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Chronic wasting disease (CWD), sometimes called zombie deer disease, is a
transmissible spongiform encephalopathy Transmissible spongiform encephalopathies (TSEs) are a group of progressive and fatal conditions that are associated with prions and affect the brain and nervous system of many animals, including humans, cattle, and sheep. According to the most ...
(TSE) affecting
deer Deer or true deer are hoofed ruminant mammals forming the family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, and the fallow deer; and the Capreolinae, including the re ...
. TSEs are a family of diseases thought to be caused by misfolded proteins called
prions Prions are misfolded proteins that have the ability to transmit their misfolded shape onto normal variants of the same protein. They characterize several fatal and transmissible neurodegenerative diseases in humans and many other animals. It i ...
and include similar diseases such as BSE (mad cow disease) in cattle, Creutzfeldt-Jakob disease (CJD) in humans and
scrapie Scrapie () is a fatal, degenerative disease affecting the nervous systems of sheep and goats. It is one of several transmissible spongiform encephalopathies (TSEs), and as such it is thought to be caused by a prion. Scrapie has been known since ...
in sheep. In the United States, CWD affects
mule deer The mule deer (''Odocoileus hemionus'') is a deer indigenous to western North America; it is named for its ears, which are large like those of the mule. Two subspecies of mule deer are grouped into the black-tailed deer. Unlike the related whi ...
,
white-tailed deer The white-tailed deer (''Odocoileus virginianus''), also known as the whitetail or Virginia deer, is a medium-sized deer native to North America, Central America, and South America as far south as Peru and Bolivia. It has also been introduced t ...
,
red deer The red deer (''Cervus elaphus'') is one of the largest deer species. A male red deer is called a stag or hart, and a female is called a hind. The red deer inhabits most of Europe, the Caucasus Mountains region, Anatolia, Iran, and parts of ...
,
sika deer The sika deer (''Cervus nippon''), also known as the Northern spotted deer or the Japanese deer, is a species of deer native to much of East Asia and introduced to other parts of the world. Previously found from northern Vietnam in the south to ...
, elk,
caribou Reindeer (in North American English, known as caribou if wild and ''reindeer'' if domesticated) are deer in the genus ''Rangifer''. For the last few decades, reindeer were assigned to one species, ''Rangifer tarandus'', with about 10 subspe ...
, and
moose The moose (in North America) or elk (in Eurasia) (''Alces alces'') is a member of the New World deer subfamily and is the only species in the genus ''Alces''. It is the largest and heaviest extant species in the deer family. Most adult ma ...
. Natural infection causing CWD affects members of the deer family. Experimental transmission of CWD to other species such as
squirrel monkey Squirrel monkeys are New World monkeys of the genus ''Saimiri''. ''Saimiri'' is the only genus in the subfamily Saimirinae. The name of the genus is of Tupi origin (''sai-mirím'' or ''çai-mbirín'', with ''sai'' meaning 'monkey' and ''mirím'' ...
s and genetically modified mice has been shown. In 1967, CWD was first identified in mule deer at a government research facility in northern
Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of the ...
,
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
. It was initially recognized as a clinical "wasting" syndrome and then in 1978, it was identified more specifically as a TSE disease. Since then, CWD has been found in free-ranging and captive animal populations in 30 US states and four Canadian provinces. In addition, CWD has been found in one Minnesota
red deer The red deer (''Cervus elaphus'') is one of the largest deer species. A male red deer is called a stag or hart, and a female is called a hind. The red deer inhabits most of Europe, the Caucasus Mountains region, Anatolia, Iran, and parts of ...
farm, one wild reindeer herd in Norway (March 2016) as well as in wild moose. Single cases of CWD in moose have been found in Finland (March 2018) and in Sweden (March and May 2019, September 2020). CWD was found in South Korea in some deer imported from Canada. CWD is typified by chronic weight loss and clinical signs compatible with brain lesions, aggravated over time, always leading to death. No relationship is known between CWD and any other TSEs of animals or people. Although reports in the popular press have been made of humans being affected by CWD, by 2004 a study for the
Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georg ...
(CDC) suggested, " re epidemiologic and laboratory studies are needed to monitor the possibility of such transmissions". The epidemiological study further concluded, " a precaution, hunters should avoid eating deer and elk tissues known to harbor the CWD agent (e.g., brain, spinal cord, eyes, spleen, tonsils, lymph nodes) from areas where CWD has been identified".


