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.