Bovine spongiform encephalopathy in an adult British Friesian cow

The pathological and molecular but not clinical phenotypes are maintained after second passage of experimental atypical bovine spongiform encephalopathy in cattle

Background

Atypical bovine spongiform encephalopathies (BSEs), classified as H-type and L-type BSE based on the Western immunoblot profiles, are naturally occurring diseases in cattle, which are phenotypically different to classical BSE. Transmission studies in cattle using the intracerebral route resulted in disease where the phenotypes were maintained irrespective of BSE type but clinically affected cattle with a shorter survival time displayed a nervous form whereas cattle with a longer survival time displayed a dull form. A second transmission study is reported here where four cattle were intracerebrally inoculated with brain tissue from experimentally infected cattle presenting with either the nervous or dull form of H- or L-type BSE to determine whether the phenotype is maintained.

Results

The four inoculated cattle were culled at 16.5-19.5 months post inoculation after presenting with difficulty getting up, a positive scratch response (all) and dullness (three cattle), which was not observed in two non-inoculated control cattle, each housed with either group of inoculated cattle. Only the inoculated cattle had detectable prion protein in the brain based on immunohistochemical examination, and the Western immunoblot profile was consistent with the H-type or L-type BSE of the respective donor cattle.

Conclusions

Second passage of H-type and L-type BSE in cattle produced a TSE where the majority of cattle displayed the dull form regardless of clinical disease form of the donor cattle. The pathological and molecular phenotypes of H- and L-type BSE were maintained.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-014-0243-2) contains supplementary material, which is available to authorized users.

Clinical findings in 78 suspected cases of bovine spongiform encephalopathy in Great Britain

The clinical findings in 59 cows with bovine spongiform encephalopathy (BSE) were compared with those in 19 cattle that were submitted as BSE suspects but not confirmed by immunohistochemistry. Both groups were also compared with a control group of 20 healthy cows. Abnormalities in behaviour, temperament, mental status and activity, neurogenic disorders of gait and hyperreactivity to touch were frequently observed in the cattle with BSE. Not every animal with BSE displayed clinical signs in all these categories, and the severity of the signs was not always useful for differentiating them from the BSE suspects that were not confirmed by pathology. The neurological examination was better than passive observations for the clinical diagnosis of BSE. Tests of the animals' responses to sudden auditory, visual and tactile stimuli were very useful for distinguishing cases of BSE from unconfirmed BSE suspects if the cases did not display signs in all the categories.

Aspects of the metabolism of dairy cows during the incubation of bovine spongiform encephalopathy

As part of a nutritional study lasting from six weeks before calving to 22 weeks of lactation, blood samples collected from 47 dairy cows maintained under well-defined conditions were analysed for a variety of metabolites and hormones. At various times after the completion of the study, six of the animals developed clinical signs of bovine spongiform encephalopathy (BSE), although when they were sampled it was not known that they were incubating the disease. The data were used to make comparisons between the animals that developed BSE and those that did not develop the disease and which had been maintained under the same conditions. The greatest differences between the animals incubating BSE and the control animals were observed at times of nutritional stress, at the start of lactation and when the intake of concentrate feeds was reduced at week 13 of lactation. In the animals that subsequently developed BSE, feed intakes were lower in early lactation; plasma beta-hydroxbutyrate concentrations were significantly higher (P<0.001) at weeks 3 and 5 of lactation; adjusted milk yields were lower until week 6 of lactation and milk fat concentrations were consistently lower. There was no effect on plasma glucose concentrations, although insulin concentrations were significantly lower in week 1 of lactation (2-27 v 2.50 microiu/ml) (P<0.05). The concentrations of plasma proteins and urea were unaffected by BSE incubation, apart from protein concentrations being significantly higher one week before calving, and the concentration of urea being significantly lower five weeks before calving. The plasma concentrations of somatotrophin, prolactin, oestradiol and progesterone were similar in the two groups of animals throughout the study. The differences observed indicate that the energy metabolism of dairy cows incubating BSE may be subtly altered before the onset of clinical signs of the disease.