History

Chronic wasting disease was first discovered by American wildlife veterinarian Beth S. Williams. Williams performed necropsies on deer and elk that had died of an unknown syndrome. She recognized that the brain lesions in these animals were consistent with
transmissible spongiform encephalopathy Transmissible spongiform encephalopathies (TSEs) are a group of progressive and fatal conditions that are associated with prions and affect the brain and nervous system of many animals, including humans, cattle, and sheep. According to the most ...
(TSE). In 1978, she and neuropathologist Stuart Young cowrote the first scientific paper that named the disease and described it as a TSE. In February 2003, the
Centers for Disease Control The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georgi ...
published a report of "Fatal degenerative neurologic illnesses in men who participated in wild game feasts--Wisconsin, 2002". It read in conclusion that "Although no association between (animal) CWD and (the feastors in Wisconsin who happened to have) CJD was found, continued surveillance of both diseases remains important to assess the possible risk for CWD transmission to humans." In September 2003, Hoey pointed out that one of the three patients (the 55 year-old) "presented with a 3-month history of difficulty in writing and unsteadiness of gait, followed by dementia, speech abnormalities and myoclonic jerking. Pathologic examination of the brain at autopsy 3 months later revealed widespread subcortical spongiform lesions consistent with CJD." As of 2013 Patrice Klein the CWD Program Manager at USDA/APHIS rejected the somewhat inconclusive findings of Hoey and stated that no evidence had been found of transmission to humans from deer, nor by eating animals in the deer family, but both channels remain a subject of public health surveillance and research.


Quebec farm outbreak

The MFFP ministry in
Quebec Quebec ( ; )According to the Canadian government, ''Québec'' (with the acute accent) is the official name in Canadian French and ''Quebec'' (without the accent) is the province's official name in Canadian English is one of the thirte ...
practiced 9500 tests in the period between 2007 and autumn 2018 before they detected a seropositive case in September 2018. The September 2018 discovery of CWD on a managed operation in Grenville-sur-la-Rouge Quebec prompted a wholesale slaughter of 3500 animals in two months before the enterprise shut down permanently. The CFIA ordered the cull, as well as the decontamination of of soil in certain places on the operation. Post-discovery, each animal was tested for CWD by the CFIA before it was released onto the market. Other Quebec producers lamented the glut of supply. A 400 km quarantine area was declared, in which all hunting and trapping activities were banned. The government slaughtered hundreds of wild animals over a two-month period. The routine cull for market was between 70 and 100 animals per week. When the producer was forced to close, the weekly slaughter neared 500 animals per week. One year later, 750 wild specimens had been culled in the 45 km-radius "enhanced monitoring area", and none tested positive for CWD. It came to light in August 2019 that prior to 2014 in Canada, all animals on CWD-infected farms were buried or incinerated. Since 2014, however, the CFIA has allowed animals from CWD-infected farms to enter the food chain because there is "no national requirement to have animals tested for the disease". From one CWD-infected herd in Alberta, 131 elk were sold for human consumption. For the fall 2019 hunting season in western Quebec, the provincial ministry relaxed the rules for the annual white-tailed deer (WTD) hunt, in an effort to curb the spread of CWD. Any WTD can be hunted with any weapon in certain municipalities in the
Outaouais Outaouais (, ; also commonly called The Outaouais) is a region of western Quebec, Canada. It includes the city of Gatineau, the municipality of Val-des-Monts and the Papineau region. Geographically, it is located on the north side of the Ottaw ...
valley and the
Laurentides The Laurentides () is a region of Quebec. While it is often called the Laurentians in English, the region includes only part of the Laurentian mountains. It has a total land area of and its population was 589,400 inhabitants as of the 2016 C ...
. The MFFP hopes thereby to receive more samples to test for CWD. The quarantine around Grenville was still in place, and the ministry specifically prohibited (only) the "removal" from the quarantine "enhanced monitoring area" zone of "the head, more specifically any part of the brain, the
eyes Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and con ...
, the retropharyngeal
lymph nodes A lymph node, or lymph gland, is a kidney-shaped organ of the lymphatic system and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocytes that includ ...
and the
tonsils The tonsils are a set of lymphoid organs facing into the aerodigestive tract, which is known as Waldeyer's tonsillar ring and consists of the adenoid tonsil, two tubal tonsils, two palatine tonsils, and the lingual tonsils. These organs play a ...
, any part of the
spinal column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordates ...
, the internal organs (including the
liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it i ...
and the
heart The heart is a muscular Organ (biology), organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as ca ...
), and the
testicles A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testosteron ...
."


Signs and symptoms

Due to CWD taking 18–24 months after initial exposure to onset, most cases of CWD occur in adult animals; the youngest animal to exhibit clinical symptoms of the disease was 15 months. The disease is progressive and always fatal. The first signs are difficulties in movement. The most obvious and consistent clinical sign of CWD is weight loss over time. Behavioral changes also occur in the majority of cases, including decreased interactions with other animals, listlessness, lowering of the head, tremors, repetitive walking in set patterns, and nervousness. Excessive salivation and grinding of the teeth also are observed. Most deer show increased drinking and urination; the increased drinking and salivation may contribute to the spread of the disease. Loss of fear of humans and appearance of confusion are also common. The APHIS summarized it as:


