State and Provincial Updates
The following press release was issued by the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) on October 20, 2017 (https://datcp.wi.gov/Pages/News_Media/WaupacaCWDPositive20171020.aspx):
CWD-positive white-tailed deer found on Waupaca County hunting ranch
MADISON – Two white-tailed deer from a hunting ranch in Waupaca County have tested positive for chronic wasting disease (CWD), Wisconsin State Veterinarian Dr. Paul McGraw announced today. The National Veterinary Services Laboratory in Ames, Iowa, confirmed the test results.
The bucks, ages 2 and 3 years, were part of the 40 deer reported to be on the 84-acre ranch, according to the owner’s most recent registration. One buck was hunter killed and the other was euthanized due to an injury. Neither animal showed clinical signs of CWD. Both were sampled in accordance with Wisconsin Department of Agriculture, Trade and Consumer Protection’s (DATCP’s) rules, which require testing of farm-raised deer and elk when they die or are killed.
McGraw quarantined three properties under the same ownership, which allows movement of deer between ranches and to slaughter, but stops movement of live deer to anywhere else. The business will be allowed to conduct hunts on the quarantined ranches because properly handled dead animals leaving the premises do not pose a disease risk.
The DATCP Animal Health Division will initiate an investigation that examines the animal’s history and trace movements of deer to determine whether other herds may have been exposed to the CWD test-positive deer.
The following press release was issued by the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) on October 3, 2017 (https://datcp.wi.gov/Pages/News_Media/20171003CWDPosShawano.aspx):
CWD-positive white-tailed deer found on Shawano County hunting ranch
MADISON – A white-tailed deer from a hunting ranch in Shawano County has tested positive for chronic wasting disease (CWD), Wisconsin State Veterinarian Dr. Paul McGraw announced today. The National Veterinary Services Laboratory in Ames, Iowa, confirmed the test results.
The 3-year-old Shawano County buck was one of about 245 deer reported to be on the 481-acre ranch, according to the owner’s most recent registration. The deer was born on a Wilderness Game Farm, Inc. breeding facility in May 2014 and transferred to the hunting ranch in Shawano County in September 2015.
Samples were taken from the deer in accordance with Wisconsin Department of Agriculture, Trade and Consumer Protection’s (DATCP’s) rules, which require testing of farm-raised deer and elk when they die or are killed.
McGraw quarantined the Shawano County herd and its related breeding farm in Waupaca County, which allows movement of deer from the breeding farm to the ranch and to slaughter, but stops movement of live deer to anywhere else. The business will be allowed to conduct hunts on the quarantined ranch because properly handled dead animals leaving the premises do not pose a disease risk.
The DATCP Animal Health Division will initiate an investigation that examines the animal’s history and trace movements of deer onto and off the property to determine whether other herds may have been exposed to the CWD test-positive deer.
Additional information regarding the Farm-Raised Deer Program in Wisconsin, including CWD requirements, is available from DATCP at: https://datcp.wi.gov/Pages/Programs_Services/FarmRaisedDeer.aspx.
The following press release was issued by the Michigan Department of Natural resources on October 24, 2017 (http://www.michigan.gov/dnr/0,4570,7-153-10366_54559_10402-450578–,00.html):
Another Montcalm County deer suspected to have CWD
The Michigan Department of Natural Resources announced today that a second hunter-harvested deer in Montcalm County is suspected positive for chronic wasting disease. A sample has been sent to the U.S. Department of Agriculture’s National Veterinary Services Laboratory in Ames, Iowa, for confirmation. If confirmed positive, the 1.5-year-old buck, harvested in Sidney Township, would be the 11th free-ranging deer in Michigan found to have CWD.
“The fact that we already have another positive deer within Montcalm County is of major concern,” said Dr. Kelly Straka, DNR state wildlife veterinarian. “We strongly recommend hunters who harvest deer in Montcalm County have their deer tested. Deer with CWD can look perfectly healthy even though they are infected.”
To date, there have been no reported cases of CWD infection in humans. However, as a precaution, the U.S. Centers for Disease Control and the World Health Organization recommend that infected animals not be consumed as food by either humans or domestic animals.
