From what I know about it, CWD has always been around, but not very prevalent until the deer ranchers got too big. The disease shows up in feed lots and is spread by the infected deer being close to non-infected deer. People feeding deer can help spread it too when an infected deer escapes the feed lot and mingles with the wild population.
Here in MO the deer ranchers are trying to get themselves out from under the DNR and want to be managed by the farm bureau like cattle ranchers. That would be the worst possible thing to happen IMO since the farm bureau has no idea how to control CWD, but the DNR does...
There is a human form of prion disease called vCJD. If one reads CWD stories, we always see the warning that CWD is not transmissible to humans, but there are some cases where a linkage might be made. The problem is that due to changes in insurance and cost, it is rare that autopsies are done in hospital deaths unless there are medico-legal questions or done as part of a research study.
The gold standard for identifying prion disease can only be done after death. It necessitates the testing of brain tissue by immunological staining. There are other tests (such as the tonsular test done on deer), but this test only shows that an animal is negative at that time and the amount of prion is at an undetectable level.
CWD was first observed in a research deer herd that was kept on land that had been previously used to keep scrapie positive sheep. The concentration levels may have been enough to cause the abnormal sheep prions to cross the specie barrier, but that has never been determined. Some deer from that facility escaped into the wild and probably became vectors to the wild population.
It has been demonstrated that CWD is spread by urine, feces and nasal secretion contact. There is a very very high correlation between the spread of CWD (especially east of the Mississippi River)due to cervid farming. This has lead to the regulation about transporting animals for breeding purposes on game farms. Some states prohibit importation from outside of their state.
Because it has been shown that urine can contain and spread CWD prions, one has to question the ethics of hunters using urine based scent lures since their source comes from an identifiable source of CWD spread. Remember: there is no test that can tell if a deer is CWD negative...only that the level of prion is below detectable levels.
Prions, once they become part of the environment, will remain there for a very long time and remain a source of infection. Research with a scrapie positive sheep farm in Iceland shows just how persistent prions are once in the soil. In this case, the scrapie positive sheep were removed, the land left fallow for over a year, the top 6" of soil removed and land chemically treated. Negative sheep were reintroduced and members of the herd came down with scrapie within a short time.
Cold, heat, rain, snow...do not decontaminate the land. Prions are hardy little buggers.
This was aptly demonstrated in Great Britain when mad cow disease became rampart. Downer cattle (BSE positive)were rendered into protein feed supplement which was feed to cattle, which subsequently became infected. The process of producing the protein supplements from downer cattle include moist high heat which did not destroy the prions. Studies have shown that they can survive in normal cooking processes.
This is how vCJD arose in many in Europe...eating BSE beef. In Europe, this passage between species probably had a lot to do with diet...blood sausages, brains and neural tissue as part of many meat products.
Lab studies of prion disease have demonstrated much of how these diseases are passed. It is certain that urine, feces, mucosal secretions,and ingestion are all routes of infection. Progression usually goes from the gut into the lymphatic system and then up the spinal column.
This has lead to the recommendation that in field dressing and butchering wild game that one avoid cutting the spinal column and care taken when handling brains (for those who brain tan...wear gloves!!). More so, it is suggested that one debone game rather than cutting through marrow with band saws as most butchers do.
Once CWD is seen in an area, it will remain there and (depending on concentration of deer)may well expand. To lessen the chances, I would never ever use any urine based lures because the chance of contaminating ones hunting areas with products from what have been demonstrated sources seems very unethical to me.
Here in MI, we have had only one identified case of CWD and it was linked to a cervid farming operation.
I've been reading and studying prion diseases for a number of years. ProMed has a newsletter that provides reports of CWD instances and research. I have also been in communication with several people involved in research. Lots of new and sensitive testing techniques have been developed in the lab, but not applicable to routine testing. DCPAH at MSU does yearly screening of lymph nodes from deer harvested by hunters every year. Most states now have similar programs to identify occurrence of this and other diseases.
Be glad to try and answer any specific questions...feel free to PM me.
jack
