November 1, 2001
A Question and Answer Regarding CHRONIC WASTING DISEASE,
CERVIDS - USA (COLORADO)
Q. CWD is the elk and deer equivalent of 'mad cow disease' (BSE),
thought to be caused by a similar prion infective agent. Previous postings
to ProMED-mail have expressed concerns that CWD can be transmitted from
livestock to wild populations. Considering that the source and spread of BSE
among livestock is thought to be related to the feeding of offal to those
animals, why then is it thought that CWD can be transmitted otherwise? Has
it been determined that it can be transmitted laterally/passively from one
individual to the next?
A. [There is some evidence BSE can be transmitted to the offspring, while in
utero. Likewise, perhaps, from consumption on the grass, after it has passed
through the animal. Based upon the BSE experience, it is believed to be the
same with CWD. - Mod.TG]
Q. If not, why then are whole herds of livestock being wiped out in a
reaction similar to the cull of animals in Europe following the FMD epidemic
A. [Please see the answer to the question above. - Mod.TG]
Q. How different is it then from other TSEs?
A. [There are a number of subtle differences between the different TSE's.
The appearance of the lesions, the location of the codons, and probably many
other unknowns because there is not a lot of research in CWD. - Mod.TG]
Q. Bearing in mind that CWD has been detected in wild deer and elk for over
30 years, and if it can be transmitted passively, it is possible that an
outbreak in domestic animals could have arisen from contact with wild
animals -- wouldn't fears of transmission to wildlife then be over-reactive?
i.e., it would not be outside the normal ecological cycle.
A. [A good question for which there is no answer, presently. - Mod.TG]
Q. If the origin of CWD is in the wild populations, and at least 30 years
old, one could infer that this origin has been 'natural,' i.e., not caused
by forced feeding of offal. Theories that it arose from wild animals who
chewed bones of dead animals to obtain mineral supplement would seem
illogical, assuming that this behaviour is probably as old as the species
themselves and CWD has apparently not caused an ecological disturbance
before (and does not do so now?). Therefore, epidemiology of transmission
notwithstanding, couldn't BSE and other
TSEs also have originated naturally?
A. [This has always been a speculation, yet remains to be proven.
Conor E. Kretsch