Cause

The cause of CWD (like other TSEs, such as
scrapie Scrapie () is a fatal, degenerative disease affecting the nervous systems of sheep and goats. It is one of several transmissible spongiform encephalopathies (TSEs), and as such it is thought to be caused by a prion. Scrapie has been known since ...
and
bovine spongiform encephalopathy Bovine spongiform encephalopathy (BSE), commonly known as mad cow disease, is an incurable and invariably fatal neurodegenerative disease of cattle. Symptoms include abnormal behavior, trouble walking, and weight loss. Later in the course of t ...
) is a
prion Prions are misfolded proteins that have the ability to transmit their misfolded shape onto normal variants of the same protein. They characterize several fatal and transmissible neurodegenerative diseases in humans and many other animals. It i ...
, a misfolded form of a normal
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
, known as prion protein (PrP), that is most commonly found in the
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all p ...
(CNS) and
peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system of bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside the brai ...
(PNS). The misfolded form has been shown to be capable of converting normally folded prion protein, PrPC ("C" for cellular) into an abnormal form, PrPSc ("Sc" for scrapie), thus leading to a chain reaction. CWD is thought to be transmitted by this mechanism. The abnormality in PrP has its genetic basis in a particular variant of the protein-coding gene ''
PRNP Major prion protein (PrP), is encoded in the human by the ''PRNP'' gene also known as CD230 (cluster of differentiation 230). Expression of the protein is most predominant in the nervous system but occurs in many other tissues throughout the bo ...
'' that is highly conserved among mammals and has been found and sequenced in deer. The build-up of PrPd in the brain is associated with widespread
neurodegeneration A neurodegenerative disease is caused by the progressive loss of structure or function of neurons, in the process known as neurodegeneration. Such neuronal damage may ultimately involve cell death. Neurodegenerative diseases include amyotrophi ...
.USGS National Wildlife Health Cente
Frequently asked questions concerning Chronic Wasting Disease (CWD)
Page last updated May 21, 2013; page accessed April 25, 2016


Genetics

The
allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chrom ...
which encodes
leucine Leucine (symbol Leu or L) is an essential amino acid that is used in the biosynthesis of proteins. Leucine is an α-amino acid, meaning it contains an α- amino group (which is in the protonated −NH3+ form under biological conditions), an α- ...
,
codon The genetic code is the set of rules used by living cells to translate information encoded within genetic material ( DNA or RNA sequences of nucleotide triplets, or codons) into proteins. Translation is accomplished by the ribosome, which links ...
132 in the family of Elks, is either
homozygous Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mo ...
LL, homozygous MM, or
heterozygous Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. ...
ML. Individuals with the first encoding seem to resist clinical signs of CWD, whereas individuals with either of the other two encodings have much shorter incubation periods. In white-tailed deer, polymorphisms at codons 95 (Q->H) and 96 (G->S) dramatically affect CWD progression and prion strain specification. Deer containing the 96S allele have delayed progression to clinical disease onset. When deer with the 95H polymorphism become infected, they select for altered strains of CWD.


Spread

Researchers in July 2019 stated that "with all the research on the malignity of prions, and the permanence of prions in the wider environment, and their resistance to destruction and degradation, it is necessary to reduce the potential sources of exposure to CWD." In fact an
APHIS ''Aphis'' is a genus of insects in the family Aphididae containing at least 600 species of aphids. It includes many notorious agricultural pests, such as the soybean aphid '' Aphis glycines''. Many species of ''Aphis'', such as '' A. coreopsidis ...
scientist observed that, while the longevity of CWD prion is unknown, the
scrapie Scrapie () is a fatal, degenerative disease affecting the nervous systems of sheep and goats. It is one of several transmissible spongiform encephalopathies (TSEs), and as such it is thought to be caused by a prion. Scrapie has been known since ...
prion has been measured to endure for 16 years. The PrPCWD protein is insoluble in all but the strongest solvents, and highly resistant to
digestion Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma. In certain organisms, these smaller substances are absorbed through the small intest ...
by
proteases A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the for ...
. PrPCWD converts the normal protein PrPC into more of itself upon contact, and binds together forming aggregates. Prusiner noted in 2001 that: However, it is noted that , although CWD prions were transmissible within the ''cervidae'' family, CWD was not considered transmissible to humans or to cattle. How the prions that cause CWD spread is unknown, but recent research indicates that prions can be excreted by deer and elk, and are transmitted by eating grass growing in contaminated soil. Animals born in captivity and those born in the wild have been affected with the disease. Transmission of CWD is thought to be lateral (from animal to animal). Maternal transmission may occur, although it appears to be relatively unimportant in maintaining epidemics. An infected deer's saliva is able to spread the CWD prions. Exposure between animals is associated with sharing food and water sources contaminated with CWD prions shed by diseased deer.


Direct

CWD may be directly transmitted by contact with infected animals, their bodily tissues, and their bodily fluids. Spread may result from contact with infected deer regardless of if they are symptomatic. Recent research on Rocky Mountain elk found that with CWD-infected cows, many subclinical, a high rate (80%) of maternal-to-offspring transmission of CWD prions occurred, regardless of gestational period. While not dispositive relative to disease development in the fetus, this does suggest that maternal transmission may be yet another important route of direct CWD transmission. Modern news stories and anecdotal evidence from treating physicians suggest that a human may have contracted Creutzfeldt-Jakob disease via the consumption of squirrel brains infected with CWD.


