The two most prevalent wildlife diseases impacting Illinois deer are chronic wasting disease (CWD) and epizootic hemorrhagic disease (EHD). While EHD outbreaks occur occasionally and are usually minor, CWD is a persistent disease that can have significant negative consequences for the deer population if left unmanaged. EHD is often confused with bluetongue, a disease with similar symptoms that can affect sheep and cattle. EHD and bluetongue are different diseases.
Illinois residents and hunters are encouraged to report dead (other than by obvious injuries) or apparently sick deer to Illinois Department of Natural Resources biologists.
Impacts on People
Lyme disease is caused by infection with the bacterium Borrelia burgdorferi. Deer can be the host for ticks, particularly the deer tick (Ixodes dammini), that carry this bacterium. Deer, and other wild mammals, provide food for adult ticks in the form of blood meals. Due to their mobility, deer can move attached ticks long distances before the ticks drop off to lay their eggs on the ground. The eggs develop into larva which then turn into nymphs (immature ticks). People can become infected through the bite of a nymph. Adult ticks can also transmit the bacteria, but it is less common since they are more easily detected and removed prior to transmission.
Symptoms include fever, headache, fatigue, and a characteristic skin rash called erythema migrans. If left untreated, infection can spread to the joints, heart, and nervous system.
Impacts on Livestock
Anaplasmosis, caused by the rickettsia Anaplasma marginale, is an important disease of cattle in North America. White-tailed deer can be carriers even if they show no signs of being infected. Research conducted at Southern Illinois University in Carbondale determined that the occurrence in deer was 0% at 6 months of age and 14% at 2½ years of age.
Bovine brucellosis—commonly called Bang’s disease—is caused by the bacterium Baucella abortus. The principal reservoirs are cattle, not deer as many people believe. Cattle are the usual victims of infection. Brucellosis causes abortion of fetuses, infertility, and reduced milk production. Repeated studies in many states, including Illinois, have shown that deer are not important in the occurrence of brucellosis.
Bovine tuberculosis is a chronic bacterial disease caused by the microorganism Mycobacterium bovis attacking the respiratory system. Primarily a disease of cattle, it can affect other species, including humans and wildlife. Once relatively common in cattle in the United States, the disease has been reduced in cattle by the APHIS Bovine TB Eradication Program.
Spillover into wildlife may maintain the microorganism in the environment and function as a source of reinfection for livestock. Prior to 1994, the disease had been reported in only eight wild white-tailed and mule deer. Active surveillance for the disease in wildlife is under way in Michigan, Minnesota, and Indiana, where the disease has been documented in white-tailed deer.
Impacts on Deer
One of the first studies looking for evidence of SARS-CoV-2, the virus that causes COVID-19, in deer was conducted by the USDA Animal and Plant Health Inspection Service (APHIS) Wildlife Services program. In the study, conducted between January 2020 and March 2021, researchers analyzed a total of 481 serum samples from wild white-tailed deer in Illinois, Michigan, New York, and Pennsylvania. Results of the Wildlife Services study showed that some of the deer in those four states had been previously exposed to SARS-CoV-2. Illinois deer had the lowest exposure with 7 percent of 101 samples containing antibodies to SARS-CoV-2. In Michigan, 67 percent of 113 samples contained antibodies; in New York 19 percent of 68 samples contained antibodies; and in Pennsylvania 31 percent of 199 samples contained antibodies. APHIS wrote a short Question & Answer guide about the results of this study to highlight what is currently known and not known about transmission of COVID-19 and deer. Since that study, free-ranging white-tailed deer have also tested positive for exposure to SARS-CoV-2 in Iowa, Ohio, Oklahoma, and in Quebec, Canada.
It is not currently known how wild deer were originally exposed to SARS-CoV-2. Tracking the spread of viruses and disease through wild populations is difficult, but researchers think that the infected deer were likely exposed through multiple sources: the environment, by other animal species and by people. Once infected, and given their gregarious nature, deer likely began to spread the virus among other local individual deer.
