of naturally occurring pregnancy toxemia of sheep.

The neuropathology and biochemical features of 17 sheep with clinical signs and gross necropsy features of naturally occurring pregnancy toxemia were retrospectively evaluated. The sheep ranged in age from 3 to 6 years and were of seven different breeds and three breed crosses. Thirteen sheep (case Nos. 1-4, 6-9, 11-14, 16) showed astrocytic nuclear swelling, hypertrophy and proliferation, and cerebrocortical neuronal necrosis. Seven of these sheep had Purkinje cell necrosis (case Nos. 2, 3, 6, 11, 12, 14, 16), and seven had vacuolation of cerebral and cerebellar sub-cortical white matter (case Nos. 1-4, 9, 12, 13). The neuropathologic features were similar to those of naturally occurring hypoglycemia of human beings and experimentally induced hypoglycemia of primates and the rat. The lesions seen in the sheep studied may have been caused by cerebral hypoglycemia, but data for blood or cerebral glucose concentrations were not available.     

Laboratory investigation of a naturally occurring outbreak of arthrogryposis-hydranencephaly in Texas sheep

An epizootic of abortions, weak lambs, stillbirths, and congenital arthrogryposis-hydranencephaly occurred in a sheep flock in West Texas. The outbreak began during the first week of January 1987 and continued through the third week of February 1987. Lambs born after February 1987 were not affected. A high incidence of antibodies to Cache Valley virus (Texas 7856 isolate) was demonstrated in the ewes' serum and in precolostral serum from affected lambs. No virus was isolated from tissues and body fluids of the affected lambs. The clinical, pathological, and immunological features of the epizootic were similar to those reported in Akabane virus infection in sheep. Although serological findings strongly suggest Cache Valley virus as the etiological agent of this outbreak, transmission studies are needed.     

Diagnosis of preclinical and subclinical scrapie in a naturally infected sheep flock utilizing currently available postmortem diagnostic techniques.

Scrapie is a naturally occurring transmissible encephalopathy of sheep and goats. Currently available methods for diagnosis are the presence of characteristic histopathologic changes and detection of an abnormal form of prion protein (PrPres) in the brains of affected animals. This study documents preclinical and subclinical scrapie in a flock of 16 sheep utilizing histopathology, immunohistochemistry (IHC), western blot, and electron microscopy (for scrapie-associated fibrils) for confirmation of the disease. Prior to necropsy, none of the sheep showed signs of clinical scrapie. Based on the results of histopathology and positive PrPres tests, 3 ewes were found to have subclinical scrapie. An additional ewe, which did not have histopathologic changes in the brain but was positive by IHC and western blot,was considered a preclinical case of scrapie. None of the sheep had amyloid in the brain stem.     

Lesions and retroviruses associated with naturally occurring ovine pulmonary carcinoma (sheep pulmonary adenomatosis)

Five sheep with ovine pulmonary carcinoma were markedly dyspneic and had sporadic coughing; two had copious watery nasal exudate. In four, lesions consisted of multifocal nodules of neoplastic cuboidal epithelial cells in acinar or papillary patterns. Electron microscopically, cells had microvilli, tight junctions, and cytoplasmic lamellar bodies typical of alveolar type II cells. One sheep had a single lung tumor of nonciliated bronchiolar epithelial cells. Vacuolated alveolar macrophages surrounded adenomatous foci. One sheep had a metastatic lesion in the caudal mediastinal lymph node. All sheep had histologic lesions of lymphoid interstitial pneumonia (LIP, ovine progressive pneumonia) consisting of peribronchiolar and interstitial lymphoid hyperplasia, and fibromuscular proliferation; all had serum precipitating antibodies to ovine lentivirus. Lung fluids or tumor homogenates contained a 26-kd peptide that crossreacted with a primate-derived type D retrovirus as detected by immunoblotting or interspecies competition radioimmunoassay. Ovine lentivirus was isolated from concentrated lung fluids or tumor tissues of four sheep tested and from tumor cell DNA of one animal transfected into ovine muscle cells. These studies document the presence of type D-related retrovirus antigen in ovine pulmonary carcinoma (OPC) in the United States and indicate that lentivirus-induced LIP is a lesion frequently associated with this disease.     

