Hemorrhagic disease (HD), a vector-borne disease of white-tailed deer (WTD, Odocoileus virginianus), is caused by two related orbiviruses, epizootic hemorrhagic disease virus (EHDV) and bluetongue virus (BTV). The HD viruses are transmitted through the bite of infected midges, also called gnats or no-see-ums and are considered the most important viral agents affecting deer populations in the United States. Although elk have been known to be exposed to these viruses, there is no evidence that elk are ever affected by the disease.
In the United States, clinical HD is generally reported in late summer and early fall and is thought to correlate with vector activity. In southern latitudes, where prevalence of EHD virus antibodies is high because of frequent and diverse serotype exposure, most infections result in mild or unapparent disease. Antibody prevalence is low in northern and western states where outbreaks are infrequent and are characterized by severe clinical disease and mortality, including Kentucky, where periodic outbreaks are reported.
Clinical presentation of EHD viral infection varies considerably and ranges from rapid death to chronic disease. Deer infected with EHD or bluetongue viruses may be depressed, feverish, emaciated (very thin), and remain near water in late summer or early fall.
White-tailed deer affected by Epizootic Hemorrhagic Disease
Photo by Joe Lacefield, KDFWR
Hemorrhagic disease is caused by one of two different viruses: epizootic hemorrhagic disease virus or bluetongue virus. The virus is transmitted from animal to animal through the bite of an infected midge. These insects occur in the late summer and early fall, which explains the prevalence of the disease during that time of year. Once there has been a hard freeze the midges die off for the winter, eliminating new cases of HD.
Symptoms vary depending on virulence of the virus and resistance of the deer. Symptoms of HD can be very similar to those of chronic wasting disease (CWD); however CWD has not been found in KY. HD cases are well documented in KY, mostly in the late summer and fall. There are two forms of the disease; symptoms of each are listed below:
- Animals may appear feverish and depressed
- Pronounced swelling of head, neck, tongue, and eyelids
- Respiratory distress
• Internal hemorrhaging
- Highly virulent strains may cause death in 1-3 days
- Carcasses often recovered near water
- Survivors may exhibit evidence of lesions in mouth and in rumen lining
- Sloughing hooves (often seen in fall harvest)
Lesions vary depending on the virulence of the disease. They include edema (swelling) of the head, neck, tongue, conjunctiva, lungs, heart, rumen, and intestines. There may be ulcers in the dental pad, tongue, palate, rumen, and omasum. More chronically-infected deer may have growth interruptions in the hooves or sloughing of hoof walls.
This disease is diagnosed from a blood sample, or from a refrigerated sample of spleen, lung, or lymph node tissue.
Wildlife Management Significance
Hemorrhagic disease is one of the most important diseases affecting white-tailed deer populations in Kentucky and throughout the Southeast. The disease affects deer throughout the Southeast and much of the rest of the country. It probably occurs at a low rate every year, but some years an outbreak may occur, resulting in a large number of deer deaths that are noticeable to the public. Outbreaks are more likely to occur in the northern and more mountainous areas of the range of HD; however, they are still relatively uncommon.
How Many Deer Will Be Lost?
Hemorrhagic disease occurs frequently, but its severity and distribution are highly variable. Past occurrences have ranged from a few scattered mild cases every other year to dramatic widespread outbreaks every 5 to 7 years as in 1997, 2002 and 2003, 2007, and 2012. Death rates are usually are well below 25% of the population, however, no deer population has ever been wiped out by HD, even back in the 1950’s when it was 1st described and deer numbers were a lot lower!
Treatment and Control
There are no known treatments or control of hemorrhagic disease.
What Can Be Done To Prevent HD?
At present there is little that can be done to prevent or control hemorrhagic disease. As with most diseases and parasites of white-tailed deer, impacts will be minimized in deer herds that are maintained at moderate to low densities. The best and only practical means of regulating deer populations is through recreational deer hunting, including the harvest of antlerless deer. Although die-offs of deer due to hemorrhagic disease often cause alarm, past experiences have shown that mortality will not decimate local deer populations and the outbreak will be curtailed by the onset of cold weather.
Public Health Implications
The viruses that cause hemorrhagic disease do not infect humans, and people will not contract these diseases from eating meat from infected animals. Deer with hemorrhagic disease may be more susceptible to other diseases, however, and consumption of a sick-looking animal is not advised.