Epizootic hemorrhagic disease (EHD) is a hemorrhagic disease of

white-tailed deer The white-tailed deer (''Odocoileus virginianus''), also known as the whitetail or Virginia deer, is a medium-sized deer native to North America, Central America, and South America as far south as Peru and Bolivia. It has also been introduced t ...

(''Odocoileus virginianus'') caused by an infection of a

virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsk ...

from the genus ''

Orbivirus ''Orbivirus'' is a genus of double-stranded RNA viruses in the family ''Reoviridae'' and subfamily '' Sedoreovirinae''. Unlike other reoviruses, orbiviruses are arboviruses. They can infect and replicate within a wide range of arthropod and ver ...

'' subsequently called ''

Epizootic hemorrhagic disease virus ''Epizootic hemorrhagic disease virus'', often abbreviated to EHDV, is a species of the genus ''Orbivirus'', a member of the family ''Reoviridae''. It is the causative agent of epizootic hemorrhagic disease, an acute, infectious, and often fatal ...

'' (EHDV). It is an infectious, and sometimes fatal, virus that is characterized by extensive

hemorrhage Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, v ...

s, and is found throughout the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

. Large-scale outbreaks in wild

ruminant Ruminants (suborder Ruminantia) are hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The ...

s affect

livestock Livestock are the domesticated animals raised in an agricultural setting to provide labor and produce diversified products for consumption such as meat, eggs, milk, fur, leather, and wool. The term is sometimes used to refer solely to animal ...

and the production industry. EHD has been found in some domestic ruminants and many species of deer including white-tailed deer,

mule deer The mule deer (''Odocoileus hemionus'') is a deer indigenous to western North America; it is named for its ears, which are large like those of the mule. Two subspecies of mule deer are grouped into the black-tailed deer. Unlike the related whi ...

, elk, and

pronghorn antelope The pronghorn (, ) (''Antilocapra americana'') is a species of artiodactyl (even-toed, hoofed) mammal indigenous to interior western and central North America. Though not an antelope, it is known colloquially in North America as the American ante ...

.Center for Food Security and Public Health. 2006. Diseases Caused by the Epizootic Hemorrhagic Disease Virus Serogroup. Institute for International Cooperation in Animal Biologics. http://www.cfsph.iastate.edu/Factsheets/pdfs/epizootic_hemorrhagic_disease.pdf Seropositive

black-tailed deer Two forms of black-tailed deer or blacktail deer that occupy coastal woodlands in the Pacific Northwest of North America are subspecies of the mule deer (''Odocoileus hemionus''). They have sometimes been treated as a species, but virtually all r ...

fallow deer ''Dama'' is a genus of deer in the subfamily Cervinae, commonly referred to as fallow deer. Name The name fallow is derived from the deer's pale brown colour. The Latin word ''dāma'' or ''damma'', used for roe deer, gazelles, and antelopes ...

red deer The red deer (''Cervus elaphus'') is one of the largest deer species. A male red deer is called a stag or hart, and a female is called a hind. The red deer inhabits most of Europe, the Caucasus Mountains region, Anatolia, Iran, and parts of we ...

wapiti The elk (''Cervus canadensis''), also known as the wapiti, is one of the largest species within the deer family, Cervidae, and one of the largest terrestrial mammals in its native range of North America and Central and East Asia. The comm ...

, and

roe deer The roe deer (''Capreolus capreolus''), also known as the roe, western roe deer, or European roe, is a species of deer. The male of the species is sometimes referred to as a roebuck. The roe is a small deer, reddish and grey-brown, and well-adapt ...

have also been found, which essentially means that they were exposed to the disease at some time in the past but may not be involved in transmission. Outbreaks of EHD have been reported in

cattle Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referred to as cows and adult ma ...

, although they rarely develop

disease A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that a ...

or die.

Sheep Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus '' Ovis'', in everyday usage it almost always refers to domesticated ...

may develop clinical signs, but this is also rare. EHD is often called bluetongue, but this is incorrect. ''

Bluetongue virus Bluetongue disease is a noncontagious, insect-borne, viral disease of ruminants, mainly sheep and less frequently cattle, yaks, goats, buffalo, deer, dromedaries, and antelope. It is caused by ''Bluetongue virus'' (''BTV''). The virus is ...

'' is closely related to EHDV, and has similar clinical signs, but it is a different disease. Bluetongue is a serious disease in cattle, as well as other ruminants, and can have a significant effect on international trade. Testing at animal health laboratories is necessary to distinguish between the viruses that cause bluetongue and EHD.

Geographic distribution

The distribution of EHD depends greatly on the distribution and abundance of the biting midge ('' Culicoides variipennis''), the level of existing immunity in deer, and the genetic variations in susceptibility. EHD is found in North America, Australia, Asia, the Middle East and Africa. Seropositive animals have also been found in South America. It occurs most often in the

Southern United States The Southern United States (sometimes Dixie, also referred to as the Southern States, the American South, the Southland, or simply the South) is a geographic and cultural region of the United States of America. It is between the Atlantic Ocean ...