Since May 2015 when the first CWD deer was found, the DNR has tested more than 15,000 deer. Thus far, 10 cases of CWD have been confirmed in free-ranging white-tailed deer from Clinton, Ingham and Montcalm counties.
As additional deer have tested positive for CWD within Michigan, the DNR has put specific regulations in place. This deer was harvested in the Montcalm-Kent Core CWD Area, which includes Maple Valley, Pine, Douglass, Montcalm, Sidney, Eureka, and Fairplain townships in Montcalm County; and Spencer and Oakfield townships in Kent County. Starting Nov. 15, this nine-township area will have mandatory deer check.
Chronic wasting disease is a fatal neurological disease that affects white-tailed deer, mule deer, elk and moose. It is caused by the transmission of infectious, self-multiplying proteins (prions) contained in saliva and other body fluids of infected animals. Susceptible animals can acquire CWD by direct exposure to these fluids, from environments contaminated with these fluids, or from the carcass of a diseased animal.
Some CWD-infected animals will display abnormal behaviors, progressive weight loss and physical debilitation; however, deer can be infected for many years without showing internal or external symptoms. There is no cure; once a deer is infected with CWD, it will die.
To learn more about CWD, visit mi.gov/cwd.
The following press release was issued by the Texas Animal Health Commission on October 18, 2017 (http://www.tahc.state.tx.us/news/2017/2017-10-18_CWDElk.pdf):
Medina County Elk Tests Positive for Chronic Wasting Disease
Austin, TX – Texas Animal Health Commission (TAHC) officials have confirmed Chronic Wasting Disease (CWD) in an elk located within the South-Central Texas CWD Zone. The elk was harvested on a high-fenced premises with common management as a property where white- tailed deer were previously confirmed to have CWD.
This case was detected as part of the ranch’s herd management plan, which was developed by TAHC to assess the ranch’s risk of CWD.
CWD has been found in free-ranging elk across the United States, including New Mexico and Colorado. This is the second known elk in Texas to test positive for CWD. The first CWD positive elk in Texas was a free-ranging elk harvested in Dallam County on December 6, 2016.
Due to CWD being found in white-tailed deer, mule deer and elk, TAHC established movement and surveillance requirements for exotics in CWD Zones and statewide on May 30, 2017. Statewide surveillance requires all eligible mortalities of exotic CWD susceptible species be tested until such time that three animals are tested. Please note that for CWD Surveillance and Containment Zones, all exotic CWD susceptible species hunter harvested must be tested. To learn more about the TAHC exotic CWD susceptible species statewide surveillance and movement requirements, visit http://www.tahc.texas.gov/news/2017/2017-05- 30_CommissionMeeting.pdf. For more information about CWD regulations within CWD Zones, visit https://tpwd.texas.gov/publications/pwdpubs/media/pwd_bk_w7000_1942.pdf.
CWD was first recognized in 1967 in captive mule deer in Colorado. The first case of CWD in Texas was discovered in 2012 in free-ranging mule deer in an isolated area of far West Texas. The disease has since been detected in a total of 15 free-ranging mule deer, 1 free-ranging elk, this elk located on a high-fenced property, 1 free-ranging white-tailed deer, and in 5 white-tailed deer breeding operations located in Medina/Uvalde and Lavaca counties. For a full list of CWD positives in Texas, visit https://tpwd.texas.gov/huntwild/wild/diseases/cwd/tracking/#texasCWD.
CWD is a progressive, fatal disease of cervids that commonly results in altered behavior as a result of microscopic changes made to the brain of affected animals. An animal may carry the disease for years without outward indication, but in the latter stages, signs may include listlessness, lowering of the head, weight loss, repetitive walking in set patterns, and a lack of responsiveness. CWD is not known to affect humans, however, recent studies suggest there may be a risk to non-human primates that consume CWD infected meat, therefore, the U.S. Centers for Disease Control and the World Health Organization recommend not to consume meat from infected animals.
For more information about CWD please visit http://www.tahc.texas.gov/animal_health/cwd/cwd.html and http://tpwd.texas.gov/huntwild/wild/diseases/cwd/.