Experimental transmission

In addition to the cervid species in which CWD is known to naturally occur, black-tailed deer and European red deer have been demonstrated to be naturally susceptible to CWD. Other cervid species, including caribou, are also suspected to be naturally vulnerable to this disease. Many other non-cervid mammalian species have been experimentally infected with CWD, either orally or by intracerebral inoculation. These species include monkeys, sheep, cattle, prairie voles, mice, and ferrets. An experimental case study of oral transmission of CWD to reindeer shows certain reindeer breeds may be susceptible to CWD, while other subpopulations may be protective against CWD in free-ranging populations. None of the reindeer in the study showed symptoms of CWD, potentially signifying resistance to different CWD strains.


Indirect

Environmental transmission has been linked to contact with infected bodily fluids and tissues, as well as contact with contaminated environments. Once in the environment, CWD prions may remain infectious for many years. Thus, decomposition of diseased carcasses, infected "gut piles" from hunters who field dress their cervid harvests, and the urine, saliva, feces, and antler velvet of infected individuals that are deposited in the environment, all have the potential to create infectious environmental reservoirs of CWD. In 2013, researchers at the
National Wildlife Research Center National may refer to: Common uses * Nation or country ** Nationality – a ''national'' is a person who is subject to a nation, regardless of whether the person has full rights as a citizen Places in the United States * National, Maryland, c ...
in
Fort Collins, Colorado Fort Collins is a home rule municipality that is the county seat and the most populous municipality of Larimer County, Colorado, United States. The city population was 169,810 at the 2020 census, an increase of 17.94% since 2010. Fort Collin ...
successfully inoculated white-tailed deer with the misfolded prion via the nasal passage, when the prions were mixed with clay. This was important because the prions had already been shown by 2006 to bind with sandy quartz clay minerals. One avian scavenger, the American crow, was recently evaluated as a potential vector for CWD. As CWD prions remain viable after passing through the bird's digestive tract, crows represent a possible mechanism for the creation of environmental reservoirs of CWD. Additionally, the crows' extensive geographic range presents ample opportunities for them to come in contact with CWD. This, coupled with the population density and longevity of communal roosting sites in both urban and rural locations, suggests that the fecal deposits at roosting sites may represent a CWD environmental reservoir. Conservative estimates for crows' fecal deposits at one winter roosting site for one winter season ranged from 391,552 to 599,032 kg. CWD prions adhere so tightly to soil surface particles that the ground becomes a source of infection and may be a major route of transmission due to frequent ground contact when animals in the deer family graze.


Prevention

By 2012, a voluntary system of control was published by
APHIS ''Aphis'' is a genus of insects in the family Aphididae containing at least 600 species of aphids. It includes many notorious agricultural pests, such as the soybean aphid '' Aphis glycines''. Many species of ''Aphis'', such as '' A. coreopsidis ...
in the US
Federal Register The ''Federal Register'' (FR or sometimes Fed. Reg.) is the official journal of the federal government of the United States that contains government agency rules, proposed rules, and public notices. It is published every weekday, except on fede ...
. It depended on voluntary minimum standards methodology, and herd certification programs to avoid interstate movement of the disease vector. It was based on a risk management framework. As of August 2019, APHIS law in 9 CFR Part 55 - CONTROL OF CHRONIC WASTING DISEASE dealt with this problem. Introduced for the 2019 Minnesota hunting season, a no-cost deer carcass-incineration program was rolled out by Crow Wing County officials hoping to stem the spread of CWD in the region. CWD was found among wild deer in Crow Wing County for the first time in January 2019. The voluntary program encourages both residents and visiting hunters to bring harvested deer carcasses to the county landfill east of Brainerd, Minnesota for incineration and disposal.


