Understanding Epizootic Hemorrhagic Disease (EHD): A Threat to Deer Populations

By Derrick R. Stallings – HuntingOfficer.com

Epizootic Hemorrhagic Disease (EHD) is a significant and often devastating viral disease primarily affecting white-tailed deer. While not a direct threat to humans, its impact on deer populations can be severe, leading to widespread mortality events that concern wildlife managers and hunters alike. Let’s delve into what EHD is, its history, its differences from other wildlife diseases like Chronic Wasting Disease (CWD), and what steps can be taken to mitigate its effects.

What is Epizootic Hemorrhagic Disease?

EHD is caused by a virus belonging to the genus Orbivirus, within the family Reoviridae. This same family includes the Bluetongue virus, which causes a similar disease in livestock. In white-tailed deer, EHD manifests as an acute, infectious disease. The virus is transmitted through the bites of tiny insects called midges (genus Culicoides), often referred to as “no-see-ums.” These midges breed in muddy areas around water sources, and their populations tend to boom in late summer and early fall, coinciding with EHD outbreaks.

Once infected, deer typically develop a high fever, lethargy, and a loss of appetite. The virus damages blood vessels, leading to hemorrhages in various tissues, particularly in the mouth, tongue, and gastrointestinal tract. This can cause ulcers, swelling of the head and neck, and a blueish discoloration of the tongue (hence the similarity to Bluetongue). Infected deer often seek water to cool down, and many are found dead near ponds, streams, or lakes. The disease can be rapidly fatal, with deer often succumbing within 8-36 hours of symptom onset. While some deer may recover and develop immunity, severe outbreaks can wipe out a significant portion of a local deer population.

A History of EHD

EHD is not a new phenomenon. The disease was first recognized in North America in 1955, following large-scale deer die-offs in New Jersey and Michigan. However, evidence suggests the virus has likely circulated among deer populations for much longer, possibly going undetected or misdiagnosed in earlier periods.

Since its initial identification, EHD has become an endemic disease in many parts of North America, with outbreaks occurring regularly, especially in the eastern and southeastern United States. The frequency and severity of these outbreaks can vary significantly year to year, largely dependent on environmental factors that influence midge populations, such as rainfall and temperature. Warmer temperatures and drought conditions can lead to concentrated deer populations around dwindling water sources, increasing the likelihood of midge bites and disease transmission. Over time, different strains of the EHD virus have been identified, and deer populations in areas with long-standing EHD exposure may exhibit some level of acquired immunity, leading to less severe outbreaks compared to newly affected regions.

Can Humans Get EHD from Eating Infected Meat?

This is a critical question for hunters and consumers, and the answer is a resounding no.

EHD is not known to be transmissible to humans, even through the consumption of infected deer meat. The EHD virus is highly species-specific, primarily affecting ruminants like deer. While it shares similarities with Bluetongue virus, which can affect livestock like cattle and sheep, neither EHD nor Bluetongue poses a direct threat to human health.

However, while the virus itself isn’t a human health concern, it’s always advisable to exercise caution when handling any wild game. If you encounter a deer that appears sick or is found dead, it’s best not to consume the meat. Animals suffering from EHD are often emaciated and may have secondary bacterial infections, which could affect meat quality and taste, even if the EHD virus itself isn’t harmful to humans. Always practice good hygiene when field dressing and preparing wild game.

EHD vs. Chronic Wasting Disease (CWD): A Stark Contrast

While both EHD and CWD are significant diseases affecting deer, they are fundamentally different in their causes, transmission, symptoms, and potential risks.

Feature	Epizootic Hemorrhagic Disease (EHD)	Chronic Wasting Disease (CWD)
Cause	Virus (Orbivirus)	Prion (abnormally folded protein)
Transmission	Insect vectors (midges/no-see-ums)	Direct animal-to-animal contact, environmental contamination (saliva, urine, feces, carcasses)
Symptoms	Acute: high fever, lethargy, hemorrhages, swelling, rapid death.	Chronic: weight loss, drooling, behavioral changes, poor coordination, death over months.
Duration	Rapid (days)	Prolonged (months to years)
Human Risk	None known	Potential concern, but unproven; generally advised against eating CWD-positive meat.
Impact on Herd	Acute die-offs, localized mortality events.	Chronic decline, gradual population reduction over time.
Environmental	Linked to midge populations and weather conditions.	Prions persist in the environment for years, difficult to eradicate.
Control Measures	Limited direct control; focus on monitoring and understanding outbreaks.	Management of deer populations, carcass disposal, testing, restrictions on movement of deer.

