Chronic Wasting Disease (CWD)

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photo of a deer in a field

What is Chronic Wasting Disease?

Chronic wasting disease (CWD) is a fatal nervous system disease that impacts cervid (deer family) mammals. In deer, it has a 100% mortality rate.

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What causes CWD?

The prevailing theory is that an infectious protein called a CWD prion causes other brain proteins to change to a diseased form. CWD prions then accumulate in the brain and other nervous tissues, where they physically damage nerve cells. The disease agent mainly targets nervous tissue, but it has been found in other tissues including muscles.

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Which species can contract CWD?

CWD has been found in wild and captive elk, moose, and caribou as well as white-tailed, mule, red, and sika deer. We don’t know if other cervid species are susceptible, and there is no scientific evidence that CWD can be transmitted to species outside the deer family, such as cattle, horses, sheep, goats, or swine. There is no evidence that CWD can infect humans, but public health officials still recommend avoiding exposure to it.

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What are the signs and symptoms of CWD?

CWD symptoms are slow to develop, usually taking five to 36 months to appear; but after they do, the animal normally dies in one to 12 months. Symptoms include unusual or sluggish behavior, loss of bodily functions, weight loss, excessive drooling, excessive thirst, frequent urination, isolation from herd, teeth grinding, holding the head in a lowered position, and drooping ears.

Some of these symptoms, particularly weight loss and weakness, can also be seen after a very severe Maine winter. Rabies, although rare in cervids, may also produce some symptoms in common with CWD, such as erratic behavior and drooling.

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How is CWD diagnosed?

The gold standard CWD testing method is Immunohistochemistry (IHC). IHC involves using antibody-based staining to color a tissue sample from the animal’s brain stem (obex) or neck lymph nodes, and evaluating it with light microscopy.

Most of the deer sampled for CWD in Maine are tested using a more rapid and cost-effective method called enzyme-linked immunosorbant assay (ELISA), through which a color-changing test solution can indicate the presence of prions. Any samples identified with ELISA as having CWD prions would be verified using IHC.

Most CWD tests are conducted on dead animals. Live animals can be diagnosed for CWD by taking a biopsy sample from the animal's tonsils and analyzing it with IHC; but this is only done in certain cervid-management situations.

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Is CWD present in Maine?

CWD has never been found in Maine. The nearest population with CWD is in Pennsylvania, though it was found in New York in 2005 (but not since). It has also been found in moose in Colorado and Wyoming.

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How does CWD spread?

Infected individuals shed CWD prions in urine, feces, saliva, and eye fluids. CWD is likely transmitted by direct contact with infected individuals, or by contact with contaminated soil, leaves, bedding, feed, or water. In mule deer, scientists have found that CWD is transmitted from does to fawns.

When deer have frequent, close contact with each other, such around feeding stations or in fenced enclosures, their risk of CWD transmission rises. Contact between wild and fenced cervids along fence lines can also spread CWD (in either direction).

Sites where CWD-infected cervids died (or were placed) may also become contaminated as tissues decompose. Predators and scavengers can also transmit and spread CWD prions around the environment after consuming infectious parts of CWD-infected cervids. CWD prions are not easily destroyed by environmental factors, heat, or disinfection solutions and can persist outside of a host for many years; and recent research has shown that plants can uptake the disease agent and become a potential disease vector.

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Why are we concerned about CWD in Maine?

Where it occurs, CWD poses serious wildlife management problems. If it emerges in Maine, CWD could destabilize the state’s deer population by reducing adult survival rates (CWD infections are usually found in deer 18 months or older). Monitoring and control of an active CWD outbreak is extremely costly and would divert already-scarce funds and staff resources away from other much-needed programs.

Public perceptions about associated human health risks may erode hunter willingness to harvest deer, leading to unwanted population growth in areas that remain CWD-free. Major reductions in deer hunting – a $200 million+ industry for Maine – would adversely affect our rural state’s economy. Furthermore, concerns about the safety of farmed venison as human food could cause the collapse of Maine's $1 million deer farming industry. All of this makes CWD prevention an urgent State priority.

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What are State agencies doing to prevent a CWD outbreak?

MDIFW, the Maine Department of Agriculture, Conservation, and Forestry (DACF), Maine Wildlife Services (WS), and other state departments all play a role in testing and monitoring Maine’s cervid populations for CWD.

