Natural and experimental oral infection of nonhuman primates by bovine spongiform encephalopathy agents

Abstract

Experimental lemurs either were infected orally with the agent of bovine spongiform encephalopathy (BSE) or were maintained as uninfected control animals. Immunohistochemical examination for proteinase-resistant protein (prion protein or PrP) was performed on tissues from two infected but still asymptomatic lemurs, killed 5 months after infection, and from three uninfected control lemurs. Control tissues showed no staining, whereas PrP was detected in the infected animals in tonsil, gastrointestinal tract and associated lymphatic tissues, and spleen. In addition, PrP was detected in ventral and dorsal roots of the cervical spinal cord, and within the spinal cord PrP could be traced in nerve tracts as far as the cerebral cortex. Similar patterns of PrP immunoreactivity were seen in two symptomatic and 18 apparently healthy lemurs in three different French primate centers, all of which had been fed diets supplemented with a beef protein product manufactured by a British company that has since ceased to include beef in its veterinary nutritional products. This study of BSE-infected lemurs early in their incubation period extends previous pathogenesis studies of the distribution of infectivity and PrP in natural and experimental scrapie. The similarity of neuropathology and PrP immunostaining patterns in experimentally infected animals to those observed in both symptomatic and asymptomatic animals in primate centers suggests that BSE contamination of zoo animals may have been more widespread than is generally appreciated.

Figure 1

(A) Zoo lemur no. 703. PrP deposits in large vacuolated fibers of the ventral funiculus of the cervical spinal cord. Arrows point to fiber membranes. Anti-PrP 3F4, 1:200. (B) Zoo lemur no. 712. Nerve fibers showing PrP immunoreactivity (brown) in layer IV of the cerebral cortex. Anti-PrP 3F4, 1:200. (C) Experimental BSE-infected microcebe no. 656. Microvacuolation in the neuropil of the parietal cortex (layer V). Hematoxylin and eosin. (D) Experimental BSE-infected microcebe no. 656. Abnormal Tau proteins inside pyramidal neurons of the parietal cortex layer III. Anti-tau 961S28T, 1:200. (E) Experimental control microcebe no. 593. High magnification of the stomach wall: no PrP immunoreactivity is detected in the epithelium, secretory glands, or various lymphoreticular tissue elements (arrows). Star indicates luminal surface. Anti-PrP 3F4, 1:200. (F) Experimental BSE-infected microcebe no. 656. PrP distribution in the stomach wall. Arrows point to reticulolymphatic elements; star indicates luminal surface. Anti-PrP 3F4, 1:500. (G) Experimental BSE-infected microcebe no. 656. PrP localization in an intestinal villus. Note the interrupted epithelium at the level of M cells containing a lymphocyte, and the immunoreactivity of lymphoid reticular structures. Stars indicate luminal surfaces. Anti-PrP_106–126, 1:2. (H) Experimental BSE-infected microcebe no. 656. Peyer’s patch with PrP immunoreactive lymphoid structures. Anti-PrP_106–126, 1:2. (I) Experimental BSE-infected microcebe no. 656. PrP labeling in splenic red pulp. Anti-PrP 3F4, 1:500. (J) Experimental BSE-infected microcebe no. 656. Small intestine. Anti-PrP 3F4, 1:200, pre-adsorbed with PrP antigen.