Emerging Wildlife Diseases
An emerging disease is a disease that has recently appeared in a population, or one that is present in a population already but is rapidly increasing in the number of individuals affected or in its geographic range.
There are many factors that can play a role in emerging diseases. These include movement of the pathogen (the organism or agent that causes disease) through trade and travel, change in the home range of the vector (the insect or animal that transmits the disease) due to climate change or physical disruption of the environment, and mutations or evolution of the pathogen over time.
The One Health Concept
Emerging diseases may impact more than one species of animal and can include diseases that affect humans. (Diseases that can be transmitted between animals and humans are referred to as zoonotic). The One Health concept recognizes that the health of people, animals (both wild and domestic), plants and our shared environment are interconnected. Even if a disease-causing organism is specific to wildlife, human actions and interactions with the environment can play a role in how the disease spreads in a wildlife population. The One Health Concept recognizes these relationships and incorporates health professionals and scientists from multiple disciplines (human, animal, environmental) working together. This approach of focusing on the connections between people, animals, plants and their shared environment better addresses health and disease concerns than when humans, animals and the environment are studied separately.
- Rabbit Hemorrhagic Disease Virus
Rabbit Hemorrhagic Disease Virus Serotype 2 (RHDV-2) is a highly contagious viral disease of domestic and wild rabbits. It is not a health risk to humans or other non-rabbit animal species. The disease was first reported in several southwestern states in 2020, causing significant mortality in wild rabbits. Since that time, the virus has been detected in both wild and domestic rabbits in additional states. RHDV-2 was confirmed in Wisconsin for the first time in domestic rabbits in La Crosse County in August of 2022. The disease is of great concern to wild rabbits, as it is highly contagious and has shown to have an extremely high mortality rate in affected populations. If the virus spreads to wild rabbits in Wisconsin, both cottontails and snowshoe hares will be at risk.
The virus is easily spread by infected rabbits and contaminated objects. It can be spread through harvested rabbit meat, on the fur or through blood, urine or feces from infected rabbits. It can be spread by any material that contacts the virus, including surfaces, shoes and clothing. It can be spread by insects through the physical transfer of the virus after landing on contaminated surfaces. The virus can also spread through the feces of predators and scavengers of rabbits.
RHDV-2 is highly stable in the environment. It can be found in dry conditions for up to 15 weeks. It survives freezing. It can stay on surfaces, like clothing, for months.
Rabbits typically die in 1-3 days following infection. Dead rabbits will likely appear to have been in good health. Occasionally blood may be seen around the nose or mouth, but not always.
Preventing the spread of RHDV-2 to Wisconsin
Preventing the introduction of RHDV-2 into wild rabbit and hare populations is the best management practice.
Report wild rabbit and hare illnesses and deaths
Report cases of multiple (three or more) wild rabbit and hare deaths to the DNR Wildlife Switchboard by emailing DNRWildlifeSwitchboard@wisconsin.gov or calling 608-267-0866.
When visiting an area where RHDV-2 has been found, take care to prevent the accidental spread of the disease to Wisconsin. Clothing and footwear worn in areas with known RHDV-2 should be washed before coming home to Wisconsin. Wash equipment, including vehicle tires, with soap and water. Then sanitize with a 10% bleach solution.
Dog Trainers and Trailers, Falconers and Other Small Game Hunters
Wisconsin hunters may encounter rabbits or hares while afield or when working with their dogs.
Resource: This flyer provides steps you can take to help prevent RHDV-2 from coming to Wisconsin.
Information for pet rabbit owners
Domestic rabbit owners can learn more about RHDV-2 on the Wisconsin Department of Agriculture, Trade and Consumer Protection's website.
RHDV-2 does not affect people or domestic animals other than rabbits and hares. However, multiple dead rabbits can also be a sign of tularemia, a disease contagious to people. Do not handle or consume sick or dead wildlife and do not allow pets to contact their carcasses.
- SARS-COV-2 in Wildlife
As a state wildlife agency, we are responsible for protecting populations of wildlife species as held in the public trust. When faced with a contagious disease that may pose a risk to wildlife, the priority is on ensuring that wildlife populations survive and thrive.
SARS-CoV-2, the virus that causes the human disease known as COVID-19, is an emerging virus that health experts continue to get a greater understanding of through research. This process includes a scientific evaluation of how this virus affects not only humans but other animals including wildlife. Some of the early data has revealed that specific wildlife groups may be at increased risk of becoming infected with the virus as well as being able to shed the virus. However, the Wisconsin Department of Health Services reports that the risk of animals spreading SARS-CoV-2, the virus that causes COVID-19, to people is low but that people can spread SARS-CoV-2 to animals, especially during close contact.
