Stephen A. C. Hawkins

Risk of oral infection with bovine spongiform encephalopathy agent in primates.

The uncertain extent of human exposure to bovine spongiform encephalopathy (BSE)--which can lead to variant Creutzfeldt-Jakob disease (vCJD)--is compounded by incomplete knowledge about the efficiency of oral infection and the magnitude of any bovine-to-human biological barrier to transmission. We therefore investigated oral transmission of BSE to non-human primates. We gave two macaques a 5 g oral dose of brain homogenate from a BSE-infected cow. One macaque developed vCJD-like neurological disease 60 months after exposure, whereas the other remained free of disease at 76 months. On the basis of these findings and data from other studies, we made a preliminary estimate of the food exposure risk for man, which provides additional assurance that existing public health measures can prevent transmission of BSE to man.

High prevalence of scrapie in a dairy goat herd: tissue distribution of disease-associated PrP and effect of PRNP genotype and age

Following a severe outbreak of clinical scrapie in 2006-2007, a large dairy goat herd was culled and 200 animals were selected for post-mortem examinations in order to ascertain the prevalence of infection, the effect of age, breed and PRNP genotype on the susceptibility to scrapie, the tissue distribution of diseaseassociated PrP (PrP(d)), and the comparative efficiency of different diagnostic methods. As determined by immunohistochemical (IHC) examinations with Bar224 PrP antibody, the prevalence of preclinical infection was very high (72/200; 36.0%), with most infected animals being positive for PrP(d) in lymphoreticular system (LRS) tissues (68/72; 94.4%) compared to those that were positive in brain samples (38/72; 52.8%). The retropharyngeal lymph node and the palatine tonsil showed the highest frequency of PrP(d) accumulation (87.3% and 84.5%, respectively), while the recto-anal mucosa-associated lymphoid tissue (RAMALT) was positive in only 30 (41.7%) of the infected goats. However, the efficiency of rectal and palatine tonsil biopsies taken shortly before necropsy was similar. The probability of brain and RAMALT being positive directly correlated with the spread of PrP(d) within the LRS. The prevalence of infection was influenced by PRNP genetics at codon 142 and by the age of the goats: methionine carriers older than 60 months showed a much lower prevalence of infection (12/78; 15.4%) than those younger than 60 months (20/42; 47.6%); these last showed prevalence values similar to isoleucine homozygotes of any age (40/80; 50.0%). Two of seven goats with definite signs of scrapie were negative for PrP(d) in brain but positive in LRS tissues, and one goat showed biochemical and IHC features of PrP(d) different from all other infected goats. The results of this study have implications for surveillance and control policies for scrapie in goats.

Preliminary Observations on the Pathogenesis of Experimental Bovine Spongiform Encephalopathy

Further preliminary observations are reported of an experiment to examine the spread of infectivity and the occurrence of pathological changes in cattle exposed orally to infection with bovine spongiform encephalopathy. Calves were dosed at four months of age and clinically monitored groups were killed sequentially from two to 40 months after inoculation. Tissues were collected for bioassay, for histopathological examinations and for the detection of PrP. Previous reported observations have included the presence of infectivity in the distal ileum of cattle killed after six to 18 months, the earliest onset of clinical signs in an exposed animal after 35 months, and diagnostic histopathological changes in the brain, in association with clinical disease, after 36, 38 and 40 months. In spite of the relative inefficiency of the bioassay of scrapie-like agents across a species barrier the new observations confirm that the onset of clinical signs and pathological changes in the central nervous system (CNS) occur at approximately the same time. The earliest pathological change, the presence of abnormal PrP 32 months after inoculation, coincided with the earliest detected infectivity in the CNS and occurred shortly before there was evidence of typical spongiform changes in the brain 36 months after inoculation. Infectivity has now been demonstrated in the peripheral nervous system, in the cervical and thoracic dorsal root ganglia 32 to 40 months after inoculation and in the trigeminal ganglion 36 and 38 months after inoculation. At the time of writing evidence of infectivity in other tissues is confined to the distal ileum, not only after six to 18 months but also after 38 and 40 months, but these findings may be supplemented by the results of further mouse assays. Nevertheless, they are in general agreement with current knowledge of the pathogenesis of scrapie.

