Wednesday, December 17, 2008




MEETING DATE: December 10, 2008 AGENDA

TITLE: Chronic Wasting Disease Study Results

PRESENTERS: Open Space and Mountain Parks Michael D. Patton, Director Heather M. Swanson, Wildlife Ecologist Colorado Division of Wildlife Michael W. Miller, Senior Wildlife Veterinarian


Chronic wasting disease (CWD) is a fatal prion disease occurring in mule deer inhabiting Open Space and Mountain Parks (OSMP) properties. Beginning in 2005, OSMP and the Colorado Division of Wildlife (CDOW) undertook a 3 year research project to examine CWD on OSMP and private property in the Table Mesa area to increase the understanding ofCWD and possibly CWD management. During the course of the study, 131 mule deer were captured and collared and 115 adult deer were monitored. Each deer was tested for CWD status once per year using either tonsil or rectal mucosa biopsy (both techniques developed for testing live animals). In addition, a mark-resight census was performed (visual counts of collared and un-collared deer within the study area are analyzed using a population census model to estimate overall population size) annually to estimate the population of mule deer residing in the study area.

OSMP and CDOW staff participants found CWD prevalence within the study area (south Boulder between Baseline, Eldorado Springs Drive, Broadway and the Flatirons mountain front) to be surprisingly high - overall approximately 29 percent of the deer sampled were infected. Staff also found that average survival time for infected deer was significantly lower than for uninfected deer. Cause of death varied somewhat between years, but the most common mortality causes were mountain lion predation, clinical CWD and vehicle collisions. Mark-resight inventory estimations of the deer population within the study area showed a decrease in local deer numbers over estimates derived from census efforts in the late 1980s. The high prevalence, low survivorship, and decreasing population numbers suggest that CWD is having a measurable effect on the mule deer herd living in south Boulder. High prevalence makes previously discussed management actions such as test­and-cull control unlikely to be feasible.



This is an information item only. No action is requested from the Board at this time.


Economic: The Open Space and Mountain Parks program contributes to the economic vitality of the city because it provides the setting and services that help to attract a diversity of businesses and to recruit and retain employees. As a result, understanding of wildlife health issues on OSMP properties is crucial.

Environmental: The extent of CWD infection and associated deer population declines are likely to have some impact on the environment due to the importance of mule deer as large herbivores on OSMP properties. The overall impact of this is presently unknown.

Social: Wildlife on OSMP support a quality visitor experience and so understanding of disease impacts on wildlife populations is important to maintain a quality visitor experience. Declines in deer populations may diminish the visitor experience by reducing opportunities to view and enjoy mule deer. Because no human health threat has been identified for CWD, direct impacts to the citizens of Boulder are unlikely.


Fiscal: OMSP funded the study in conjunction with the CDOW. Overall expenditures over 3 years totaled approximately $60,000 in non-staff expenses. CDOW contributed significant funding well beyond that provided by OSMP. Field work was supplemented by funds from the US Department of Agriculture, Animal and Plant Health Inspection Service, Veterinary Services.

Staff time: Staff time included time spent as part ofthe normal work plan of the wildlife ecologist and rangers. Approximately 1.5 seasonal employees were hired specifically to work on the CWD study including capture and monitoring of deer. CDOW provided staffing similar to or in excess of what OSMP contributed.


At the beginning of the study, several members ofthe public spoke in favor of the study before the Open Space Board of Trustees (OSBT). At that time, the study also received significant media attention including two stories on 9News and one in the Daily Camera. Since the initial start-up phase, no formal public comment has been received; however, numerous informal individual public contacts have been made in the course of conducting field work over the last 3 years. This presentation, as well as a presentation to the Colorado Wildlife Commission, will provide the public with a summary of the results of the study. The primary results of the study recently have been accepted for publication, and additional publications featuring other aspects of the data are likely in the future. Dr. Charles Southwick, professor emeritus at CD Boulder has been involved in consultation throughout the study and appears as a co-author on the submitted study results paper.