It was noted that the deer in the Wildlife Services study did not show any clinical signs of illness. The researchers explained that the presence of antibodies was the result of the immune system response of the deer to being previously infected and did not necessarily suggest a current infection. Other research has shown that white-tailed deer are susceptible to SARS-CoV-2 infection, but in studies where captive deer have been exposed to the virus, they either did not show signs or had mild signs of illness, including coughing and raspy breathing.
There is currently no evidence that people can get COVID-19 by preparing or eating meat from a deer that is infected with SARS-CoV-2. Heat kills the virus. However, hunters should always practice good hygiene when processing animals by following these food safety recommendations from USDA Wildlife Services:
• Do not allow contact between wildlife and domestic animals, including pets and hunting dogs.
• Do not harvest animals that appear sick or are found dead.
• Keep game meat clean and cool the meat down as soon as possible after harvesting the animal.
• Avoid cutting through the backbone and spinal tissues and do not eat the brains of wildlife.
• When handling and cleaning game: Wear rubber or disposable gloves and do not eat, drink, or smoke while handling the animal.
• When finished handling and cleaning game: Wash your hands thoroughly with soap and water. Clean knives, equipment, and surfaces that were in contact with game meat with soap and water and then disinfect them.
• Cook all game meat thoroughly (to an internal temperature of 165 °F or higher).
• Check with your state wildlife agency regarding any testing requirements for other diseases and for any specific instructions regarding preparing, transporting, and consuming game meat.
The results of these initial studies indicate that white-tailed deer can serve as potential reservoir hosts for SARS-CoV-2. What that will mean for the long-term persistence of the virus, or its future evolution and variants, is not yet known. Researchers believe that there has been spillover from humans to deer and there is known deer-to-deer transmission. Spillback from deer to humans may be possible but there is not yet definitive evidence. Both observational and experimental studies in free-ranging, captive, domestic, and farmed animals have shown that as of January 2022, SARS-CoV-2 has been shown to infect at least 29 non-human mammalian species.
In Illinois, more research is already under way to better understand how SARS-CoV-2 is impacting deer. Beginning in November 2021, USDA Wildlife Services collected opportunistic samples at Illinois Department of Natural Resources hunter-harvest check stations and from other sites in Illinois. This work is ongoing, and the results of that study will be shared when they become available.
Chronic Wasting Disease (CWD)
Chronic wasting disease (CWD) was first found in Illinois in 2002 in Winnebago County. CWD poses a serious threat to deer populations in areas where it occurs.
CWD attacks the nervous system and is contagious among deer, with infection passed between deer and also from contaminated environments. The disease is fatal — there is no treatment or cure. As the disease progresses, deer display abnormal behavior, lose weight, and lose control of normal bodily functions.
A deer with CWD usually dies within about 18 months. During this time the infected deer typically shows signs of the disease only in the last month of life.
Studies to date have found no evidence that humans can contract CWD from contact with deer or from eating venison (muscle). However, the Centers for Disease Control and Prevention provides specific recommendations for minimizing the potential risk of human exposure to CWD.
Annual CWD Surveillance and Management Reports are available from the Illinois Department of Natural Resources.
Clinical Signs of CWD
- Loss of coordination and inability to stand
- Drooping of head and ears
- Severe emaciation and dehydration
- Excessive salivation and nasal discharge
- Walking in set patterns
- No fear of humans
- Teeth grinding
- Excessive thirst
- Difficulty swallowing
- Diminished tone of facial muscles
- Excessive urination
Can people get CWD?
A World Health Organization panel of experts reviewed all available information on CWD and concluded that there is no scientific evidence that CWD can infect people. There have been no reports of people contracting CWD from butchering or eating meat from CWD infected animals.
However, there is much that scientists still do not know about CWD, and we cannot state that transmission of CWD to humans is absolutely impossible.
Is it safe to eat venison?
There is no scientific evidence that CWD is transmissible through consumption of meat from an infected deer. CWD has not been linked to the human Creutzfeldt-Jakob disease in the way that bovine spongiform encephalopathy has been in Europe.
The prion that causes CWD accumulates in certain parts of infected deer—the brain, eyes, spinal cord, lymph nodes, tonsils, and spleen—so these tissues should not be eaten.