The following press release was issued by the Texas Parks and Wildlife Department on May 15, 2017 (http://tpwd.texas.gov/newsmedia/releases/?req=20170515a):
New CWD Case Discovered at Fifth Captive Deer Breeding Facility
Austin – A case of chronic wasting disease (CWD) has been validated in a captive white-tailed deer at another breeding facility in Medina County. The Texas Parks and Wildlife Department (TPWD) and Texas Animal Health Commission (TAHC) are conducting an epidemiological investigation into this new case.
The latest finding is from a 3 ½ – year-old buck that underwent a live test rectal biopsy for CWD conducted in March by the deer breeder. Tissue samples revealed the presence of CWD prions during testing at the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) in College Station. TAHC and TPWD were notified by TVMDL of a suspect positive on May 1. The samples were then submitted to the National Veterinary Services Laboratory in Ames, Iowa, which validated the suspect findings on May 9.
TAHC and TPWD are working with the breeder to develop a CWD herd plan.
The facility is in the immediate vicinity of two positive deer breeding facilities/release sites and one low fence ranch where CWD was detected in a free-ranging deer. The latest discovery marks the 50th confirmed positive case of CWD in Texas since 2012. 5
CWD among cervids is a progressive, fatal disease that commonly results in altered behavior as a result of microscopic changes made to the brain of affected animals. An animal may carry the disease for years without outward indication, but in the latter stages, signs may include listlessness, lowering of the head, weight loss, repetitive walking in set patterns and a lack of responsiveness. To date there is no evidence that CWD poses a risk to humans or non-cervids. However, as a precaution, the U.S. Centers for Disease Control and the World Health Organization recommend not to consume meat from infected animals.
More information on CWD can be found on TPWD’s website, http://www.tpwd.texas.gov/CWD or at the Chronic Wasting Disease Alliance website, http://www.cwd-info.org .
More information about the TAHC CWD program may be found at http://www.tahc.state.tx.us/animal_health/cwd/cwd.html.
The Pennsylvania Department of Agriculture issues the following press release on August 11, 2017 (http://www.media.pa.gov/pages/Agriculture_details.aspx?newsid=579):
Bedford County Captive Deer Herd Tests Positive for Chronic Wasting Disease
Harrisburg, PA – The Pennsylvania Department of Agriculture today announced that 27 deer from a Bedford County deer farm have tested positive for Chronic Wasting Disease, or CWD. The department quarantined the herd on February 16, 2017, after a white-tailed deer on the farm died. The deer subsequently tested positive for the disease.
Deer in the quarantined herd of 215 showed no signs of illness. To prevent further spread of the disease, officials from the U.S. Department of Agriculture Veterinary Services, USDA Wildlife Services and the Pennsylvania Department of Agriculture depopulated, or euthanized, the herd on June 20, 2017. USDA provided financial compensation to the farm owner for the loss of the herd.
“We are working directly with captive-deer herd managers to educate them on risk factors and to do whatever possible to safeguard their herds,” State Veterinarian Dr. David Wolfgang said. “Increased surveillance both in and outside fences is paramount, along with employing management strategies, such as uniformly restricting movement of high-risk parts, managing the density and age of captive herds, and considering secondary barriers to prevent direct contact between captive and wild deer.”
The National Veterinary Services Laboratory in Ames, Iowa conducted the testing and reported results to the department and USDA on August 7, 2017. In addition, research samples were collected and submitted to the USDA Cervid Herd Health Team for additional testing to better understand the disease and to help validate live-animal testing methods in the future. Currently, the only accurate test for CWD is post-mortem testing of the brainstem and lymph nodes.
According to the Centers for Disease Control and Prevention, there is no strong evidence that humans or livestock can contract Chronic Wasting Disease.
The disease attacks the brains of infected deer, elk and moose, producing small lesions that eventually result in death. Animals can get the disease through direct contact with saliva, feces and urine from an infected animal.
Clinical signs include weight loss, excessive salivation, increased drinking and urination, and abnormal behavior like stumbling, trembling and depression. Infected deer and elk also may allow unusually close approach by humans or natural predators. The disease is fatal and there is no known treatment or vaccine.