ANALYSIS: Chronic wasting disease is a prion disease occurring in several members of the cervid family including mule deer, white-tailed deer, elk and moose. Presence of CWD in Boulder mule deer was first detected in 1997, but local prevalence had not been estimated prior to our study. In an effort to understand prevalence and the possible impact of CWD on Boulder and other Front Range deer populations as well as contribute to the broader understanding of CWD in wild cervids, the CDOW proposed a study to examine CWD in mule deer found on OMSP lands and surrounding residential areas in south Boulder.

In summer 2005, OSBT approved the study of CWD on OSMP properties in conjunction with the CDOW. The original memo and study plan are attached (Attachments A and B). Since that time, the OSMP and CDOW staff participants have completed 3 full years ofthe study including capturing 131 deer. Captured deer were tested for CWD and fitted with a radio collars for monitoring. Age was estimated from tooth wear and blood samples were collected for additional analysis. Deer were monitored throughout the year to determine location, condition and cause of death for individuals that died. Beginning the week of December 8, 2008, the staffs will begin to recapture the 24 remaining, test-negative deer to remove their collars as the batteries begin to malfunction. The 4 positive deer will continue to be monitored as long as their collars function.

During each year of the study, a mark-resight inventory of deer residing within the study area during late November and early December was also completed. These data were analyzed to provide overall population estimates within the study area and were compared between years and to earlier data (1987-2001.) collected in this same area using similar methods.


Prevalence among the male deer sampled was 41 percent, about twice the prevalence among the adult females (20 percent). Life expectancy for uninfected deer was approximately 3 times longer than for infected deer. Main causes of death for infected deer were death from "chronic wasting" syndrome and predation by mountain lions. Mountain lions were more likely to kill infected animals than uninfected animals although this effect varied over years and seemed to be impacted by management of mountain lions in the area. The combination of high infection rates and relatively low survival of infected deer would be expected to cause a decline in deer abundance over time, and the observed trends in deer abundance around Table Mesa appear consistent with these predictions: the occurrence of chronic wasting disease in this population over the last two decades (based on historical field records and observations) has coincided with a measurable decline in estimated deer abundance in this area since the late 1980s.

Next Steps:

Based on the information collected as part of this study, the deer population in south Boulder is predicted, based on population-disease models, to continue to remain low or possibly decline further. However, lack of complete understanding of prion diseases makes this future uncertain. Based on the high prevalence detected, previously discussed management actions such as test and cull are not recommended. Under the circumstances, this situation may best serve as an opportunity to watch and learn how prion disease affects


wild populations over the long term. Follow-up studies looking at population and prevalence trends would be of value in refining predictive models of CWD and its potential control. Although current options for management of the disease are limited, experimental examination of potential management actions still could be considered. Future cooperation between OSMP and CD OW to study the population or experimental management actions will depend on interest and funding availability for both agencies.

Because CWD appears to be negatively impacting this deer population, minimizing additional adverse effects will be important to help maintain the overall viability ofthis population. Residential development within deer habitat already has been minimized by the presence of OSMP lands, but possible improvement of available habitat quality may merit consideration. Increased disturbance/stress from humans, including disturbance from recreational use (on OSMP, deer have been shown to be sensitive to recreational use­Miller et al. 2001 and Germaine, et al. unpublished data) also may influence habitat use and deer behavior, and these influences also may merit consideration in the context of CWD and overall deer population management.

Although the implications of our findings for the deer population are disconcerting, the study was a success from a scientific and agency cooperation standpoint. No free-ranging mule deer population with CWD has previously been studied in this way, making these data quite valuable in improving the overall understanding of CWD in wild deer populations. The Table Mesa deer population may provide an important opportunity to examine the long-term effects of CWD infection in a wild population. The study logistics went well and cooperation between OSMP and CDOW proved to be extremely beneficial; many strong collaborative relationships were built through the study; including those that led to the current mountain lion study occurring on OSMP properties, making future cooperation likely.

Submitted by:

Michael D. Patton, Director

Heather M. Swanson, Wildlife Ecologist


A. Original OSBT memo dated July 27,2005

B. Original study plan

One-third of Boulder’s deer infected

Depth of chronic wasting disease means culling no longer an option, experts say

By Ryan Morgan (Contact)
Originally published 08:40 p.m., December 16, 2008
Updated 08:40 p.m., December 16, 2008

A new study shows one out of three mule deer in south Boulder suffers from chronic wasting disease — and those results mean the traditional approach of killing infected animals to fight the disease probably won’t work, researchers say.

