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Infectious Prions in the Saliva and Blood of Deer with CWD

##################### Bovine Spongiform Encephalopathy #####################

Subject: Infectious Prions in the Saliva and Blood of Deer with Chronic Wasting Disease
Date: October 5, 2006 at 1:45 pm PST
Infectious Prions in the Saliva

and Blood of Deer with Chronic

Wasting Disease

Candace K. Mathiason,1 Jenny G. Powers,3 Sallie J. Dahmes,4 David A. Osborn,5 Karl V. Miller,5

Robert J. Warren,5 Gary L. Mason,1 Sheila A. Hays,1 Jeanette Hayes-Klug,1 Davis M. Seelig,1

Margaret A. Wild,3 Lisa L. Wolfe,6 Terry R. Spraker,1,2 Michael W. Miller,6 Christina J. Sigurdson,1

Glenn C. Telling,7 Edward A. Hoover1*

A critical concern in the transmission of prion diseases, including chronic wasting disease (CWD)

of cervids, is the potential presence of prions in body fluids. To address this issue directly, we

exposed cohorts of CWD-nai¨ve deer to saliva, blood, or urine and feces from CWD-positive deer.

We found infectious prions capable of transmitting CWD in saliva (by the oral route) and in blood

(by transfusion). The results help to explain the facile transmission of CWD among cervids and

prompt caution concerning contact with body fluids in prion infections.


Deer cohorts 1 (blood), 2 (saliva), and 3

(urine and feces) were electively euthanized at

18 months pi to permit whole-body examination

for PrPCWD. The greatest scrutiny was directed

toward those tissues previously established

to have highest frequency of PrPCWD deposition

in infected deer and generally regarded

as the most sensitive indicators of infection—

medulla oblongata and other brainstem regions,

tonsil, and retropharyngeal lymph node. We

found unequivocal evidence of PrPCWD in brain

and lymphoid tissue of all six tonsil biopsy–

positive deer in cohorts 1 (blood) and 2 (saliva),

whereas all deer in cohorts 3 and 5 were negative

for PrPCWD in all tissues (Table 2 and

Figs. 1 and 2).

The transmission of CWD by a single blood

transfusion from two symptomatic and one

asymptomatic CWDþ donor is important in at

least three contexts: (i) It reinforces that no tissue

from CWD-infected cervids can be considered

free of prion infectivity; (ii) it poses the

possibility of hematogenous spread of CWD,

such as through insects; and (iii) it provides a

basis for seeking in vitro assays sufficiently

sensitive to demonstrate PrPCWD or alternate

prion protein conformers in blood—one of the

grails of prion biology and epidemiology.

The identification of blood-borne prion

transmission has been sought before with mixed

results (9–11). Bovine spongiform encephalopathy

and scrapie have been transmitted to naBve

sheep through the transfer of 500 ml of blood

or buffy coat white blood cells from infected

sheep (12, 13). In addition, limited but compelling

evidence argues for the transmission of variant

Creutzfeldt-Jakob disease (vCJD) through blood

from asymptomatic donors (14–16). Even in

sporadic CJD, PrPres has been found in periph-

eral organs of some patients (17). The present

work helps establish that prion diseases can be

transmitted through blood.

The presence of infectious CWD prions in

saliva may explain the facile transmission of

CWD. Cervid-to-cervid interactions (SOM text),

especially in high density and captive situations,

would be expected to facilitate salivary crosscontact

(11, 18, 19). Salivary dissemination of

prions may not be limited to CWD. Proteaseresistant

prion protein has been demonstrated in

the oral mucosa, taste buds, lingual epithelium,

vomeronasal organ, and olfactory mucosa of

hamsters infected with transmissible mink

encephalopathy (19) and ferrets infected with

CWD (20). Although no instance of CWD

transmission to humans has been detected, the

present results emphasize the prudence of using

impervious gloves during contact with saliva or

blood of cervids that may be CWD-infected.

Environmental contamination by excreta

from infected cervids has traditionally seemed

the most plausible explanation for the dissemination

of CWD (21). However, we could not

detect PrPCWD in cohort 3 deer inoculated repeatedly

with urine and feces from CWDþ deer and examined up to 18 months pi (Table 2).

There are several reasons to view this negative

finding cautiously, including small sample size,

elective preclinical termination, and potential

variation in individual susceptibility that may

be associated with the 96 G/S polymorphism in

the PRNP gene (7, 22). Although no genotype

of white-tailed deer is resistant to CWD infection,

PRNP genotypes S/S or G/S at codon 96

appear to have reduced susceptibility manifest

by longer survival (7). Both deer in cohort 3

(urine and feces) were subsequently shown to

be of the PRNP 96 G/S genotype. Thus, it is

possible, although we think unlikely, that these

deer had a prolonged incubation period (918

months pi) before the amplification of PrPCWD

became detectable in tissues. Recent studies

have shown that PrPres is poorly preserved

after incubation with intestinal or fecal content

(23, 24). Further research using cervid and surrogate

cervid PrP transgenic mice (25) are indicated

to continue to address the presence of

infectious CWD prions in excreta of CWDþ deer and to provide a more substantial basis for

reconsideration of the assumption that excreta

are the chief vehicle for CWDdissemination and


The results reported here provide a plausible

basis for the efficient transmission of CWD in

nature. We demonstrate that blood and saliva in

particular are able to transmit CWD to naBve deer

and produce incubation periods consistent with

those observed in naturally acquired infections

(3, 26). The time from exposure to first detection

of PrPCWD by tonsil biopsy was variable—as

short as 3 months but as long as 18 months (likely

underestimates due to sampling frequency).

The results also reinforce a cautious view of the

exposure risk presented by body fluids, excreta,

and all tissues from CWDþ cervids. ...


CWD AND ENVIRONMENTAL FACTORS i.e. saliva, fecal shedding and fecal-oral transmission is likely


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Subject: [Docket No. FSIS-2006-0011] FSIS Harvard Risk Assessment of Bovine
Spongiform Encephalopathy (BSE)

[Docket No. 03-025IFA] FSIS Prohibition of the Use of Specified Risk
Materials for Human Food and Requirement for the Disposition of
Non-Ambulatory Disabled Cattle

Terry S. Singeltary


TSS Brick Wall,)