As a precaution, health officials advise that no part of any animal with evidence of CWD should be consumed by people or other animals. There is no test that your meat processor can perform to ensure your animal does not have CWD. Experts suggest that hunters take simple, commonsense precautions when field- dressing deer:
- Wear rubber gloves when field dressing carcasses.
- Bone out the meat from your animal.
- Minimize the handling of brain and spinal tissues.
- Wash hands and instruments thoroughly after field-dressing is completed.
- Avoid consuming brain, spinal cord, eyes, spleen, tonsils, or lymph nodes of harvested animals. (Normal field-dressing coupled with boning out of carcass will remove essentially all of these parts).
For more information see Precautions for Handling and Processing deer from the Illinois Department of Agriculture.
Can livestock get CWD?
There is no evidence that CWD can be transmitted under natural conditions to cattle, sheep, or other conventional livestock.
How is CWD diagnosed?
Brain samples and lymph nodes are collected from dead deer and are examined with a microscope using a special stain to identify the CWD prion. The samples must be from freshly killed deer, which makes timing critical.
Testing for CWD is conducted by federally approved laboratories. There is no quick test that you or your meat processor can perform to ensure that your deer does not have CWD.
How is CWD transmitted?
Research has shown that CWD may be transmitted by these means:
- direct contact among deer in a herd
- contact with, or ingestion of, infected bodily fluids (saliva, blood, or urine) or feces.
- exposure to prions from decomposing infected carcasses and bodily waste that can remain in soil for many years. The prions cannot be eradicated easily by environmental factors, heat, or disinfection, so transmission by environmental contamination also may be possible.
What is being done to stop the spread of CWD?
Since 2002, the Illinois Department of Natural Resources has used hunter harvest, supplemented by trained agency sharpshooters, to reduce deer populations in CWD areas. With a contagious infectious disease, the best management strategy is to work toward eliminating the disease and keeping it from spreading to other parts of the state.
A task force comprised of key staff from the Illinois Departments of Natural Resources and Agriculture has developed and implemented plans regarding surveillance of wild deer and captive herds, import and export of deer and elk, and a response to the discovery of CWD in Illinois.
Hunters are asked to participate in the surveillance effort by providing samples of harvested deer when requested and by alerting authorities when deer suspected to have CWD are found.
Although hunter harvest is an important part of the disease management program, hunters tend to distribute themselves throughout available deer habitat based upon their ability to gain access, with preference for higher quality habitat, higher numbers of deer, and lower competition from other hunters. As a result, hunter harvest data is valuable for providing disease surveillance information throughout counties, and hunter harvest is useful for broad-scale control of county deer populations, but it has not been intensive enough at the local level to effectively combat a disease epidemic.
For these reasons, the hunter harvest is supplemented by localized Illinois Department of Natural Resources sharpshooting to allow a focused removal of deer from areas in which CWD is known to occur. Addressing disease control in this fashion at the local level actually allows the department to more effectively fight CWD without drastically reducing deer populations throughout the entire county, as would be the case if a state were forced to use hunting as the only tool for disease control.
All deer taken by Illinois Department of Natural Resources sharpshooters are removed from the property where they were shot, and transported to one of the Illinois Department of Natural Resource’s CWD Field Laboratories. There they are field dressed, samples of lymph nodes and brain tissue are removed for CWD testing, and additional tissue is collected for various research studies.
Landowners are offered deer killed by sharpshooters; if they do not want them the deer go to the food pantry if tested negative for CWD. All meat from deer that test negative for CWD is given to the Northern Illinois Food Bank, which distributes the venison to local food pantries.
Meat from deer that test positive for CWD is disposed of at a commercial incinerator.
The Illinois Department of Natural Resources has a sharpshooting program to accomplish the following:
- acquire additional samples for surveillance testing
- remove as many sick deer as possible
- reduce the herd within known CWD locations in an effort to prevent further spread of the disease
The prevalence of CWD in Illinois has been maintained at 1 to 2% over the infected area. Biologists are confident that the rate of spread of the disease to new areas has been reduced.
No other state or province has tried a sharpshooting program to control CWD that is as intensive or as sustained over the long term as Illinois’ experimental management program. As a result, Illinois’ program is being closely observed throughout the country to serve as a basis for deciding whether sharpshooting programs work.