DACF and MDIFW coordinate efforts to prevent CWD from entering the state, and they also work closely with other states, the federal government, and private organizations on various CWD-related topics. Their activities cover three key areas: prevention, monitoring, and outreach.

Preventing CWD introduction: The Maine Department of Agriculture revised its cervid importation rules in 2010, lifting an embargo that had been in place since 2002. Cervid importations are now permitted in conformance with the Department’s rules, which require that animals come from five-year CWD-certified herds as well as from accredited tuberculosis-free herds.

Monitoring wild and farmed deer: Efforts to monitor wild and captive/farmed deer for CWD are increasing nationwide, and Maine is no exception.

In the Wild, plans include testing a representative, statewide sample of the deer harvest for CWD each year for the foreseeable future.

In 1999, Maine agencies worked together to test 299 harvested white-tailed deer from Western Maine for CWD. All were negative.

In 2002, MDIFW began testing a sub-sample of each year’s deer and moose harvest. From the 6,000-8,000 harvested deer and 2,000-3,000 moose that MDIFW biologists examine each year for management purposes, we send ~500 samples to a lab for CWD testing. Thus far, all have been negative.

We also observe hundreds of live deer each year while conducting other field work and respond to hunters who report killing deer that appear to have been injured or ill. To date, we have not observed CWD symptoms in any of these animals.

On the Farm, captive/farmed deer are monitored for the presence of CWD using on-farm health monitoring practices and by testing certain farmed deer for CWD at slaughter.

The Department of Agriculture, Conservation, and Forestry (DACF) monitors the deer on Maine’s licensed deer farms for CWD. Since Autumn 2001, more than 1,900 farm-raised elk and deer have been tested for CWD and all tests have been negative.

Outreach: Good communication helps prevent disease. To that end, MDIFW has issued advisories to hunters, meat processors, taxidermists, deer farmers, and the public, sharing basic facts about CWD and how to lessen the risks of introducing it to Maine. These advisories cover:

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How can the average person help prevent CWD?

  1. Be careful with commercial feeds. In theory, prions from CWD-infected deer could be present in commercial deer and elk foods if they were formulated with rendering products containing CWD-infected meat and bone meal (MBM). In 1997, the U.S. FDA banned the use of ruminant (deer, cattle, sheep, goat) MBM from commercial feeds for ruminants. Assuming 100% FDA compliance, common commercial feeds used to supplement the diets of captive/farmed or wild cervids would now be CWD-free. However, we don’t know if MBM from CWD-infected deer or elk was ever incorporated into commercial ruminant feeds distributed in Maine prior to 1997, nor do we know if commercial feeds formulated for non-ruminants (horse, swine, poultry, dog, and cat) sometimes contain MBM from CWD-infected deer or elk. To safely feed cervids, use only commercially available products formulated specifically for ruminants, or use supplement-free whole grains like oats.

  2. Know the risks of feeding and follow best practices. While it is legal to feed deer in Maine during the winter (December 16 to May 31), the practice carries some risks. Commercial feed considerations aside, the close contact and crowding often seen at winter feeding sites can greatly accelerate the spread of diseases including CWD. Because of its long incubation period, a CWD outbreak among white-tailed deer at feeding sites could spread to a large area long before clinically ill individuals are observed, greatly hampering efforts to control the disease. Of note, a new 2019 law allows the MDIFW Commissioner to prohibit or limit the feeding of deer if there is evidence of CWD. In the meantime, if you do feed wild deer in Maine, spread your feed out on the landscape to avoid concentrating deer in small areas.

  3. Be careful what you eat. Do not eat the eyes, brain, spinal cord, spleen, tonsils, or lymph nodes of any deer, or any part of a deer that appeared sick. CWD proteins were recently found in the muscle tissue of infected mule deer, so humans should avoid eating any meat from infected animals.

  4. If you see a deer or moose showing signs of CWD, take note. Do not kill or handle them, but take a close look and consider whether you should report the sighting to an MDIFW biologist or game warden at the numbers below.

    Only report the sighting if they show ALL OR MOST of the following CWD symptoms: extreme thinness, unaware or unafraid of people, shaking or unable to walk normally, drooling, can't raise the head, and ears drooping.