The clinical neurology of scrapie in Irish sheep

One hundred twenty-nine sheep with scrapie were identified from 20 flocks in which scrapie previously had been confirmed. Physical and neurologic examinations were performed on all animals. Videotape recordings were made and reviewed to assess gait. These procedures were repeated in 46 sheep at 2- to 3-week intervals until recumbency or inappetence necessitated euthanasia. Confirmation of scrapie was made by histopathologic and immunohistochemical examinations of brain tissue. The clinical signs most frequently recorded in the 129 animals on initial presentation were hindlimb ataxia (71%), head tremor (61%), altered mental status (57%), positive nibble reflex (51%), crouching posture (51%), teeth grinding (44%), low head carriage (38%), body condition score (BCS) < 1.5 (38%), and conscious proprioceptive deficits of the hindlimbs (36%). Progression of the disease was characterized by an increase in the frequency and severity of ataxia, weakness and hypermetria of the hindlimbs, a decreasing sway response, a decreasing extensor response to thoracolumbar pressure, and a reduction in the BCS. No effect of farm of origin on the clinical presentation could be shown. The presence of a nibble reflex was strongly associated (P < .0005) with prion protein (PrP) genotypes AA136RR154QH171 and AA136RR154QQ171. Logistic regression modeling of groups with associated clinical signs showed that animals with a crouching posture (odds ratio [OR], 20.036) and an abnormal yield to thoracolumbar pressure (OR, 7.117) were at increased risk of ataxia. Pruritus (OR, 0.168) was negatively associated with ataxia. Pruritus (OR, 4.974) and teeth grinding (OR, 4.279) were associated with a positive nibble reflex.     

Brainstem auditory evoked potentials and flash visual evoked potentials in Vietnamese miniature pot-bellied pigs

Brainstem auditory evoked potentials (BAEP) and flash visual evoked potentials (VEP) were recorded from juvenile (5-7 weeks of age) and adult Vietnamese miniature pot-bellied pigs to provide normative data for clinical applications. BAEP responses were collected in response to stimulus intensities of 85, 95, and 105 dB nHL. VEP responses were collected in response to flashes of white light in a darkened room. Left-right ear and left-right eye responses did not differ significantly, and were combined for analysis, with each animal providing two data points for each response. BAEP responses in juvenile subjects were mature, and in all subjects showed the typical pattern of decreasing peak latencies and increasing peak amplitudes with increasing stimulus intensity. VEP responses in juvenile subjects were near to mature values, but the latencies still exceeded those of adults. Differences in response maturation between precocial and altricial species are discussed.     

Evidence for maternal transmission of scrapie in naturally affected flocks

It has been known for many years that the offspring of scrapie affected ewes are at increased risk of developing scrapie but whether this is simply the result of an increased genetic susceptibility or transmission of infection has always been unclear. To contribute to clarify this we analysed the data collected in a detailed study of scrapie occurrence in a number of naturally affected commercial sheep flocks in Great Britain (GB) to investigate the association between PrP genotype and parental scrapie status and the incidence of scrapie. Our analyses confirmed the strong association between PrP genotype and the incidence of scrapie found in previous studies and a low incidence of scrapie in animals carrying the ARR allele and a high risk in homozygous VRQ animals. However, we also demonstrate an increased incidence of scrapie in the offspring of scrapie affected ewes controlling for the confounding effect of PrP genotype, but no increased scrapie incidence in the offspring of scrapie affected sires. Our results suggest that some of the increased incidence of scrapie in the offspring of scrapie affected ewes is the result of transmission of infection from mother to offspring. Our results confirm that a breeding policy aimed at decreasing the genetic susceptibility of the population should decrease the incidence of scrapie and that removing the offspring of scrapie affected animals from affected flocks could contribute to the control of this disease.