“Everything that’s been tried to control chronic wasting disease really fails in the face of that kind of infection rate,” said Heather Swanson, a wildlife ecologist for Boulder’s Open Space and Mountain Parks Department.

In a memo to city leaders, Boulder’s open space officials said they no longer favor killing to deal with chronic wasting disease. The Boulder City Council, which can also set land-management policies for the city’s open space properties, hasn’t yet weighed in on the matter.

Researchers from the Colorado Division of Wildlife and the city teamed up starting in 2005 to study the mule deer population — the first study of its kind to take place in Boulder, Swanson said. The study focused on deer in an area bordered by Baseline Road on the north, Eldorado Springs Drive on the south, Broadway on the east and the Flatirons on the west.

During the study, ecologists tranquilized 115 mule deer, affixed them with radio collars and tested them for chronic wasting disease, an affliction similar to “mad cow disease,” in which misfolded proteins riddle an animal’s brain with holes, eventually killing it.

They found that overall, 29 percent of the deer tested had the disease. Those animals on average died much sooner than non-infected deer, and they often fell prey to mountain lions. Swanson said many of the infected deer preyed upon by cougars didn’t show symptoms that were obvious to human researchers.

“The mountain lions seem to be much better at detecting it,” she said.

Forty-one percent of male mule deer were infected, compared with 20 percent of females, because males cover more territory, which puts them at higher risk of being exposed to the disease, Swanson said.

Scientists still don’t know exactly how chronic wasting disease is transmitted, although researchers suspect it’s passed on from the urine, feces or saliva of infected animals. Swanson said some research suggests that the prions may stick to clay soils as well.

For the past several years, land managers have consistently said the best way to curb the spread of chronic wasting disease is to find infected animals and kill them. But killing one-third of any deer population isn’t a realistic approach, Swanson said, and could do more harm than good.

Diseased animals can still reproduce, thereby contributing to the health of the population, she said — something they wouldn’t be able to do if they were killed as soon as they were shown to be infected.

“With a population that’s in a precipitous decline, removing that large of a number of animals probably isn’t a good idea,” she said. “They may still be contributing to the population” before dying of the disease.

In the memo to the Boulder City Council, open space scientists said the disease has resulted in fewer deer in and around Boulder.

“The occurrence of chronic wasting disease in this population over the last two decades ... has coincided with a measurable decline in estimated deer abundance in this area since the late 1980s,” according to the memo.

Swanson said scientists are hoping ever-increasing numbers of deer don’t get infected, and she said some models of the disease predict the infection rate should level off soon. That’s because chronic wasting disease is thought to require a certain level of deer density to spread quickly — once sufficient numbers of deer die, that density is depleted and the rate of infection slows.

That’s the hope, anyway. Swanson said there’s really only one way to know for sure.

“At this point, we’re just recommending that we watch the population and see what happens,” she said.

DISTURBING to me is the fact no one seems to be concerned with the mountain lions or cougars and the potential for transmission of CWD to those species in the wild, which we know is very possible, if not already happened. ...

Species Born Onset/Died
Ocelot May 1987 Mar 1994
Ocelot Jul 1980 Oct 1995
Puma 1986 May 1991
Puma 1980 May 1995
Puma 1978 May 1995
Lion Nov 1986 Dec 1998
Tiger 1981 Dec 1995
Tiger Feb 1983 Oct 1998
Ankole 1987 May 1995
Ankole 1986 Feb 1991
Bison 1989/90 Oct 1996

Maff data on 15 May 99
kudu 6
gemsbok 1
nyala 1
oryx 2
eland 6
cheetah 9
puma 3
tiger 2
ocelot 2
bison 1
ankole 2
lion 1


North American Cervids Harbor Two Distinct CWD Strains


Angers, R. Seward, T, Napier, D., Browning, S., Miller, M., Balachandran A., McKenzie, D., Hoover, E., Telling, G. 'University of Kentucky; Colorado Division of Wildlife, Canadian Food Inspection Agency; University Of Wisconsin; Colorado State University.