Diagnosis

Diagnosis is based on ''post mortem'' examination (
necropsy An autopsy (post-mortem examination, obduction, necropsy, or autopsia cadaverum) is a surgical procedure that consists of a thorough examination of a corpse by dissection to determine the cause, mode, and manner of death or to evaluate any di ...
) and testing; examination of the dead body is not definitive, as many animals die early in the course of the disease and conditions found are nonspecific; general signs of poor health and
aspiration pneumonia Aspiration pneumonia is a type of lung infection that is due to a relatively large amount of material from the stomach or mouth entering the lungs. Signs and symptoms often include fever and cough of relatively rapid onset. Complications may inc ...
, which may be the actual cause of death, are common. On microscopic examination, lesions of CWD in the CNS resemble those of other TSEs. In addition, scientists use
immunohistochemistry Immunohistochemistry (IHC) is the most common application of immunostaining. It involves the process of selectively identifying antigens (proteins) in cells of a tissue section by exploiting the principle of antibodies binding specifically to ant ...
to test
brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...
,
lymph Lymph (from Latin, , meaning "water") is the fluid that flows through the lymphatic system, a system composed of lymph vessels (channels) and intervening lymph nodes whose function, like the venous system, is to return fluid from the tissues ...
, and neuroendocrine tissues for the presence of the abnormal prion protein to diagnose CWD; positive IHC findings in the
obex OBEX (abbreviation of OBject EXchange, also termed IrOBEX) is a communications protocol that facilitates the exchange of binary objects between devices. It is maintained by the Infrared Data Association but has also been adopted by the Bluetooth S ...
is considered the gold standard. Conventional CWD diagnostic strategies and seeded amplification methods for amplifying CWD prions ''in vitro'' include:
immunohistochemistry Immunohistochemistry (IHC) is the most common application of immunostaining. It involves the process of selectively identifying antigens (proteins) in cells of a tissue section by exploiting the principle of antibodies binding specifically to ant ...
(IHC),
western blotting The western blot (sometimes called the protein immunoblot), or western blotting, is a widely used analytical technique in molecular biology and immunogenetics to detect specific proteins in a sample of tissue homogenate or extract. Besides detect ...
(WB), enzyme immunoassay (EIA),
protein misfolding cyclic amplification Protein misfolding cyclic amplification (PMCA) is an amplification technique (conceptually like PCR but not involving nucleotides) to multiply misfolded prions originally developed by Soto and colleagues.Saborio, G.P., Permanne, B. and Soto, C. (20 ...
(PMCA), and real time quaking-induced conversion ( RT-QuIC). Available tests, as of July 2019, at the CFIA were not sensitive enough to detect the prion in specimens from animals younger than a year old. Strategies are being developed to allow for the quantification of prion burden in a tissue, body fluid, or environmental sample. As of 2015, no commercially feasible diagnostic tests could be used on live animals. As early as 2001 an ''antemortem'' test was deemed urgent. Running a
bioassay A bioassay is an analytical method to determine the concentration or potency of a substance by its effect on living animals or plants (''in vivo''), or on living cells or tissues(''in vitro''). A bioassay can be either quantal or quantitative, dir ...
, taking fluids from animals in the deer family suspected of infection and incubating them in transgenic mice that express the cervid prion protein, can be used to determine whether the cervid is infected, but ethical issues exist with this, and it is not scalable. A tonsillar biopsy technique has been a reliable method of testing for CWD in live deer, but it only seems to be effective on mule deer and white-tailed deer, not elk. Biopsies of the rectal mucosa have also been effective at detecting CWD in live mule deer, white-tailed deer, and elk, though detection efficacy may be influenced by numerous factors including animal age, genotype, and disease stage. It is possible for CWD prions to survive sterilization procedures involving an autoclave.