    While early detection of diseased individuals would be the best way to control or eradicate an outbreak, reports of all encounters with sick deer would quickly overwhelm state agency personnel. Deer (and moose) are subjected to many illnesses and injuries that may cause unusual behavior or unthrifty appearance: healthy deer at feeding sites are easily approached by people, these same deer may appear thin and unhealthy for weeks following a severe winter, and deer injured by vehicles or predators may limp and appear sick. Moose also may appear unhealthy in late winter due to heavy tick infestations and/or lungworm infections.

    Wildlife Biologists and Game Wardens:
    Ashland – (207) 435-3231
    Bangor – (207) 941-4466
    Enfield – (207) 794-1003
    Gray – (207) 287-2345
    Greenville – (207) 695-3756
    Jonesboro – (207) 255-2080
    Sidney – (207) 547-5318
    Strong – (207) 778-3322

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What Can Hunters Do to Help?

  1. Follow Maine’s import laws. Because too little monitoring has been conducted to realistically evaluate and deem any state or province CWD-free, it is illegal to transport high-risk wild deer, caribou, moose or elk carcass parts into Maine from any state or province except New Hampshire. This also applies to cervids killed in commercial hunting preserves everywhere. Specifically, hunters may return to Maine only with boned-out meat, hardened antlers (with or without skull caps), hides without the head portion, and finished taxidermy mounts. If still attached, skull caps should be cleaned free of brain and other tissues.

  2. When hunting out of state, take extra precautions. When hunting deer, moose, caribou, or elk outside of Maine, take the following steps to avoid handling, transporting, or consuming CWD-infected specimens (adapted from the Wisconsin Department of Natural Resources):

    When field dressing,
    wear rubber or latex gloves, and minimize contact with the brain spinal cord, spleen, and lymph nodes. Remove all internal organs and dispose of them by burial or other means that prevents contact with live deer or scavengers. Always use a hunting knife (not one that will be reused in the kitchen), and clean it (and all equipment) of residue before disinfecting in a 50/50 bleach-water solution for 1 hour.

    When cutting and processing,
    wear rubber or latex gloves and minimize handling of brain or spinal tissues. Only cut through the spinal column to remove the head, using a separate knife or saw. Similarly, if removing antlers, use a separate saw for that purpose only. Bone out the meat and remove all fat and connective tissue (the web-like membranes). This will also remove lymph nodes. Dispose of feet, hide, brain, spinal cord, bones, and head by burial or other means that prevents contact by live deer or scavengers; and thoroughly clean and sanitize your work area with a 50/50 bleach-water solution.

    Before consuming the meat,
    if you have more than one deer, be sure to keep meat and trimmings from each one separate. If your out-of-state deer is sampled for CWD testing, wait for the test results before eating the meat.

  3. Don’t use urine-based lures. Instead, hunters should use synthetic, non-urine-based lures. In most cases, the urine used in commercial "doe-in-heat" or other buck lures is collected from captive deer or elk farms. At this time, we do not know whether any captive/farmed deer or elk used by the lure industry have ever contracted CWD, and there are no standardized or widely accepted protocols in place for testing deer lures for CWD prions.

    If these deer or elk are infected, CWD prions may be present in the lures. Once prions are in the environment, they have can remain in the soils for years, creating multiple opportunities for Maine deer to contact and ingest them. Depending upon how they are handled, CWD-contaminated deer lures could also pose human health risks.

    If a hunter chooses to use urine-based lures, they should use caution and avoid placing them on their clothing or skin, or on the ground or vegetation that deer can reach. We strongly recommend using synthetic, non-urine-based lures until further research can show that deer urine does not contain infectious prions.

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Can I Get My Maine Deer, Caribou, Moose or Elk Tested for CWD?

Not on demand. Although our system can accommodate enough samples (less than 1,000) from farm-raised and wild deer to scientifically monitor for CWD, we are not able to routinely test hunter-killed deer, moose, caribou or elk in Maine at this time. This is largely due to the high demand for CWD testing in states known to harbor CWD. Existing CWD tests are expensive, time-consuming, and can only be performed at a few federally approved labs.

Looking for more information? Here's who to contact:

For info on hunting and monitoring of wild deer:
Information Center, Dept. of Inland Fisheries and Wildlife
353 Water Street, 41 SHS, Augusta, ME 04333-0041
(207) 287-8000

For info on regulation of captive or farmed deer or elk:

Michele Walsh, DVM, State Veterinarian
Maine Department of Agriculture
Conservation & Forestry
Augusta, ME 04333
Office: 207-287-7615
Cel: 207-215-6727

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