Despite the increasing geographic distribution and host range of CWD, little is known about the prion strain(s) responsible for distinct outbreaks of the disease. To address this we inoculated CWD-susceptible Tg(CerPrP)1536+/· mice with 29 individual prion samples from various geographic locations in North America. Upon serial passage, intrastudy incubation periods consistently diverged and clustered into two main groups with means around 210 and 290 days, with corresponding differences in neuropathology. Prion strain designations were utilized to distinguish between the two groups: Type I CWD mice succumbed to disease in the 200 day range and displayed a symmetrical pattern of vacuolation and PrPSc deposition, whereas Type II CWD mice succumbed to disease near 300 days and displayed a strikingly different pattern characterized by large local accumulations of florid plaques distributed asymmetrically. Type II CWD bears a striking resemblance to unstable parental scrapie strains such as 87A which give rise to stable, short incubation period strains such as ME7 under certain passage conditions. In agreement, the only groups of CWD-inoculated mice with unwavering incubation periods were those with Type I CWD. Additionally, following endpoint titration of a CWD sample, Type I CWD could be recovered only at the lowest dilution tested (10-1), whereas Type II CWD was detected in mice inoculated with all dilutions resulting in disease. Although strain properties are believed to be encoded in the tertiary structure of the infectious prion protein, we found no biochemical differences between Type I and Type II CWD. Our data confirm the co·existence of two distinct prion strains in CWD-infected cervids and suggest that Type II CWD is the parent strain of Type I CWD.

see page 29, and see other CWD studies ;

Sunday, November 23, 2008

PRION October 8th - 10th 2008 Book of Abstracts

Biochim Biophys Acta. Author manuscript; available in PMC 2008 December 9. Published in final edited form as: Biochim Biophys Acta. 2007 June; 1772(6): 681-691. Published online 2006 December 15. doi: 10.1016/j.bbadis.2006.12.006. PMCID: PMC2597801 NIHMSID: NIHMS25810

Copyright notice and Disclaimer

The prion strain phenomenon: Molecular basis and unprecedented features

Rodrigo Morales,1,2 Karim Abid,1 and Claudio Soto1# 1 Protein Misfolding Disorders Laboratory, George and Cynthia Mitchell Center for Neurodegenerative diseases, Departments of Neurology, Neuroscience & Cell Biology and Biochemistry & Molecular Biology, University of Texas Medical Branch, 301 University Boulevard, Galveston, Texas, 77555-0646, USA 2 Facultad de Ciencias, Universidad de Chile, Santiago, Chile #To whom correspondence should be addressed at Email: The publisher's final edited version of this article is available at Biochim Biophys Acta. See other articles in PMC that cite the published article.


Prions are unconventional infectious agents responsible for transmissible spongiform encephalopathies. Compelling evidences indicate that prions are composed exclusively by a misfolded form of the prion protein (PrPSc) that replicates in the absence of nucleic acids. One of the most challenging problems for the prion hypothesis is the existence of different strains of the infectious agent. Prion strains have been characterized in most of the species. Biochemical characteristics of PrPSc used to identify each strain include glycosylation profile, electrophoretic mobility, protease resistance, and sedimentation. In vivo, prion strains can be differentiated by the clinical signs, incubation period after inoculation and the vacuolation lesion profiles in the brain of affected animals. Sources of prion strain diversity are the inherent conformational flexibility of the prion protein, the presence of PrP polymorphisms and inter-species transmissibility. The existence of the strain phenomenon is not only a scientific challenge, but it also represents a serious risk for public health. The dynamic nature and inter-relations between strains and the potential for the generation of a very large number of new prion strains is the perfect recipe for the emergence of extremely dangerous new infectious agents.