Illinois Department of Natural Resources biologists have worked with scientists at the Illinois Natural History Survey and the University of Illinois to evaluate whether the northern Illinois CWD sharpshooting activities were proving beneficial in managing CWD. Researchers found that the sharpshooting activities had desirable effects on both density and disease prevalence but that sustained effort was required. In northern Illinois, a significant reduction in deer density generally required at least three years of sharpshooting activities that removed 25 or more deer per square mile annually. Researchers also found that the risk of disease in young deer (fawns and yearlings) and female deer declined in areas where significant sharpshooting occurred. The Illinois Department of Natural Resources will continue to collect data and monitor results over the long term to continue this evaluation process.
Why aren’t all deer tested in counties where CWD is found?
In counties where CWD is known to occur, check stations are required during the traditional firearm deer season but not during archery, muzzleloader, or CWD/late winter seasons. Check stations are in place during the firearm season because the majority of deer harvested (approximately 53%) are harvested during this seven-day season. This provides an efficient opportunity to obtain samples for CWD testing.
Check stations are not in place for the other seasons as the harvest per day for archery, muzzleloader, or CWD/late winter seasons seasons is much lower, and the Illinois Department of Natural Resources does not have adequate staffing to run each station for the number of days required.
The Illinois Department of Natural Resources is, however, interested in obtaining samples from deer taken in CWD counties during archery, muzzleloader or CWD/late winter seasons season. Deer harvested during these seasons can be sampled at CWD sampling vendors or drop-off stations. For a list a complete list of sampling vendors and drop-off stations click:
Epizootic Hemorrhagic Disease (EHD)
Epizootic hemorrhagic disease (EHD) was first identified in Illinois in the 1970s. EHD is a vector-borne viral disease of deer transmitted by insects of the genus Culicoides (often referred to as midges, gnats or “no-seeums”). EHD virus is not transmissible through direct “animal to animal” or “animal to human” contact.
EHD affects bucks, does, adults, fawns and yearlings. Some deer become infected and die within 48 hours, while others are minimally affected. Survivors of EHD infection develop immunity to the virus.
EHD is often fatal to deer, causing fever and severe internal bleeding. The severity of impact on deer populations is not predictable because outbreaks depend on weather conditions that influence the size of the infected midge population.
Drought conditions tend to exaggerate the impacts of EHD, as deer tend to congregate around the limited water sources. Receding water levels around ponds, lakes, streams and rivers result in exposed muddy areas from which the midges hatch. Disease transmission is more likely where deer are concentrated and midges infected with the EHD virus are abundant.
Deer also are attracted to water to combat fever and dehydration. Dead and sick deer often are found near water sources such as lakes, ponds or streams, although a deer carcass found farther from a water source could have succumbed to EHD.
Flooding makes more water available for midges to breed in. This can result in increased EHD outbreaks.
There is no effective management treatment for this disease for deer. The number of infected deer will decrease after a hard frost or freezing temperatures kills the midges or gnats that transmit the disease between deer.
Detailed information on EHD can be found at Illinois EHD Reports.
Clinical Signs of EHD
- Appetite loss
- Loss of fear of humans
- Excessive salivation
- Respiratory distress
- Appearing feverish and depressed
- Pronounced swelling of head, neck, tongue, and eyelids
- Lack of consciousness
- Blue appearance of tongue and other tissues in the mouth due to hemorrhage and lack of oxygen in the blood
- Shocklike state; becoming prostrate and dying, often near water
- Possible evidence of lesions in mouth and in rumen lining
- Possible sloughing hooves (often seen in fall harvest)
Is it safe to eat venison during an EHD outbreak?
Yes, it is safe to eat venison from animals that may have contracted EHD and survived.
Can livestock or pets get EHD?
While EHD can be fatal to deer, it is not hazardous to humans, livestock, or pets. EHD is often confused with bluetongue, a similar disease that can affect sheep and cattle. EHD and bluetongue are different diseases, but they have similar symptoms. Veterinarians treat livestock with suspected cases of bluetongue with anti-inflammatories and antibiotics to manage existing lesions and prevent secondary infections.