The first cases of CWD in Pennsylvania were detected when two Adams County deer tested positive for CWD in 2012. Since then, 40 captive deer and 60 wild deer have tested positive in the state. Surveillance for the disease has been ongoing in Pennsylvania since 1998.
The department coordinates a mandatory surveillance program for more than 21,000 captive deer on 1,000 breeding farms, hobby farms and hunting preserves. Prior to this herd, 13 captive deer had tested positive since 2012, with three positive tests earlier this year.
For more information, visit agriculture.pa.gov and search “Chronic Wasting Disease.”
The following press release was issued by the Minnesota Board of Animal Health on May 17, 2017 (https://content.govdelivery.com/accounts/MNBAH/bulletins/19b39dd):
Four more farmed white-tailed deer test positive for Chronic Wasting Disease
– Part of disease tracing effort reaching back to 2016 Crow Wing County case
St. Paul – In late April, the Board of Animal Health and United States Department of Agriculture euthanized a quarantined herd of 14 white-tailed deer in Meeker County. Samples collected from the animals were tested at the USDA’s National Veterinary Services Laboratory in Ames, Iowa and four deer were confirmed CWD positive on May 15. This herd was part of an investigation initiated with a CWD infected farmed deer herd found in Crow Wing County late last year.
The Board shared the test results with the Minnesota Department of Natural Resources, which responds to and manages CWD in wild deer. The Board works with the USDA as it investigates and regulates CWD in farmed deer. The owner agreed to euthanize the animals and test them for CWD as part of a herd plan developed between the USDA, the Board and the owner after finding a trace animal in the herd was positive for CWD in January of this year.
The herd plan also includes tracing animal movements into and out of this herd within the last five years. This tracing revealed two of the four CWD positive animals came from a Wright County deer farm as fawns in 2014. The Wright County farm has also been placed under quarantine as of May 15. 7
“This emphasizes the need for a strong CWD surveillance program in our captive deer and elk. Although these animals appeared healthy, they were infected with CWD and would have continued to spread the disease if they remained alive. CWD testing all deer and elk that die or are killed on a producer’s property is critical to the program,” said Board Assistant Director, Dr. Linda Glaser. “We quarantined the Wright County herd after discovering two of the four CWD positives originated there, but that herd is not considered infected. Herd movements are restricted, and the herd will be closely monitored until 2019.”
The Meeker County farm is empty and remains quarantined for all deer and elk species, and fences remain in place to keep wild deer off of the site. The next step is to clean and disinfect as much of the herd enclosures as possible. When that is complete, the property will remain quarantined for a period of five years.
CWD is a disease of deer and elk caused by an abnormally shaped protein, a prion, which can damage brain and nerve tissue. There is no danger to other animal species. The disease is most likely transmitted when infected deer and elk shed prions in saliva, feces, urine, and other fluids or tissues. The disease is always fatal, and there are no known treatments or vaccines. CWD is not known to affect humans, though consuming infected meat is not advised.
The Wyoming Game and Fish Department issued the following press release on September 25, 2017 (https://wgfd.wyo.gov/News/Information-on-chronic-wasting-disease-for-hunters):
Information on chronic wasting disease for hunters available from Game and Fish and human health agencies
– CWD also found in new deer hunt area south of Gillette
Cheyenne – The Wyoming Game and Fish Department is reminding hunters that chronic wasting disease (CWD), a fatal disease caused by prions that impacts deer, elk, and moose has been documented across much of Wyoming. A prion is a protein that can cause a disease where normal proteins in the brain fold abnormally. More CWD information is available online from the Game and Fish and Centers for Disease Control and Prevention (CDC). For several years Game and Fish has been asking hunters to help with monitoring of the disease by getting their harvested animals tested. Game and Fish also shares the CDC recommendation that hunters should strongly consider getting their animals tested if they are harvested in a known CWD endemic area. “Game and Fish really appreciates all hunters who submit samples and we want the public to know what human health agencies have to say about the disease, including recommendations on not consuming meat from a CWD-positive animal. The public plays a very important role in taking on CWD,” said Scott Edberg, deputy chief of the Wildlife Division. “We, in turn, try to provide current information to the public including maps of the CWD endemic areas on our website.” Because CWD has moved into Wyoming’s western areas, Game and Fish puts extra focus on that area and asks hunters to bring in their harvested deer, elk or moose for sampling to get a better understanding of CWD presence and distribution by species and prevalence rates. To submit a sample, hunters have several options:
Game and Fish check stations – these are established throughout the state during big game seasons.
