Aerosol and nasal transmission of chronic wasting disease in cervidized mice

Abstract

Little is known regarding the potential risk posed by aerosolized prions. Chronic wasting disease (CWD) is transmitted horizontally, almost surely by mucosal exposure, and CWD prions are present in saliva and urine of infected animals. However, whether CWD may be transmissible by the aerosol or nasal route is not known. To address this question, FVB mice transgenetically expressing the normal cervid PrP(C) protein [Tg(cerPrP) mice] were exposed to CWD prions by either nose-only aerosol exposure or by drop-wise instillation into the nostrils. Mice were monitored for signs of disease for up to 755 days post-inoculation (p.i.) and by examination of tissues for lesions and PrP(CWD) after necropsy. In particular, nasal mucosa, vomeronasal organ, lungs, lymphoid tissue and the brain were assessed for PrP(CWD) by Western blotting and immunohistochemistry. Six of seven aerosol-exposed Tg(cerPrP) mice developed clinical signs of neurological dysfunction mandating euthanasia between 411 and 749 days p.i. In all these mice, CWD infection was confirmed by detection of spongiform lesions and PrP(CWD) in the brain. Two of nine intranasally inoculated Tg(cerPrP) mice also developed transmissible spongiform encephalopathy associated with PrP(CWD) between 417 and 755 days p.i. No evidence of PrP(CWD) was detected in CWD-inoculated Tg(cerPrP) mice examined at pre-terminal time points. These results demonstrate that CWD can be transmitted by aerosol (as well as nasal) exposure and suggest that exposure via the respiratory system merits consideration for prion disease transmission and biosafety.

Fig. 1.

Kaplan–Meier survival plot of Tg(CerPrP) mice exposed to CWD by aerosol (○, black dotted line) versus IN instillation (•, black solid line).

Fig. 2.

(a) PrP^CWD (lanes 3, 4, 6, 7 and 9) in brains of Tg(CerPrP) mice exposed to aerosolized CWD prions demonstrated by WB. Aerosolized sham control (lanes 1 and 2) showing no PrP^CWD. (b) PrP^CWD (lanes 4 and 6) in brains of Tg(CerPrP) mice exposed to CWD prions intranasally demonstrated by WB. Intranasal sham control (lanes 1 and 2) showing no PrP^CWD.

Fig. 3.

IHC from the obex region of the medulla from Tg(CerPrP) mice (×20 magnification). (a) PrP^CWD (arrows) in a mouse exposed to CWD by aerosol versus (b) mouse exposed to sham inoculum. (c) Mouse exposed to CWD by IN route demonstrating PrP^CWD aggregates (arrows) versus (d) mouse exposed intranasally to sham inoculum.

Fig. 4.

(a) Aerosolizing chamber with nebulizer chamber and four plastic enclosures to accommodate anaesthetized Tg(CerPrP) mice. (b) Top view of aerosol chamber with lid removed showing Tg(CerPrP) mice inserted in place to provide nose-only exposure to the chamber (arrow).