Currently, there is very little information regarding how the virus interacts in wild animal populations. However, the risks include:
- Spillover of the virus from human populations into wildlife populations: This would occur from individual wild animals becoming sick from being exposed to a human (with or without symptoms) carrying the virus. Reducing the Risk of SARS-CoV-2 Spreading between People and Wildlife
- Establishment in wildlife species populations: This means that the wildlife species that are susceptible to the virus not only develop illness but act as a competent reservoir for the virus and maintain it in the population as a source of infection for others of that species or other susceptible species. This could also allow the virus to mutate within these species and generate a new form of the virus.
- SARS-CoV-2 becomes established in wildlife populations and becomes a reservoir for human infections: There is currently not enough information to know if wild animals that are infected with the virus could become a source of infection for humans.
There is limited availability for testing wildlife. Tests are not validated for wildlife species, meaning that the test has not been proven to give accurate results in non-humans. Before testing sick or dead wildlife for SARS-CoV-2, more common causes of illness and death are ruled out, unless there is cause for suspicion of exposure to SARS-CoV-2.
Wildlife species that appear to be susceptible to SARS-CoV-2
Wild animal species that have been infected include several types of big cats, otters, and non-human primates in zoos, farmed mink and wild white-tailed deer. One wild mink around the infected mink farm in Utah also tested positive.
While the original virus shows similar genetics to a virus carried by bats found in Asia, it is currently unknown 1) if the virus has or will spillover to North American bats, 2) if these bats are susceptible to infection and if they could serve as a new reservoir for the disease, or 3) if the virus will result in morbidity and mortality, particularly in bats weakened by white-nose syndrome or other stressors.
Other wildlife species and SARS-CoV-2
Research suggests that raccoons do not shed the virus at levels that would spread it in the wild, but other species may.
- Experimental susceptibility of North American raccoons (Procyon lotor) and striped skunks (Mephitis mephitis) to SARS-CoV-2
- Survey of peridomestic mammal susceptibility to SARS-CoV-2 infection
Wildlife species in Wisconsin that appear to be susceptible to SARS-CoV-2
Wildlife species in Wisconsin that are potentially susceptible to the virus include bobcat, American mink, North American river otter, fisher, badger, short-tailed weasel, long-tailed weasel, least weasel, American marten and white-tailed deer.
SARS-COV-2 and bats
Evidence suggests that the SARS-CoV-2 virus may have originated in non-North American bat species, and this virus is closely related to other coronaviruses found in bats. Because of this, free-ranging bats are a key group of concern of being susceptible to infection by the virus transmitted to them from humans and possibly becoming a reservoir for the long-term source of the virus. Currently, SARS-CoV-2 has not been detected in North American bat species.
- Possibility for reverse zoonotic transmission of SARS-CoV-2 to free-ranging wildlife: A case study of bats
SARS-COV-2 and white-tailed deer
Studies in laboratory settings by the U.S. Department of Agriculture (USDA) found that white-tailed deer are susceptible to SARS-CoV-2, the virus that causes COVID-19 in people, and that the virus can spread from deer to deer. Deer in the study showed little to no clinical signs of disease.
Additionally, a survey by the USDA found that some free-ranging white-tailed deer have been exposed to SARS-CoV-2. The USDA tested blood from wild deer in Illinois, Michigan, Pennsylvania and New York and detected SARS-CoV-2 antibodies. No deer from Wisconsin were included in the study. The USDA also reported that a wild white-tailed deer in Ohio was positive by a PCR test for SARS-CoV-2 during testing as part of ongoing deer damage management activities in that state. Further testing of wild deer in Ohio conducted in early 2021 found 35% were positive for the virus. Results from a study conducted by the University of Pennsylvania and the Iowa DNR of captive and wild white-tailed deer sampled in Iowa from April 2020 to January 2021 suggest there was a spillover of SARS-CoV-2 from humans to free-ranging and captive deer with deer-to-deer transmission occurring in those same areas. There is no indication that SARS-CoV-2 is currently causing clinical disease in free-ranging white-tailed deer. More research and surveillance will be needed to fully understand the actual amount of exposure in different deer populations and the implications of these findings, if any, for wild white-tailed deer. Wisconsin is participating in a nationwide surveillance project led by USDA studying SARS-CoV-2 in wild white-tailed deer.
Implications for Wildlife Rehabilitation in Wisconsin
There is no evidence that SARS-CoV-2, the virus that causes COVID-19 in people, can be transmitted to people through handling or eating wild game. Person-to-person transmission is still the greatest risk for spreading COVID-19.
There are no documented cases of humans becoming infected with SARS-CoV-2 from white-tailed deer, and the risk is likely low. However, hunters can be exposed to other diseases when processing or eating the game. Hunters should always practice good hygiene when processing animals by following these recommendations from the Department of Health Services and can also choose to further reduce any potential risk by utilizing additional personal protective equipment such as a mask while field dressing deer.