In the field – when in contact with a game warden, wildlife biologist, or other employee who are collecting CWD samples.
Wyoming State Veterinary Lab – Hunters wishing to have their animal tested outside the Department’s monitoring program may contact the Wyoming State Veterinary Lab in Laramie for details and cost. The telephone number is (307) 766‐9925.
Select meat processors and taxidermists – in certain locations during opening day or few days after seasons open, a Game and Fish employee is present at some of these businesses. Availability varies greatly across the state.
Game and Fish regional offices – in many cases if a hunter stops at a Game and Fish office to get a CWD sample collected, the hunter may have to leave the head at the office until such time a warden or biologist is available to take the sample as they are in the field a majority of the hunting season. But, stop by to check or call first to see what arrangements can be made.
Hunters can collect a CWD sample themselves and bring it to a Game and Fish region office. Watch a video of how to collect this sample. To submit, hunters will need to bring their hunting license and know the location where the animal was harvested.
Game and Fish cautions that the testing program is not focused on ensuring meat quality. Game and Fish supports the CDC recommendations that the public not eat any animal that is obviously ill or tests positive for CWD. Game and Fish also urges hunters to wear rubber or latex gloves as a general precaution against all diseases when field dressing an animal. CWD has now been in found in Deer Hunt Area 19, which is southwest of Gillette. The local warden removed a buck mule deer and had it sampled and it came back positive for CWD. “There are some tips that Game and Fish offers on the best ways to make sure hunters submit a usable CWD sample,” Edberg said. “We need need the unfrozen and unrotten – fresher the better – head of any deer, elk or moose with the upper portion of the neck attached. The sampling process takes about 5-10 minutes.” Game and Fish will also ask for the hunt area and a specific location where the harvest occurred. If a sample submitted to Game and Fish’s CWD surveillance program tests positive and adequate contact information is provided, the hunter will be notified of the positive test result. Hunters who participate in Game and Fish’s CWD surveillance program by providing deer, elk, or moose tissue samples and provide adequate information, can obtain their test results at: https://wgfd.wyo.gov/services/education/cwd/surveillance/frmlookup.aspx.
For more information about CWD in Wyoming, visit the Game and Fish website. For more information about CWD in North America, visit the CWD Alliance website.
Alberta Environment and Parks issued the following surveillance update on April 20, 2017 (http://aep.alberta.ca/fish-wildlife/wildlife-diseases/chronic-wasting-disease/cwd-updates/default.aspx):
Chronic Wasting Disease (CWD) Surveillance Update: 2016/17 Final
We have completed the heads received to date from the 2016/17 hunting seasons. A total of 5112 heads were tested since September 1, 2016, and we detected CWD in 179 animals (3.5%; up from 2.4% in 2015/16). The positives included 178 deer (154 mule deer, 23 white-tail, 1 unknown deer; 136 males, 41 females, 1 unknown gender) and 1 male elk. As in previous years the majority of cases (119 of 179; 66%) were mule deer bucks.
Also as in previous years, species- and gender-specific differences are apparent in the surveillance data. In the 4944 heads that were suitable for determining disease status, CWD was detected in:
5.4% of 2833 mule deer
1.5% of 1494 white-tailed deer
0.2% of 431 elk (primarily from CFB Suffield)
0 of 176 moose (primarily from CFB Wainwright)
In the 4312 deer for which gender/sex was reported, CWD was detected in:
8.1% of 1473 male mule deer
2.6% of 1349 female mule deer
1.7% of 1071 male whitetails
1.3% of 473 female whitetails
The disease continues to expand further westward into central Alberta. In the 2016/17 surveillance sample, CWD was again detected beyond the known range in the province (further up the Red Deer River in Wildlife Management Unit (WMU) 158, in WMU 230 in the Battle River watershed, in WMU 254 in the Vermilion River watershed).
