Adaptation of the bovine spongiform encephalopathy agent to primates and comparison with Creutzfeldt-- Jakob disease: implications for human health

Abstract

There is substantial scientific evidence to support the notion that bovine spongiform encephalopathy (BSE) has contaminated human beings, causing variant Creutzfeldt-Jakob disease (vCJD). This disease has raised concerns about the possibility of an iatrogenic secondary transmission to humans, because the biological properties of the primate-adapted BSE agent are unknown. We show that (i) BSE can be transmitted from primate to primate by intravenous route in 25 months, and (ii) an iatrogenic transmission of vCJD to humans could be readily recognized pathologically, whether it occurs by the central or peripheral route. Strain typing in mice demonstrates that the BSE agent adapts to macaques in the same way as it does to humans and confirms that the BSE agent is responsible for vCJD not only in the United Kingdom but also in France. The agent responsible for French iatrogenic growth hormone-linked CJD taken as a control is very different from vCJD but is similar to that found in one case of sporadic CJD and one sheep scrapie isolate. These data will be key in identifying the origin of human cases of prion disease, including accidental vCJD transmission, and could provide bases for vCJD risk assessment.

Figure 1

Transmission scheme of TSEs in cynomolgus macaques and C57BL/6 mice. Open frames, natural or accidental disease; hatched frames, experimental disease in primates; stippled frames, experimental disease in mice. IC, intracerebral inoculation; IV, intravenous inoculation; bh, brain homogenate; m^th, month. The incubation periods indicated on the arrows each correspond to one inoculated macaque. One macaque was inoculated with British vCJD (25 months), and the other was inoculated with the first French case of vCJD (30 months). The incubation periods of the i.c. titration are as follows: 10⁻¹ dilution: 20 and 21 months; 10⁻² dilution: 28 months; 10⁻³ dilution: 33 months; 10⁻⁵ dilution: 38 months (the second macaque inoculated presents slight behavioral changes at 48 months after inoculation).

Figure 2

Lesion profiles in C57BL/6 mice after transmission of vCJD, BSE, sCJD, iCJD, and scrapie. Lesion profiles are (a) cattle BSE and British vCJD (two pooled cases); (b) cattle BSE and the first of the three French vCJD cases; (c) cattle BSE and BSE after primary transmission to macaques; (d) cattle BSE and BSE after secondary transmission to macaques; (e) cattle BSE, the mouse-adapted C506 M3 scrapie strain (derived from U.S. sheep scrapie), natural sheep scrapie (two pooled cases from a single French flock); (f) French vCJD and a French case of sCJD; (g) the former sCJD and one French case of iCJD linked to the administration of growth hormone; and (h) same as in g plus the natural sheep scrapie. The dotted lines belong to the lesion profiles of vCJD (in a and b) and of macaque-BSE (in c and d). Vacuolation was scored on a scale of 0–5 in the following brain areas: 1, medulla; 2, pons/mesencephalon; 3, cerebellar cortex; 4, colliculi; 5, hypothalamus; 6, thalamus; 7, hippocampus; 8, septum; 9, cerebral cortex; and 10, striatum.

Figure 3

Electrophoretic analysis of PrPres of vCJD, BSE, sCJD, iCJD, and scrapie transmitted to C57BL/6 mice. Western blot detection of PrPres purified from the brains of C57BL/6 mice at the terminal stage of the disease (except for the control) after inoculation of normal mouse brain homogenate (lane 1); French case of iCJD linked to the administration of growth hormone (lane 2); French case of sCJD (lane 3); first of the three French vCJD cases (lane 4); cattle-BSE (lane 5); and natural sheep scrapie (French Romanov flock) (lane 6). The mouse brain equivalent loads were 0.6 mg (lanes 4 and 6), 1.2 mg (lanes 3 and 5), and 12 mg (lanes 1 and 2).

Figure 4

Immunopathology of BSE, vCJD, and kuru in cynomolgus macaques. All panels show the pattern of PrP deposition with the 3F4 antibody, except f, which depicts glial fibrillary acidic protein immunohistochemistry. (a, b, and c) Thalamus in kuru, BSE, and vCJD, ×20. (d and e) Cerebral cortex in kuru, ×2.5 and ×10. (f) Thalamus in BSE, ×10. (g) Cerebral cortex in BSE (i.v.), ×2.5. (h) Cerebral cortex in BSE (i.c.), ×2.5. (i) Immature florid plaque with a dense core of PrP surrounded by few vacuoles in the cerebral cortex (BSE, i.c.), ×20.