BSE has not only been transmitted to humans. The extensive use of cow-derived material for feeding other animals led to the generation of new diseases in exotic felines such as tiger and cheetah, non human primates, and domestic cats [52,57-60]. As it was mentioned before, the transmission of BSE into these different species could create many new prion strains, each one of them with particular biological and biochemical characteristics and thus a potentially new hazard for human health. Successful transmission of BSE in pigs has been described [61,62] and also in transgenic mice expressing pig PrP (PoPrP) [63]. Porcine derivates are widely consumed and the hypothetic case of "mad pigs" could increase the events of zoonotic transmission of prions to humans. Fortunately, transmission of BSE to pigs is possible only in very drastic conditions, not likely to be occurring naturally [62,63]. More frightening is perhaps the possibility that BSE has been passed into sheep and goats. Studies have already shown that this transmission is possible and actually relatively easy and worrisomely produces a disease clinically similar to scrapie [64]. The cattle origin of this new scrapie makes possible that the new strain may be transmissible to humans. Transmission experiments of BSE infected sheep brain homogenate into human transgenic animal models are currently ongoing in several laboratories. It is very important to note that all materials generated by transmission of BSE in experimental and natural cases show similar biochemical behavior compared to the original inoculum [65], suggesting that all these new generated infectious agents could potentially be hazardous for humans. The origin of BSE is still a mystery. Abundant evidence supports the hypothesis that BSE was produced by cattle feeding with scrapie derivated material [66,67], indicating that bovine PrPSc might be a "conformational intermediary" between ovine PrPSc and human PrPC.

There is currently no mean to predict which will be the conformation of a newly generated strain and how this new PrPSc conformation could affect other species. One interesting new prion disease is CWD, a disease affecting farm and wild species of cervids [68,69]. The origin of CWD and its potential to transmit to humans are currently unknown. This is worrisome, considering that CWD has became endemic in some parts of USA and the number of cases continues to increase [69]. It is presumed that a large number of hunters in the US have been in contact or consumed CWD-infected meat [70]. CWD transmissibility studies have been performed in many species in order to predict how this disease could be spread by consumption of CWD meat [71-73]. In these studies, a special attention has been done to scavenging animals [74], which are presumed to be exposed to high concentration of cervid prions, resulting in the putative generation of many new forms of TSEs. Fortunately negative results were obtained in one experiment done in raccoons infected with CWD [74]. Transmission of CWD to humans cannot be ruled out at present and a similar infective episode to BSE involving CWD could result in catastrophic events, spreading the disease in a very dangerous way through the human population. No clinical evidence linking CWD exposed humans and CJD patients have been found [70], but experimental inoculation of CWD prions into squirrel monkeys propagated the disease [71]. It is important to mention that the species barrier between humans and cervids appears to be greater than with cattle, as judged by experiments with transgenic mice models [75]. Finally, it is important to be aware about CWD transmissibility to other species in which a "conformational intermediary" could be formed, facilitating human infection.


VI. Unique features of prion strains

The biological and infectious characteristics of prions are dramatically different to the conventional infectious agents. These differences are manifested in the prion strains phenomenon in unique and unprecedented features, such as for example strain adaptation and memory, the coexistence and competition of prion strains, among others. In this section, some of these interesting phenomena will be briefly described.

Adaptation of Prion strains

Interspecies transmission of prions could result in the emergence of more than one variety of infectious material. All new collected infectious agents could present particular strain characteristics. That is the case of DY and HY prion strains generation [13,16]. When interspecies transmission of prions occurs, serial passages in the new host are needed in order to stabilize the characteristics of new generated infectious material. In the case of TME transmission in hamsters, at least four serial passages in the new species were required for stabilization [13]. The first passage was characterized by long incubation periods and a dominance of a 19 KDa fragment when newly obtained PrPSc was analyzed after PK digestion. In the three first passages, clinical symptoms were not characteristic of the hamster-adapted HY or DY TME strains. This phenotype was attributed to the combination effects of both strains replicating simultaneously. Thereafter, each of the strains was stabilized in some of the animals and once they are adapted and stabilized, they can be serially propagated in vivo and the characteristics are maintained. It is accepted that both strains present differential conversion kinetics in vitro, with DY being the slowest and HY the fastest [124]. For this reason, in order to select efficiently this prion strain, limit dilutions must be performed [13]. In that way, the most abundant and less convertible DY is favored against the less abundant but fastest HY strain.

Co-existence of prion strains

Related to the above, it has been shown that two or more prion strains can co-exist in natural cases of TSE. Co-existence of prion strains has been found in sporadic cases of CJD [113, 125]. Analyses of several sCJD tissue showed that different biochemical profiles of PrPSc could be found in different brain areas from the same patient [113]. Co-existence of prion strains was mainly observed in patient heterozygous for codon 129 [113]. As many as 50% of these patients present different types of PrPSc in their brains, whereas 9% of MM patients were positive for co-existence of strains. On the other hand, more than one PrPSc type was not observed in VV patients [113].