These units are adjacent to previous cases and indicate further geographic spread of CWD along major waterways. However, the finding of CWD in a white-tailed deer in WMU 250 northeast of Fort Saskatchewan is a significant westward extension of the known occurrence in the North Saskatchewan River watershed.
We also detected CWD in a bull elk from WMU 732 (Canadian Forces Base Suffield). Since 2012, we tested 1973 elk from WMU 732 and this is the first one found to have CWD (0.05%). 10
The disease is well established in mule deer and white-tailed deer in areas outside the military base along the Red Deer and South Saskatchewan rivers.
The complete Alberta surveillance update, including graphics, is available at: http://aep.alberta.ca/fish-wildlife/wildlife-diseases/chronic-wasting-disease/cwd-updates/default.aspx.
Endemic chronic wasting disease causes mule deer population decline in Wyoming
Melia T. DeVivo, David R. Edmunds, Matthew J. Kauffman, Brant A. Schumaker, Justin Binfet, Terry J. Kreeger, Bryan J. Richards, Hermann M. Schätzl, Todd E. Cornish
PLoS ONE12(10): e0186512. https://doi.org/10.1371/journal.pone.0186512
Chronic wasting disease (CWD) is a fatal transmissible spongiform encephalopathy affecting white-tailed deer (Odocoileus virginianus), mule deer (Odocoileus hemionus), Rocky Mountain elk (Cervus elaphus nelsoni), and moose (Alces alces shirasi) in North America. In southeastern Wyoming average annual CWD prevalence in mule deer exceeds 20% and appears to contribute to regional population declines. We determined the effect of CWD on mule deer demography using age-specific, female-only, CWD transition matrix models to estimate the population growth rate (λ. Mule deer were captured from 2010–2014 in southern Converse County Wyoming, USA. Captured adult (≥1.5 years old) deer were tested ante-mortem for CWD using tonsil biopsies and monitored using radio telemetry. Mean annual survival rates of CWD-negative and CWD-positive deer were 0.76 and 0.32, respectively. Pregnancy and fawn recruitment were not observed to be influenced by CWD. We estimated λ= 0.79, indicating an annual population decline of 21% under current CWD prevalence levels. A model derived from the demography of only CWD-negative individuals yielded; λ= 1.00, indicating a stable population if CWD were absent. These findings support CWD as a significant contributor to mule deer population decline. Chronic wasting disease is difficult or impossible to eradicate with current tools, given significant environmental contamination, and at present our best recommendation for control of this disease is to minimize spread to new areas and naïve cervid populations.
Experimental transmission of the Chronic Wasting Disease agent to swine after oral or intracranial inoculation
- Jo Moore, M. Heather West Greenlee, Naveen Kondru, Sireesha Manne, Jodi D. Smith, Robert A. Kunkle, Anumantha Kanthasamy, Justin J. Greenlee
Journal of Virology 91:e00926-17. https://doi.org/10.1128/JVI.00926-17
Chronic wasting disease (CWD) is a naturally occurring, fatal neurodegenerative disease of cervids. The potential for swine to serve as hosts for the agent of CWD is unknown. The purpose of this study was to investigate the susceptibility of swine to the CWD agent following experimental oral or intracranial inoculation. Crossbred piglets were assigned to three groups, intracranially inoculated (n = 20), orally inoculated (n = 19), and noninoculated (n = 9). At approximately the age at which commercial pigs reach market weight, half of the pigs in each group were culled (“market weight” groups). The remaining pigs (“aged” groups) were allowed to incubate for up to 73 months postinoculation (mpi). Tissues collected at necropsy were examined for disease-associated prion protein (PrPSc) by Western blotting (WB), antigen capture enzyme immunoassay (EIA), immunohistochemistry (IHC), and in vitro real-time quaking-induced conversion (RT-QuIC). Brain samples from selected pigs were also bioassayed in mice expressing porcine prion protein. Four intracranially inoculated aged pigs and one orally inoculated aged pig were positive by EIA, IHC, and/or WB. By RT-QuIC, PrPSc was detected in lymphoid and/or brain tissue from one or more pigs in each inoculated group. The bioassay was positive in four out of five pigs assayed. This study demonstrates that pigs can support low-level amplification of CWD prions, although the species barrier to CWD infection is relatively high. However, detection of infectivity in orally inoculated pigs with a mouse bioassay raises the possibility that naturally exposed pigs could act as a reservoir of CWD infectivity.
