Chronic wasting disease (CWD) is an emergent, rapidly spreading prion disease of 
cervids. Shedding of infectious prions in saliva and urine is thought to be an 
important factor in CWD transmission. To help to elucidate this issue, we 
applied an in vitro amplification assay to determine the onset, duration, and 
magnitude of prion shedding in longitudinally collected saliva and urine samples 
from CWD-exposed white-tailed deer. We detected prion shedding as early as 3 
months after CWD exposure and sustained shedding throughout the disease course. 
We estimated that the 50% lethal dose (LD50) for cervidized transgenic mice 
would be contained in 1 ml of infected deer saliva or 10 ml of urine. Given the 
average course of infection and daily production of these body fluids, an 
infected deer would shed thousands of prion infectious doses over the course of 
CWD infection. The direct and indirect environmental impacts of this magnitude 
of prion shedding on cervid and noncervid species are surely significant.
IMPORTANCE: Chronic wasting disease (CWD) is an emerging and uniformly fatal 
prion disease affecting free-ranging deer and elk and is now recognized in 22 
U.S. states and 2 Canadian provinces. It is unique among prion diseases in that 
it is transmitted naturally through wild populations. A major hypothesis to 
explain CWD's florid spread is that prions are shed in excreta and transmitted 
via direct or indirect environmental contact. Here we use a rapid in vitro assay 
to show that infectious doses of CWD prions are in fact shed throughout the 
multiyear disease course in deer. This finding is an important advance in 
assessing the risks posed by shed CWD prions to animals as well as humans.