Epizootic Hemorrhagic Disease

Epizootic hemorrhagic disease (EHD) is a hemorrhagic disease of white-tailed deer (Odocoileus virginianus) caused by an infection of a virus from the genus Orbivirus (Shope et al. 1960, Howarth et al. 2001).^[1][2] It is an infectious, and sometimes fatal, virus that is characterized by extensive hemorrhages, and is found throughout the United States. It is important for deer hunters, farmers, farm property owners, and livestock owners to have knowledge about EHD because of the seriousness of this disease, its ability to cause large scale outbreaks in wild ruminants, and its ability to affect livestock and the production industry (EHD in White-tailed Deer: Michigan Wildlife Disease Manual).^[3] Epizootic hemorrhagic disease has been found in some domestic ruminants and many species of deer including white-tailed deer, mule deer, and pronghorn antelope (CFSPH 2006).^[4] Seropositive black-tailed deer, fallow deer, red deer, wapiti, and roe deer 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 although it is rare for them to develop disease or die. Sheep may develop clinical signs; however, this is also rare (Howarth et al. 2001). Epizootic hemorrhagic disease is often called bluetongue; however, this is incorrect. Bluetongue virus is closely related to EHD, 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.

History

EHD was first reported in 1955 in New Jersey, killing 700 whitetails. In Alberta in 1962, EHD killed 440 whitetails, 18 mule deer, and 13 pronghorn. In a 1976 outbreak, thousands of whitetails died from EHD in Nebraska, Wyoming, Kansas, and the Dakotas, and 4000 antelope died in Wyoming. Another 1000 whitetails died from EHD in New Jersey in 1976.^[5]

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 (Gaydos et al. 2004).^[6] Epizootic hemorrhagic disease is found in North America, Australia, Asia, and Africa. Seropositive animals have also been found in South America. Epizootic hemorrhagic disease is known to occur most often in the southern United States, although its distribution is not uniform (Davidson et al. 2002).^[7] 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 (Gaydos et al. 2004). Epizootic hemorrhagic disease can occur throughout Indiana. Outbreaks in Indiana of the disease can be characterized by both significant outbreaks that occur on a 5-10 year cycle that affect the entire state and smaller outbreaks that may only involve a few counties.

Transmission

Epizootic hemorrhagic disease is not contagious (it is not transmitted from deer to deer). It is transmitted by biological vectors In North America, this is most often the biting midge, Culicoides variipennis(Hill and MacDonald 2010).^[8] Other biting gnats and mosquitos may also transmit EHD (CFSPH 2006). Typically, outbreaks occur in late summer to early fall (August to October) and cease with the onset of frost (MDNR), because of the die-off of the biological vectors.

Clinical signs

Deer may become infected with peracute, acute, or chronic EHD infections. Deer can develop clinical signs in as little 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 include 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 (Howarth et al. 2001). The head and neck 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 (CFSPH 2006). 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 (Howarth et al. 2001). 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(CFSPH 1996). 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(CFSPH 2006). Typically, EHD doesn’t kill livestock, but it may affect the production industry negatively because of effects from the disease such as cattle weight loss and lameness. This is a main reason livestock owners and farm owners need to be aware of EHD.

Prevention and control

Protection of livestock stables

Reducing midges around livestock stables is a good way of reducing the likelihood of disease transmission. In order to “midge-proof” a stable, multiple precautions must be taken. One way to reduce entry of midges into the stable is to add screens with very fine mesh. Although, mesh will significantly reduce the entrance of midges, it is not 100% “midge-proof” on its own(Carpenter et al. 2008).^[9] 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(Merck Veterinary Manual 2011).^[10] 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 resist the formation of pools can not only prevent midges from breeding, but can enhance the health of the animals' hooves.

Farmed or captive deer

Currently there are no vaccinations for EHD and it can be deadly in deer. However, if you are managing deer on a site or managing deer in captivity, management of the breeding sites could help reduce the likelihood of transmission of EHD. Also, spraying land with insecticides or larvacides could also decrease the risk of transmission, because EHD is not contagious between animals, but it is transmitted only through midges and, to a lesser degree, other biting insects(CFSPH 2006).

Management of breeding sites

Because midges breed in water, management of breeding sites is the best way to reduce the amount of midges, though this may not be pragmatic in areas where there is a lake or pond. However, you can prevent troughs from overflowing, make sure pipes are not leaking, and remove any standing pools of water (Carpenter et al. 2008). Reducing standing water will greatly reduce the amount of midges in a given area.

Is my deer safe to eat?

Typically, deer that have or may have been affected by EHD should be safe to eat. None of the viruses in the Epizootic hemorrhagic disease serogroup affect humans (Howarth et al. 2001).

References

External links

• Current status of Epizootic Hemorrhagic Disease worldwide at OIE. WAHID Interface - OIE World Animal Health Information Database
• Disease card
• Michigan Department of Natural Resources