Cause
Hemorrhagic disease (HD) is a viral disease of white-tailed deer. It can be caused by one of two closely related viruses, epizootic hemorrhagic disease virus (EHDV) or bluetongue virus (BTV). Records of deer die-offs consistent with HD date back to as early as 1886.
Species Affected
White-tailed deer appear to be the only wildlife species affected by EHDV and BTV in Alabama. EHDV rarely affects domestic livestock, but impacts from BTV are well-known in cattle, sheep, and goats, with sheep being the most susceptible. The viruses are not known to cause disease in humans.
Distribution of Disease
HD is not distributed uniformly throughout the range of white-tailed deer. States at more northern latitudes do not have outbreaks as often, but when HD does appear, infection and mortality are most often severe. Most states in the Deep South, including Alabama, have outbreaks virtually every year, but the severity is most often minimal, or even unapparent, in most years. This lack of outbreak severity indicates there may be at least some level of natural resistance to HD’s impacts on southern deer populations.
Evidence of HD has been documented in 66 of Alabama’s 67 counties. Reports of HD activity are typically received from 15-25 counties each year. Reports range from evidence of HD exposure in hunter killed deer (e.g., sloughing hooves, etc.) to localized mortality events in late summer/early fall.
Significance
HD is a common disease of white-tailed deer throughout Alabama, with evidence of virus activity showing up annually. Fortunately, the severity of these events is usually minimal, with very few deer mortalities resulting from virus exposure.
Transmission
The BTV and EHDV are transmitted by biting flies or midges in the genus Culicoides. These flies are commonly known as no-see-ums, sand gnats, sand flies, and punkies. Disease transmission does not occur directly through deer-to-deer contact, but rather indirectly when an infected deer is bitten by one of the insect vectors, which in turn bites uninfected deer and transfers the virus. These biting flies are found near mud, so outbreaks typically occur during the driest part of late summer and early fall when deer congregate near water sources and insect populations are at their peak.
HD activity typically ends when the first hard frost occurs, which kills the insects. It is unclear how the viruses persist through the winter when the insect vectors are inactive. It is thought that in years with unusually mild weather, insect populations may remain active through the winter. This may create opportunities for year-round virus transmission.
Clinical Signs
All clinical signs of HD exposure are the result of damage to blood vessel walls caused by the viruses. These signs change as the disease progresses. Deer typically develop clinical signs about seven days after exposure. Initially, sick deer may be depressed and feverish, with a swollen head, neck, tongue and eyelids, and have difficulty breathing. Sick deer are often found near or in water in a response to the fever.
Death may occur with one to three days of onset of these clinical signs. In most instances in Alabama and other portions of the Deep South, deer survive the initial exposure to the virus, but may become lame, lose their appetite, or reduce activity. Even fewer exposed animals may be disabled for weeks or months by lameness and emaciation.
Diagnosis
Confirmation of exposure to BTV or EHDV must be made using laboratory tests of various tissues, most often blood, spleen, or lung. Swollen tongue, extensive hemorrhaging of internal organs (e.g., heart, lungs, intestines, etc.), and increased fluid surrounding the heart can provide a tentative diagnosis of HD during filed necropsies, but final diagnosis should be confirmed in the laboratory.
A commonly observed sign that deer may have been exposed to HD during the previous summer or fall is sloughing hooves on hunter harvested deer. The virus often causes an interruption in hoof growth, which can make all four hooves appear broken or ringed. The tips of one or more of the hooves may slough, or fall, off. This can cause deer to be unable to walk normally or not at all in the worst cases. This condition typically is evident through the end of Alabama’s deer season.
Treatment
There is currently no treatment for hemorrhagic disease in deer populations.
Summary
HD is an endemic disease of white-tailed deer that shows up each year to some degree in Alabama. Fortunately, the state’s native deer populations appear to have at least some level of resistance to the virus, which makes the disease’s impacts on management of white-tailed deer much less severe than what occurs in some more northern states.
Acknowledgements
Much of this text was taken from the Hemorrhagic Disease of White-tailed Deer brochure produced by the Southeastern Cooperative Wildlife Disease Study, College of Veterinary Medicine, The University of Georgia, Athens, GA 30602 and is used with their permission.
View or Download the Brochure
Suggested Reading
Michigan Department of Natural Resources. Wildlife. Wildlife Disease Manual. Epizootic Hemorrhagic Disease in White-tailed Deer.
Mississippi Department of Wildlife, Fisheries, and Parks. Wildlife & Hunting. Deer Program. Disease. Diseases and Abnormalities. Hemorrhagic Disease & the White-tailed Deer.
Pennsylvania Game Commission. Wildlife. Wildlife Related Diseases. Epizootic Hemorrhagic Disease.
Virginia Department of Game and Inland Fisheries. Hunting. White-tailed Deer. Hemorrhagic Disease.