Epidemiology


North America

The disease was first identified in 1967 in a closed herd of captive
mule deer The mule deer (''Odocoileus hemionus'') is a deer indigenous to western North America; it is named for its ears, which are large like those of the mule. Two subspecies of mule deer are grouped into the black-tailed deer. Unlike the related whi ...
in contiguous portions of northeastern Colorado. In 1980, the disease was determined to be a TSE. It was first identified in wild elk and mule deer and
white-tailed deer The white-tailed deer (''Odocoileus virginianus''), also known as the whitetail or Virginia deer, is a medium-sized deer native to North America, Central America, and South America as far south as Peru and Bolivia. It has also been introduced t ...
in the early 1980s in Colorado and Wyoming, and in farmed elk in 1997. The disease did not affect Canada until 1996. In May 2001, CWD was also found in free-ranging deer in the southwestern corner of
Nebraska Nebraska () is a state in the Midwestern region of the United States. It is bordered by South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Kansas to the south; Colorado to the sout ...
(adjacent to Colorado and Wyoming) and later in additional areas in western Nebraska. The limited area of northern Colorado, southern Wyoming, and western Nebraska in which free-ranging deer, moose, and/or elk positive for CWD have been found is referred to as the
endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...
area. The area in 2006 has expanded to six states, including parts of eastern
Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its ...
, southwestern
South Dakota South Dakota (; Sioux: , ) is a U.S. state in the North Central region of the United States. It is also part of the Great Plains. South Dakota is named after the Lakota and Dakota Sioux Native American tribes, who comprise a large po ...
, and northwestern
Kansas Kansas () is a U.S. state, state in the Midwestern United States, Midwestern United States. Its Capital city, capital is Topeka, Kansas, Topeka, and its largest city is Wichita, Kansas, Wichita. Kansas is a landlocked state bordered by Nebras ...
. Also, areas not contiguous (to the endemic area) areas in central Utah and central Nebraska have been found. The limits of the affected areas are not well defined, since the disease is at a low incidence and the amount of sampling may not be adequate to detect it. In 2002, CWD was detected in wild deer in south-central
Wisconsin Wisconsin () is a state in the upper Midwestern United States. Wisconsin is the 25th-largest state by total area and the 20th-most populous. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake M ...
and northern
Illinois Illinois ( ) is a state in the Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolitan areas include, Peoria and Rock ...
and in an isolated area of southern
New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe, New Mexico, Santa Fe , LargestCity = Albuquerque, New Mexico, Albuquerque , LargestMetro = Albuquerque metropolitan area, Tiguex , Offi ...
. In 2005, it was found in wild
white-tailed deer The white-tailed deer (''Odocoileus virginianus''), also known as the whitetail or Virginia deer, is a medium-sized deer native to North America, Central America, and South America as far south as Peru and Bolivia. It has also been introduced t ...
in
New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * '' ...
and in
Hampshire County, West Virginia Hampshire County is a County (United States), county in the U.S. state of West Virginia. As of the 2020 United States census, 2020 census, the population was 23,093. Its county seat is Romney, West Virginia, Romney, West Virginia's oldest town ( ...
. In 2008, the first confirmed case of CWD in
Michigan Michigan () is a state in the Great Lakes region of the upper Midwestern United States. With a population of nearly 10.12 million and an area of nearly , Michigan is the 10th-largest state by population, the 11th-largest by area, and t ...
was discovered in an infected deer on an enclosed deer-breeding facility. It is also found in the Canadian provinces of
Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest T ...
and
Saskatchewan Saskatchewan ( ; ) is a Provinces and territories of Canada, province in Western Canada, western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on t ...
. In February 2011, the
Maryland Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean t ...
Department of Natural Resources reported the first confirmed case of the disease in that state. The affected animal was a white-tailed deer killed by a hunter. CWD has also been diagnosed in farmed elk and deer herds in a number of states and in two Canadian provinces. The first positive farmed-elk herd in the United States was detected in 1997 in South Dakota. Since then, additional positive elk herds and farmed white-tailed deer herds have been found in South Dakota (7), Nebraska (4), Colorado (10),
Oklahoma Oklahoma (; Choctaw: ; chr, ᎣᎧᎳᎰᎹ, ''Okalahoma'' ) is a state in the South Central region of the United States, bordered by Texas on the south and west, Kansas on the north, Missouri on the northeast, Arkansas on the east, New ...
(1), Kansas (1),
Minnesota Minnesota () is a state in the upper midwestern region of the United States. It is the 12th largest U.S. state in area and the 22nd most populous, with over 5.75 million residents. Minnesota is home to western prairies, now given over t ...
(3),
Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columb ...
(1), Wisconsin (6), and New York (2). As of fall of 2006, four positive elk herds in Colorado and a positive white-tailed deer herd in Wisconsin remain under state
quarantine A quarantine is a restriction on the movement of people, animals and goods which is intended to prevent the spread of disease or pests. It is often used in connection to disease and illness, preventing the movement of those who may have been ...
. All of the other herds have been depopulated or have been slaughtered and tested, and the quarantine has been lifted from one herd that underwent rigorous surveillance with no further evidence of disease. CWD also has been found in farmed elk in the Canadian provinces of
Saskatchewan Saskatchewan ( ; ) is a Provinces and territories of Canada, province in Western Canada, western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on t ...
and
Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest T ...
. A retrospective study also showed mule deer exported from
Denver Denver () is a consolidated city and county, the capital, and most populous city of the U.S. state of Colorado. Its population was 715,522 at the 2020 census, a 19.22% increase since 2010. It is the 19th-most populous city in the Unit ...
to the
Toronto Zoo The Toronto Zoo is a zoo located in Toronto, Ontario, Canada. Encompassing , the Toronto Zoo is the largest zoo in Canada. It is divided into seven zoogeographic regions: Indo-Malaya, Africa, Americas, Tundra Trek, Australasia, Eurasia, and the ...
in the 1980s were affected. In June 2015, the disease was detected in a male white-tailed deer on a breeding ranch in
Medina County, Texas Medina County is a county located in the U.S. state of Texas. As of the 2020 census, its population was 50,748. Its county seat is Hondo. The county is named for the Medina River. The extreme northern part of the county lies within the Edw ...
. State officials euthanized 34 deer in an effort to contain a possible outbreak. In February 2018, the Mississippi Department of Wildlife, Fisheries, and Parks announced that a
Mississippi Mississippi () is a state in the Southeastern region of the United States, bordered to the north by Tennessee; to the east by Alabama; to the south by the Gulf of Mexico; to the southwest by Louisiana; and to the northwest by Arkansas. Miss ...
deer tested positive for chronic wasting disease. Another Mississippi whitetail euthanized in Pontotoc County on 8 October 2018 tested positive for CWD. The disease was confirmed by the National Veterinary Services Laboratory in
Ames, Iowa Ames () is a city in Story County, Iowa, United States, located approximately north of Des Moines in central Iowa. It is best known as the home of Iowa State University (ISU), with leading agriculture, design, engineering, and veterinary me ...
on 30 October 2018. Species that have been affected with CWD include elk, mule deer, white-tailed deer,
black-tailed deer Two forms of black-tailed deer or blacktail deer that occupy coastal woodlands in the Pacific Northwest of North America are subspecies of the mule deer (''Odocoileus hemionus''). They have sometimes been treated as a species, but virtually all r ...
, and moose. Other
ruminant Ruminants (suborder Ruminantia) are hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The ...
species, including wild ruminants and domestic
cattle Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus '' Bos''. Adult females are referred to as cows and adult ...
,
sheep Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus '' Ovis'', in everyday usage it almost always refers to domesticate ...
, and
goat The goat or domestic goat (''Capra hircus'') is a domesticated species of goat-antelope typically kept as livestock. It was domesticated from the wild goat (''C. aegagrus'') of Southwest Asia and Eastern Europe. The goat is a member of the a ...
s, have been housed in wildlife facilities in direct or indirect contact with CWD-affected deer and elk, with no evidence of disease transmission. However, experimental transmission of CWD into other ruminants by intracranial inoculation does result in disease, suggesting only a weak molecular species barrier exists. Research is ongoing to further explore the possibility of transmission of CWD to other species. By April 2016, CWD had been found in captive animals in South Korea; the disease arrived there with live elk that were imported from Canada for farming in the late 1990s.Rachel Becker for Nature News. April 18, 201
Deadly animal prion disease appears in Europe
/ref> In the summer of 2018, cases were discovered in the Harpur Farm herd in Grenville-sur-la-Rouge,
Quebec Quebec ( ; )According to the Canadian government, ''Québec'' (with the acute accent) is the official name in Canadian French and ''Quebec'' (without the accent) is the province's official name in Canadian English is one of the thirte ...
. Over the course of 2018, 12% of the
mule deer The mule deer (''Odocoileus hemionus'') is a deer indigenous to western North America; it is named for its ears, which are large like those of the mule. Two subspecies of mule deer are grouped into the black-tailed deer. Unlike the related whi ...
that were tested in
Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest T ...
, had a positive result. More than 8% of Alberta deer were deemed seropositive. In 2022, it had been recorded that outbreaks of CWD had shown themselves in both the United States and Canada. CWD was present in 29 states, infecting herds of moose, deer and elk in 391 different counties. Alabama (1), Arkansas (19), Colorado (27), Idaho (1), Illinois (19), Iowa (12), Kansas (49), Louisiana (1), Maryland (1), Michigan (9), Minnesota (7), Mississippi (9), Missouri (21), Montana (23), Nebraska (43), New Mexico (3), New York (1), North Carolina (1), North Dakota (7), Ohio (2), Pennsylvania (14), South Dakota (19), Tennessee (14), Texas (7), Utah (7), Virginia (10), West Virginia (5), Wisconsin (37) and Wyoming (22).