Domestic and wild ruminants, such as sheep, goats, cattle, buffalo, deer, elk, and antelope act as vertebrate hosts for EHD and the closely related, and similarly transmitted, bluetongue disease.
How is EHD diagnosed?
EHD is diagnosed from a blood sample or from a refrigerated sample of spleen, lung, or lymph node tissue. There are three clinical manifestations of the disease: peracute, classical (or acute), and chronic forms.
Deer have a high fever, weakness, anorexia (loss of appetite), respiratory distress, and edema (abnormal accumulation of fluids) in the head, neck, and tongue. There is a tendency for bleeding, hemorrhage resulting in bloody diarrhea and blood in the urine, and dehydration. Some deer with the peracute form die 8 to 36 hours before showing clinical signs.
CLASSICAL (or ACUTE) FORM
Symptoms are similar to the peracute form, but the signs are accompanied by hemorrhages in the skin, heart, or gastrointestinal track; redness in the inside of eyelids and mouth; and salivation and nasal discharge that can be tinted with blood. Deer sometimes have ulcers in the tongue, palate, or rumen.
Deer with the chronic form of EHD develop ulcers and scars, along with hemorrhages on the lining of eyelids, membranes, mouth, and intestinal walls that result in weight loss, even when there is plenty of food available. Deer may have detachment of the wall of the hoof, making it hard for them to walk. In deer that recover, abnormal hoof growth may be noted. Some deer survive the chronic form.
How is EHD transmitted?
EHD is caused by a virus carried by insects known as midges. Deer become infected when they are bitten by the insects. The virus is not transmittable between deer or between deer and other animals.
Will all the deer in my area die if there is an EHD outbreak?
EHD may significantly decrease the deer population in a localized area; however, the population generally recovers within a few years. Normally, impacts to county-wide deer populations are not severe and often are difficult to detect, although in significant outbreak years, such as 2012, the impacts can be more far-reaching.
Do drought or hot summer temperatures cause EDH?
A drought is not required for deer to contract EHD; however, significant outbreaks often are associated with droughts and hot temperatures. Drought conditions result in limited water, which concentrates deer in locations with remaining water. Receding water levels around ponds and lakes and along streams and rivers result in exposed muddy areas from which the midges can hatch. Disease transmission is more likely where deer are concentrated and midges infected with the EHD virus are abundant.
What should I do if I see a deer I think has EHD?
Hunters or landowners who find sick or dead deer that they suspect may have EHD are asked to REPORT sick or diseased deer or contact their nearest IDNR field office to make a report. Include a name and contact phone number as well as the county, number of dead deer, sex (if known), and specific location of the deer (distance/direction from the nearest town or intersection of two roads).
Cutaneous fibromas are caused by a virus that results in hairless tumors on the skin. They are common and usually temporary. Fibromas can be found anywhere on the body and vary in size from about ¼ inch to more than 8 inches in diameter. They often have a warty appearance. Transmission occurs by biting insects and possibly by direct contact with various contaminated materials that might scratch the skin. Although these fibromas are easily noticed by hunters and are considered unsightly, they are merely small blemishes and are not considered a threat to deer populations. Occasionally, massive or numerous tumors interfere with the activities of a deer, affecting its sight, respiration, breathing, or walking ability; which can lead to the death of the deer. There is no danger of deer spreading fibromas to domestic stock or other animals, and human infection has not been reported.
Ticks, louse flies, lice, ear mites, and demodectic mange are all common external pests found on white-tailed deer. However, these have little effect on the general health of the animal.
Deer, like most wild animals, have their share of internal parasites. Deer serve as hosts to trematodes, such as the liver fluke, lungworms, stomach worms, meningeal worms, arterial worms, and abdominal worms. Larval tapeworms can be found in white-tailed deer. These internal parasites are not considered health hazards to people.
Nasal bot flies are a normally occurring parasite of deer. Larvae of the bot fly (genus Cephenemyia) normally live in pouches at the back of a deer’s throat. They are most frequently discovered by hunters after hanging a deer carcass for a period of time, as the larvae leave the passages in the head and can be found in the body cavity or on the ground under the hanging carcass. They pose no threat to human or livestock health and safety.