Pathways of prion spread during early Chronic Wasting Disease in deer
Clare E. Hoover, Kristen A. Davenport, Davin M. Henderson, Nathaniel D. Denkers, Candace K. Mathiason, Claudio Soto, Mark D. Zabel, Edward A. Hoover
Journal of Virology 91:e00077-17. https://doi.org/10.1128/JVI.00077-17
Among prion infections, two scenarios of prion spread are generally observed: (i) early lymphoid tissue replication or (ii) direct neuroinvasion without substantial antecedent lymphoid amplification. In nature, cervids are infected with chronic wasting disease (CWD) prions by oral and nasal mucosal exposure, and studies of early CWD pathogenesis have implicated pharyngeal lymphoid tissue as the earliest sites of prion accumulation. However, knowledge of chronological events in prion spread during early infection remains incomplete. To investigate this knowledge gap in early CWD pathogenesis, we exposed white-tailed deer to CWD prions by mucosal routes and performed serial necropsies to assess PrPCWD tissue distribution by real-time quaking-induced conversion (RT-QuIC) and tyramide signal amplification immunohistochemistry (TSA-IHC). Although PrPCWD was not detected by either method in the initial days (1 and 3) postexposure, we observed PrPCWD seeding activity and follicular immunoreactivity in oropharyngeal lymphoid tissues at 1 and 2 months postexposure (MPE). At 3 MPE, PrPCWD replication had expanded to all systemic lymphoid tissues. By 4 MPE, the PrPCWD burden in all lymphoid tissues had increased and approached levels observed in terminal disease, yet there was no evidence of nervous system invasion. These results indicate the first site of CWD prion entry is in the oropharynx, and the initial phase of prion amplification occurs in the oropharyngeal lymphoid tissues followed by rapid dissemination to systemic lymphoid tissues. This lymphoid replication phase appears to precede neuroinvasion.
Evolution of diagnostic tests for Chronic Wasting Disease, a naturally occurring prion disease of cervids
Nicholas J. Haley and Jürgen A. Richt
Pathogens 2017, 6, 35; doi:10.3390/pathogens6030035
Since chronic wasting disease (CWD) was first identified nearly 50 years ago in a captive mule deer herd in the Rocky Mountains of the United States, it has slowly spread across North America through the natural and anthropogenic movement of cervids and their carcasses. As the endemic areas have expanded, so has the need for rapid, sensitive, and cost effective diagnostic tests—especially those which take advantage of samples collected antemortem. Over the past two decades, strategies have evolved from the recognition of microscopic spongiform pathology and associated immunohistochemical staining of the misfolded prion protein to enzyme-linked immunoassays capable of detecting the abnormal prion conformer in postmortem samples. In a history that parallels the diagnosis of more conventional infectious agents, both qualitative and real-time amplification assays have recently been developed to detect minute quantities of misfolded prions in a range of biological and environmental samples. With these more sensitive and semi-quantitative approaches has come a greater understanding of the pathogenesis and epidemiology of this disease in the native host. Because the molecular pathogenesis of prion protein misfolding is broadly analogous to the misfolding of other pathogenic proteins, including Aβand α-synuclein, efforts are currently underway to apply these in vitro amplification techniques towards the diagnosis of Alzheimer’s disease, Parkinson’s disease, and other proteinopathies. Chronic wasting disease—once a rare disease of Colorado mule deer—now represents one of the most prevalent prion diseases, and should serve as a model for the continued development and implementation of novel diagnostic strategies for protein misfolding disorders in the natural host.