Key Differences Summarized:

• Cause: EHD is viral; CWD is caused by a prion, a misfolded protein.
• Transmission: EHD is vector-borne (midges); CWD is spread through direct contact and environmental contamination.
• Progression: EHD is acute and often rapidly fatal; CWD is chronic and slowly progressive over months or years.
• Human Health: EHD poses no known risk to humans. While there’s no conclusive evidence of CWD transmission to humans, public health agencies generally recommend against consuming meat from CWD-positive animals due to the theoretical potential, given its similarity to mad cow disease.
• Environmental Persistence: The EHD virus does not persist in the environment. CWD prions are incredibly resilient and can remain infectious in soil and on surfaces for years, making eradication extremely challenging.

What Can Be Done About EHD and CWD?

The strategies for managing and mitigating EHD and CWD differ significantly due to their distinct biological mechanisms.

For Epizootic Hemorrhagic Disease (EHD):

Direct intervention to stop an EHD outbreak is largely impractical. Since the virus is transmitted by insects, and deer are wild animals, vaccinating entire wild populations or controlling midge populations over vast areas is not feasible. Therefore, management focuses on:

1. Monitoring and Surveillance: Wildlife agencies closely monitor deer populations for signs of EHD outbreaks. Reporting sick or dead deer to local wildlife authorities is crucial for tracking the disease’s spread and impact. This data helps in understanding the disease’s ecology and predicting future outbreaks.
2. Population Management: In areas experiencing severe EHD outbreaks, wildlife managers may adjust hunting quotas in subsequent years to allow deer populations to recover. Overly dense deer populations can exacerbate disease transmission, so maintaining healthy population levels is indirectly beneficial.
3. Research: Ongoing research into EHD strains, midge biology, and deer immunity is vital for better understanding the disease and potentially developing more effective management strategies in the future.
4. Public Education: Informing hunters and landowners about EHD helps them recognize symptoms, understand the risks (or lack thereof to humans), and report cases effectively.

For Chronic Wasting Disease (CWD):

CWD presents a much more complex and persistent challenge due to the nature of prions and their environmental stability. There is currently no vaccine or cure for CWD. Management strategies aim to contain its spread and reduce its prevalence:

1. Surveillance and Testing: Extensive testing of harvested deer is the cornerstone of CWD management. This helps identify affected areas and track the disease’s progression. Mandatory testing in CWD management zones is common.
2. Carcass Disposal Regulations: Since CWD prions can remain infectious in carcasses and bodily fluids, regulations on how and where hunters can dispose of deer carcasses are critical. This often involves specific landfill disposal or leaving high-risk parts (brain, spinal cord) at the harvest site.
3. Population Reduction: In areas with high CWD prevalence, targeted culls or increased hunting quotas may be implemented to reduce deer density, thereby limiting opportunities for direct and indirect transmission.
4. Restrictions on Live Deer Movement: To prevent the introduction of CWD into new areas, many states have strict regulations or bans on the movement of live deer, particularly from captive cervid facilities.
5. Banning Artificial Feeding/Baiting: Concentrating deer at bait piles or feeders increases nose-to-nose contact and contaminates the environment with saliva, urine, and feces, facilitating CWD transmission. Many states ban or restrict these practices in CWD-positive areas.
6. Public Education: Educating hunters and the public about CWD, its risks, and recommended practices is essential for compliance with management strategies.
7. Research: Ongoing research is critical to develop better diagnostic tools, understand prion transmission, and explore potential long-term solutions, including genetic resistance in deer.

Conclusion

EHD and CWD represent two very different, yet equally important, challenges for wildlife management. While EHD causes acute, often dramatic, die-offs, it typically poses no direct threat to human health and its impact is usually temporary as populations rebound. CWD, on the other hand, is a slow-burning, chronic disease with no known cure, persistent environmental contamination, and a theoretical, albeit unproven, risk to humans. Effective management of both diseases relies heavily on robust surveillance, scientific research, and active participation from hunters and the public to ensure the long-term health of our wild deer populations.