Europe

In 2016, the first case of CWD in Europe was from the Nordfjella wild reindeer herd in southern
Norway Norway, officially the Kingdom of Norway, is a Nordic countries, Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of ...
. Scientists found the diseased female reindeer as it was dying, and routine CWD screening at necropsy was unexpectedly positive. The origin of CWD in Norway is unknown, whereas import of infected deer from Canada was the source of CWD cases in
South Korea South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korea, Korean Peninsula and sharing a Korean Demilitarized Zone, land border with North Korea. Its western border is formed ...
. Norway has strict legislation and rules not allowing importation of live animals and deer into the country. Norway has a
scrapie Scrapie () is a fatal, degenerative disease affecting the nervous systems of sheep and goats. It is one of several transmissible spongiform encephalopathies (TSEs), and as such it is thought to be caused by a prion. Scrapie has been known since ...
surveillance program since 1997; while no reports of scrapie within the range of Nordfjella reindeer population have been identified, sheep are herded through that region and are a potential source of infection. In May and June 2016, two infected wild moose (''Alces alces'') were found around 300 km north from the first case, in
Selbu Selbu is a municipality in Trøndelag county, Norway. The administrative centre of the municipality is the village of Mebonden. Other villages in Selbu include Flora, Fossan, Hyttbakken, Innbygda, Selbustrand, Trøa, Tømra, and Vikvarvet. T ...
. By the end of August, a fourth case had been confirmed in a wild reindeer shot in the same area as the first case in March. In 2017, the Environment Agency of the Norwegian government released guidelines for hunters hunting reindeer in the Nordfjella areas. The guidelines contain information on identifying animals with CWD symptoms and instructions for minimizing the risk of contamination, as well as a list of supplies given to hunters to be used for taking and submitting samples from shot reindeer. In March 2018, Finnish Food Safety Authority EVIRA stated that the first case of CWD in Finland had been diagnosed in a 15-year-old moose (''Alces alces'') that had died naturally in the municipality of
Kuhmo Kuhmo (known as ''Kuhmoniemi'' until 1937) is a town and a municipality in Finland and is located at the south-eastern corner of the Kainuu region. The municipality has a population of () and covers an area of of which is water. The population ...
in the
Kainuu Kainuu ( sv, Kajanaland) is one of the 19 regions of Finland (''maakunta'' / ''landskap''). Kainuu borders the regions of North Ostrobothnia, North Savo and North Karelia. In the east, it also borders Russia (Republic of Karelia). Culturally ...
region. Before this case in Kuhmo,
Norway Norway, officially the Kingdom of Norway, is a Nordic countries, Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of ...
was the only country in the
European Economic Area The European Economic Area (EEA) was established via the ''Agreement on the European Economic Area'', an international agreement which enables the extension of the European Union's single market to member states of the European Free Trade As ...
where CWD has been diagnosed. The moose did not have the transmissible North American form of the disease, but similar to the Norwegian variant of CWD, an atypical or sporadic form which occurs incidentally in individual animals of the deer family. In Finland, CWD screening of fallen wild deer has been done since 2003. None of the roughly 2,500 samples analyzed so far have tested positive for the disease. The export of live animals of the deer family to other countries has been temporarily banned as a precautionary measure to stop the spread of the CWD, and moose hunters are going to be provided with more instructions before the start of the next hunting season, if appropriate. The export and sales of meat from deer will not be restricted and moose meat is considered safe to eat as only the brain and nervous tissue of infected moose contains prions. In March 2019, the Swedish National Veterinary Institute (SVA) diagnosed the first case of CWD in Sweden. A 16-year old emaciated female moose was found in the municipality of
Arjeplog Arjeplog (; Pite Sami: ) is a locality and the seat of Arjeplog Municipality in Norrbotten County, province of Lapland, Sweden with 1,977 inhabitants in 2010. It is a popular winter test site for the Asian and European car industries and featur ...
in the county of
Norrbotten Norrbotten (), known in English as North Bothnia, is a Swedish province (''landskap'') in northernmost Sweden. It borders south to Västerbotten, west to Swedish Lapland, and east to Finland. Administration The traditional provinces of ...
, circling and with loss of shyness towards humans, possibly blind. The moose was euthanized and the head was sent for CWD screening in the national CWD surveillance program. The brainstem tissue, but not lymph nodes, was positive for CWD (confirmed with Western Blot). A second case of CWD was diagnosed in May 2019, with very similar case history, about 70 km east of the first case. This second case, in the municipality of
Arvidsjaur Arvidsjaur (; sju, Árviesjávrrie; ) is a locality and the seat of Arvidsjaur Municipality in Norrbotten County, province of Lapland, Sweden with 4,635 inhabitants in 2010. Arvidsjaur is a center for the European car industry. During the winte ...
, was also an emaciated and apathic 16-year-old female moose that was euthanized. The circumstances of these Swedish cases are similar to the CWD cases in moose in both Norway and Finland. The EU regulated CWD surveillance runs between 2018 - 2020. A minimum of 6 000 deer are to be tested, both free-ranging animals in the deer family, farmed red deer, and semi-domesticated reindeer. The finding of CWD-positive moose initiated an intensified surveillance in the affected municipalities. Adult hunter-harvested moose and slaughtered semi-domesticated reindeer from the area are tested for CWD. In September 2019, a third moose was found positive for CWD, a hunter-harvested 10-year-old apparently healthy female moose from Arjeplog. A fourth case of CWD in moose was verified in September 2020, in a euthanized 14-year-old lame and unshy female moose in the municipality of Robertsfors, in the county of Västerbotten, approximately 200 km from the previous moose cases in the neighboring county of Norrbotten.