Pathogenesis of natural goat scrapie: modulation by host PRNP genotype and effect of co-existent conditions

After detection of a high prevalence of scrapie in a large dairy goat herd, 72 infected animals were examined by immunohistochemistry with prion protein (PrP) antibody Bar224 to study the pathogenesis of the infection. Tissues examined included the brain and thoracic spinal cord (TSC), a wide selection of lymphoreticular system (LRS) tissues, the distal ileum and its enteric nervous system (ENS), and other organs, including the mammary gland. The whole open reading frame of the PRNP gene was sequenced and antibodies to caprine arthritis-encephalitis virus (CAEV) infection were determined. Unexpectedly, accumulation of disease-associated PrP (PrPd) in the brain was more frequent in methionine carriers at codon 142 (24/32, 75.0%) than amongst isoleucine homozygotes (14/40, 35.0%). The latter, however, showed significantly greater amounts of brain PrPd than the former (average scores of 9.3 and 3.0, respectively). A significant proportion of the 38 goats that were positive in brain were negative in the ENS (44.7%) or in the TSC (39.5%). These results, together with the early and consistent involvement of the circumventricular organs and the hypothalamus, point towards a significant contribution of the haematogenous route in the process of neuroinvasion. Chronic enteritis was observed in 98 of the 200 goats examined, with no association with either scrapie infection or presence of PrPd in the gut. Lymphoproliferative interstitial mastitis was observed in 13/31 CAEV-positive and scrapie-infected goats; PrPd in the mammary gland was detected in five of those 13 goats, suggesting a possible contribution of CAEV infection in scrapie transmission via milk.

Pathogenesis of experimental bovine spongiform encephalopathy (BSE): estimation of tissue infectivity according to incubation period.

This paper reports the results of tissue infectivity assays of bovine spongiform encephalopathy (BSE) agent in orally exposed cattle at stages during the incubation period. Estimations of the titre of infectivity in central nervous system (CNS), certain peripheral nerve ganglia and distal ileum tissue were made according to time post exposure from the relationship between incubation period and dose for RIII mice and C57bl mice using data from titrations of brain material from cases of BSE. The rate of increase of infectivity in the bovine CNS was then estimated, taking into account these tissue infectivity titres, the variability of the brain titre of clinical field cases of BSE, and the probability density of the expected number of months before clinical onset of each infected bovine. The doubling time for CNS was shown to equal 1.2 months. The titre in the thoracic dorsal root ganglia (DRG) was, on average, approximately 1 log units less than CNS, and cervical DRG approximately 0.5 log less than thoracic DRG. The pattern of increase of infectivity in the distal ileum is that of an initial increase up to 14–18 months post exposure, followed by a decrease, which is likely to be highly variable between animals. These results will be informative for future risk assessments of BSE, especially in relation to reviewing current control measures.

Experimental oral transmission of atypical scrapie to sheep.

Such transmission results in peripheral tissue infectivity that is not detectable by current surveillance screening methods.

Animal Models of Transmissible Spongiform Encephalopathies: Experimental Infection, Observation and Tissue Collection

From the early nineteenth century animal models increasingly contributed to the growing understanding of the nature and causes of infectious diseases [1]. Initially animal experimentation focussed on the demonstration of transmissibility, but the concept of animal models later broadened to encompass any condition found in an animal that is of value in studying a biological phenomenon Animal models range, therefore, from the selection for study of naturally occurring disorders in conveniently managed animal species, to the experimental reproduction of diseases in conventional, or genetically manipulated, host species, or different species. With increasing knowledge has come the universal realisation that experimental infections often differ in important respects from the natural disease they appear to mimic.

Evidence of in utero transmission of classical scrapie in sheep

ABSTRACT Classical scrapie is one of the transmissible spongiform encephalopathies (TSEs), a group of fatal infectious diseases that affect the central nervous system (CNS). Classical scrapie can transmit laterally from ewe to lamb perinatally or between adult animals. Here we report detection of infectivity in tissues of an unborn fetus, providing evidence that in utero transmission of classical scrapie is also possible.

Disease characteristics of bovine spongiform encephalopathy following inoculation into mice via three different routes

Mouse‐adapted transmissible spongiform encephalopathy (TSE) strains are routinely distinguished based on reproducible disease characteristics in a given mouse line following inoculation via a consistent route. We investigated whether different administration routes (oral, intragastric (i.g.) and intracerebral (i.c.)) can alter the disease characteristics in IM mice after serial dilution of a stabilized mouse‐adapted bovine spongiform encephalopathy (BSE) strain (301V). In addition, the infectivity of distal ileum and mesenteric lymph nodes (ln) sampled at three time points (35 days postinoculation (dpi), 70 dpi and terminal disease) after i.g. inoculation of 301V strain was assessed in mice by i.c. challenge. Strain characteristics were assessed according to standard methodology and PrPSc immunohistochemistry deposition patterns. Mean incubation periods were prolonged following oral or i.g. inoculations compared to the i.c. route. Lesion profiles following i.c. challenges were elevated compared to i.g. and oral routes although vacuolation in the dorsal medulla was consistently high irrespective of the route of administration. Nevertheless, the same PrPSc deposition pattern was associated with each route of administration. Distal and mesenteric ln infectivity was detected as early as 35 dpi and displayed consistent lesion profiles and PrPSc deposition patterns. Our data suggest that although 301V retained its properties, some phenotypic parameters were affected by the route of inoculation. We conclude that bioassay data should be interpreted carefully and should be standardized for route of inoculation.