, although its distribution is not uniform. In the south, the disease is characterized as frequent and mild, whereas in the north, the disease is characterized as infrequent, severe, and capable of high mortality. EHD can occur throughout Indiana, where the disease can be characterized by both significant outbreaks that occur on a 5- to 10-year cycle that affect the entire state and smaller outbreaks that may only involve a few counties.

Transmission

Transmission of EHD occurs by a host being bitten by a virus-carrying fly or midge. Many different species of culicoides can carry this virus, but the most common carrier is thought to be ''Culicoides variipennis''. EHD can only be transmitted by a vector, meaning it cannot be transmitted from animal to animal, but only through the initial bite by a vector. Ordinarily, EHD outbreaks reoccur within an area primarily during seasonal dry spells. Outbreaks typically result in large die-offs, and smaller and more isolated outbreaks can be common. The midge larvae hatch and live near the water's edge in the bank. They grow and typically remain in the submerged mud in water that is less than 2 inches deep. They continue to live in eutrophic areas, as these areas provide the highest likelihood of survival for the larvae and the midge as it matures. The midges do not survive long after the first seasonal frost.

Clinical signs

Deer may become infected with peracute, acute, or chronic EHD infections. They can develop clinical signs in as few as 7 days after exposure, and this is most constantly characterized by sudden onset of the disease. In general, deer infected with EHD lose their appetite, lose their fear of people, grow weak, show excessive salivation, develop a rapid pulse, have a rapid respiration rate, show signs of a fever, which includes lying in bodies of water to reduce their body temperature, become unconscious, and have a blue tongue from the lack of oxygen in the blood. The heads and necks of infected deer may swell. One of the most common characteristics of deer with the chronic form of EHD is the sloughing or breaking of the hooves caused by growth interruptions. Deer with chronic EHD often become lame due to these hoof problems. Although they are ill for several weeks, they can eventually recover. Deer with the peracute form of the disease may go into shock 8–36 hours after the onset of symptoms, and are found lying dead. Death is also common in deer with acute EHD, which is generally comparable to peracute EHD and is characterized by excessive salivation, nasal discharge, and hemorrhaging of the skin. Cattle that develop EHD typically have subclinical signs. These infections are less severe than the infections in deer, but they may still exhibit fever, oral ulcers, excessive salivation, lameness, and coronitis (inflammation of the coronary band in hoofed animal). Sheep rarely develop clinical signs, and experimentally infected goats have never been shown to exhibit any signs of EHD. Typically, EHD does not kill livestock, but it may affect the production industry negatively because of effects from the disease such as cattle weight loss and lameness.

Prevention and control

Protection of livestock stables

Reducing midges around livestock stables is a good way of reducing the likelihood of disease transmission. To “midge-proof” a stable, several precautions must be taken. One way to reduce entry of midges into the stable is to add screens with very fine mesh. Although mesh significantly reduces the entrance of midges, it is not 100% “midge-proof” on its own. In addition to the mesh screen, fans can be placed strategically in the stable. Fans are effective in reducing midges because of their small size and poor flying capabilities. Removing breeding pools around livestock is also essential. Midges can breed in pools as small as a hoofprint. Providing a substrate that is well-drained and resists the formation of pools can prevent midges from breeding.

Consumption of Infected Animals

EHD has been shown to not affect humans, and no evidence has been found that the epizootic hemorrhagic disease can be contracted through midge bites or by consuming venison that has been infected with the virus. EHD is exclusive to ruminants, and no cases have been reported of nonruminants exhibiting signs or symptoms that are linked to EHD. Once EHD is contracted, the likelihood of other diseases being contracted increases. As a result of the additional exposure to other infections, consuming venison from animals that are visibly sick is not recommended. Animals that are sick may show obvious signs of extreme fatigue and illness, such as rapid weight loss or lesions or abscesses across the body. Other signs include foaming or frothing of the nose and mouth (similar to rabies), as well as the decay of walls of their hooves.

Farmed or captive deer

Currently, no vaccines for EHD are available. Spraying land with insecticides or larvicides could also decrease the risk of transmission.

Management of breeding sites

Because midges breed in water, management of breeding sites is the best way to reduce their numbers, though this may not be practical in areas with lakes or ponds. However, preventive actions include stopping troughs from overflowing, making sure pipes are not leaking, and removing any standing pools of water. Reducing standing water greatly reduces midge populations in a given area.

History

Epizootic hemorrhagic disease has been around for many years. EHD is thought to have been first found and tracked back to around 1890, and has been responsible for die-offs of many different species across North America. Diseases such as blackleg, blacktongue, bluetongue, mycotic stomatitis, or hemorrhagic septicemia were thought to have been the cause of many of these die-offs. After further analysis, the true causative agent was never confirmed. After further review of the case history and other telltale signs and lesions, seasonal occurrence, and lack of a bacterial agent suggest that they might have been EHD.“DNR Wildlife & Habitat Wildlife Disease.” DNR - Epizootic Hemorrhagic Disease (EHD) in White-Tailed Deer, Michigan Department of Natural Resources, www.michigan.gov/dnr/0,4570,7-153-10370_12150-26647--,00.html.

References

External links

Disease card
{{Webarchive, url=https://web.archive.org/web/20141010141239/http://www.oie.int/en/animal-health-in-the-world/technical-disease-cards/ , date=2014-10-10 Ruminant diseases