Research

Research is focused on better ways to monitor disease in the wild, live animal diagnostic tests, developing vaccines, better ways to dispose of animals that died from the disease and to decontaminate the environment, where prions can persist in soils, and better ways to monitor the food supply. Deer harvesting and management issues are intertwined.


References


External links

* This entry incorporates public domain text originally a
What is chronic wasting disease?
Animal and Plant Health Inspection Service The Animal and Plant Health Inspection Service (APHIS) is an agency of the United States Department of Agriculture (USDA) based in Riverdale, Maryland responsible for protecting animal health, animal welfare, and plant health. APHIS is the lead ...

Chronic Wasting Disease Alliance


Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georg ...

Chronic wasting disease (CWD) of deer and elk
Canadian Food Inspection Agency The Canadian Food Inspection Agency (CFIA; french: Agence canadienne d'inspection des aliments) is a regulatory agency that is dedicated to the safeguarding of food, plants, and animals (FPA) in Canada, thus enhancing the health and well-being of ...

Chronic wasting disease (CWD)
USGS The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...
National Wildlife Health Center
CWD information & testing
Colorado Parks and Wildlife Colorado Parks and Wildlife manages the state parks system and the wildlife of the U.S. state of Colorado. , the division managed the 42 state parks and 307 wildlife areas of Colorado. , the Colorado Natural Areas Program had 93 designated s ...

Chronic wasting disease Illinois Department of Natural Resources


Minnesota Department of Natural Resources
Chronic wasting disease (CWD)
Nebraska Game and Parks Commission
Chronic wasting disease
New York State Department of Environmental Conservation The New York State Department of Environmental Conservation (informally referred to as NYSDEC, DEC, EnCon or NYSENCON) is a department of New York state government. The department guides and regulates the conservation, improvement, and protection ...

Chronic wasting disease Program
Pennsylvania Department of Agriculture The Pennsylvania Department of Agriculture (PDA) is a cabinet-level agency in Pennsylvania. The department's purpose is to support a sustainable and safe supply of food and agricultural products; be good stewards of the land and natural resources; ...

Chronic wasting disease
Pennsylvania Game Commission The Pennsylvania Game Commission (PGC) is the state agency responsible for wildlife conservation and management in Pennsylvania in the United States. It was originally founded years ago and currently utilizes more than 700 full-time employees and ...

Chronic wasting disease
Wisconsin Department of Natural Resources The Wisconsin Department of Natural Resources (WDNR) is a government agency of the U.S. state of Wisconsin charged with conserving and managing Wisconsin's natural resources. The Wisconsin Natural Resources Board has the authority to set policy ...

Chronic wasting disease (CWD)
Wyoming Wildlife, Wyoming Game and Fish
Chronic wasting disease in Mule Deer


{{DEFAULTSORT:Chronic Wasting Disease Transmissible spongiform encephalopathies Ruminant diseases Animal diseases