The biochemical and structural properties of the protein seem to be the major cause of this differential distribution. This observation may explain why sCJD is so heterogeneous in terms of clinical manifestation [34,126,127]. In a recent publication by Bishop et al. [107], vCJD infected transgenic mice expressing human PrPC, present changes in their PrPSc and vacuolation patterns in the brain according to their polymorphic classification for codon 129.

Competition of prion strains

In particular experimental conditions, some prion strains can extend their specific incubation period when co-infected with another strain. Long incubation period prions increase the incubation period of "faster" prions. This phenomenon of "competition of prion strains" has been observed in mice and hamster. In mice, competition between 22A and 22C strains was reported in 1975 by Dickinson et al. [128]. In this study, RIII mice (homozygous for sincs7 allele) were used. 22A and 22C showed long and short incubation period (550 and 230 days), respectively. When 22C strain was intraperitoneally inoculated 100, 200 and 300 days after intraperitoneal administration of the 22A agent, all three experimental groups resulted in Morales et al. Page 8 Biochim Biophys Acta. Author manuscript; available in PMC 2008 December 9. NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript incubation periods and lesion patterns matching 22A prions, suggesting that 22C prions were degraded or excreted, in animals previously infected by 22A. Similar results were obtained by Kimberlin and Walker in 1985 [129] using a different strain of sincs7 mice. These authors treated mice using 22A and 22C prion strain. Before inoculation, 22A was treated with different chemical and physical agents in order to see if the "competitor" or "blocking" characteristics of 22A were maintained. From all treatments, 12M urea was shown to almost abolish the blocking properties of 22A agent. This information suggests that infective properties of long incubation period agent are strictly necessary in order to increase the incubation period of faster prions.

In hamster, similar observations were reported using DY and HY [130]. DY prion strain was inoculated 30 and 60 days prior intraperitoneal inoculation of HY at three different doses. When incubation periods of HY inoculated control group were compared with the animals inoculated at 60 days with DY, significant differences in the incubation periods were found, especially when HY prions were administrated in a higher dose [130]. On the other hand no differences were observed in the case of intranerve inoculation, revealing that competition phenomenon occurs only when peripheral inoculation is performed. These results are surprising considering the fact that DY was reported not to be infectious when intraperitoneally inoculated in hamsters [130]. This data suggest that replication of DY is occurring in peripheral tissues but is not able to reach the central nervous system.

In general, the principal variables that need to be observed for a successful competition are the route of infection, the interval between injections and the particular strains and doses of agent used. Prolongation of incubation periods in TSE are therapeutically beneficial and several strategies are under development to reach this aim, including antibodies, beta-sheet breakers, and other chemical agents [131-133]. The experimental evidence described above suggests that prions could be potentially useful for this purpose. In order to prevent spread of prion disease in cattle or humans, prion strains with incubation periods longer than species' lifespan could be used to slowdown the replication of BSE or vCJD prions.

VII. Concluding Remarks

The existence of different strains of an infectious agent composed exclusively of a protein has been one of the most puzzling issues in the prion field. If is already difficult to understand how a protein can adopt two stable and different folded structures and that one of them can transform the other one into itself, it is unthinkable that the misfolded form can in turn adopt multiple conformations with distinct properties. Yet, compelling scientific evidence support the idea that PrP can adopt numerous folding patterns that can faithfully replicate and produce different diseases. The existence of the strain phenomenon is not only a scientific challenge, but it also represents a serious risk for public health. The dynamic nature and inter-relations between strains and the potential for the generation of many new prion strains depending on the polymorphisms and the crossing of species barrier is the perfect recipe for the emergence of extremely dangerous new infectious agents. Although, substantial progress has been made in understanding the prion strains phenomenon, there are many open questions that need urgent answers, including: what are the structural basis of prion strains?; how are the phenomena of strain adaptation and memory enciphered in the conformation of the prion agent?; to what species can a given prion strain be transmissible?; what other cellular factors control the origin and properties of prion strains?. ...SNIP...END

Friday, December 12, 2008

The prion strain phenomenon: Molecular basis and unprecedented features


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