Reflections on scrapie and related disorders, with consideration of the possibility of a viral aetiology

The transmissible spongiform encephalopathies of domesticated animals, scrapie in sheep and bovine spongiform encephalopathy (BSE), and transmissible mink encephalopathy are more than a scientific curiosity; under certain circumstances their impact on commercial activities can be calamitous. Knowledge of their causation and pathogenesis is still rudimentary, but many consider than an unconventional agent, the prion (a brain protein, PrP), that is not associated with nucleic acid is involved in both. Others believe that conventional viruses, which replicate by virtue of their nucleic acid-defined genes, are involved in the causation and progression of the encephalopathies but that technical problems have prevented their identification. Others postulate even more exotic causative agents. While this paper will particularly address the possibility of a viral aetiology for these diseases, it is also emphasized that our knowledge of the state of the immune system in animals with encephalopathy needs broadening. There are remarkable gaps in our knowledge of the histopathology of these diseases, particularly the nature of the characteristic vacuoles. Much further work is needed on the biochemical changes in the brain and the serum, particularly of the latter as it could lead to an additional means of recognizing clinical cases without waiting for the animal to die with subsequent examination of the brain for characteristic lesions and the presence of protease-K-resistant PrP.

Animal spongiform encephalopathies--an update. Part II. Bovine spongiform encephalopathy (BSE)

An update on animal spongiform encephalopathies other than BSE was presented in part I of this article. Part II of this article focuses on bovine spongiform encephalopathy (BSE). The article describes clinical signs, histological and other changes leading to a diagnosis, the differential diagnosis, and the prospects for pre-clinical diagnosis of this disease. It describes the origin and course of the epidemic in the UK and discusses the question why it is only the UK which has witnessed such a large-scale epidemic. Predicted to arrive much earlier, the epidemic now finally seems to have passed its peak. The article goes on to discuss the chance of the disease occurring in a country like the Netherlands and the measures taken to prevent and control the disease, should it occur. The article concludes with a discussion of what has been found with regard to genetic factors, the results of experimental and unintentional artificial transmission of BSE to various species, and possible implications for human health.

Comparative ultrastructural neuropathology of naturally occurring bovine spongiform encephalopathy and experimentally induced scrapie and Creutzfeldt-Jakob disease

We report the ultrastructural neuropathology of bovine spongiform encephalopathy (BSE), a recently described slow virus disease first recognized in Friesian/Holstein cattle, and compare it to that of experimental scrapie and Creutzfeldt-Jakob disease. The spongiform change, which was most pronounced in the central grey matter of the midbrain, consisted of membrane-bound vacuoles within neuronal processes, containing curled membrane fragments, secondary chambers and vesicles. Axons and dendrites accumulated whorls of neurofilaments and other subcellular organelles, such as mitochondria and dense bodies, which were entrapped within the filamentous masses. Other neurites accumulated electron-dense bodies, and still others electron-lucent cisterns and branching tubules. Membrane-bound neuronal inclusions, composed of tubules measuring 10 nm in diameter, were found in axonal terminals. Tubulovesicular structures were loosely packed and were occasionally surrounded by a common membrane, a finding previously described only in natural scrapie in sheep. Except for the intraneuronal inclusions, all of the ultrastructural features of BSE resembled those found in scrapie and Creutzfeldt-Jakob disease.

Some problems of diagnosis of the spongiform encephalopathies in ruminants

The difficulties of a positive diagnosis in the spongiform encephalopathies based only on epidemiological and clinical data are briefly reviewed. However, in B.S.E. as in scrapie, the epidemiology and the clinical data may frequently suggest these diseases. The main diseases which must be taken into account in the differential diagnosis of both spongiform encephalopathies are discussed and the criteria of the differential diagnosis are tabulated.