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Facts about Wildlife Diseases: Hemorrhagic Fever in White-Tailed Deer1

Samantha M. Wisely, Charlotte Dow, Sydney L. Cottingham, Hannah M. Barber, and Juan M. Campos Krauer2

Hemorrhagic Disease (HD): What It Is and How It Is Spread

Hemorrhagic disease (HD) is the most important viral disease of white-tailed deer in the United States. The viruses that cause HD do not cause illness in people.

HD is caused by two different viruses, bluetongue virus (BTV), named after the swollen blue tongue found in some infected animals, and epizootic hemorrhagic disease virus (EHDV). Both of these viruses are in the genus Orbivirus and are closely related. These viruses can affect both wild and domestic ruminants. Both viruses are transmitted between animals by tiny, blood-feeding insects called biting midges (Figure 1). When the female biting midge feeds on the blood of an infected deer, the midge can become infected with the virus and then will spread the virus to a new deer when it takes another blood meal (Figure 2). Because the midge that spreads the virus emerges when the weather is warm, infections and the occurrence of sick deer have a seasonal pattern. In Florida, like much of the United States, most cases of HD occur in the late summer and early fall (August–October); however, because of Florida’s subtropical climate, it is possible to see cases of disease into the winter months, especially in south Florida, where hard freezes are rare. In cooler climates, freezing temperatures typically break the cycle of transmission by killing the adult biting midges, ending HD transmission in that year.

Figure 1. 

Relative sizes of common flying insects in Florida. On the left is a black fly, in the middle is a midge, and on the right is a mosquito. The midge (middle) is much smaller and may be very hard to see when in flight.


Credit:

Katherine Sayler


[Click thumbnail to enlarge.]

Figure 2. 

Transmission cycle of hemorrhagic disease viruses in the wild.


Credit:

Katherine Sayler


[Click thumbnail to enlarge.]

Importance of HD in Florida and Beyond

Globally, HD is a disease of ruminants. BTV is the cause of significant economic loss to ruminant livestock production, especially of sheep (Maclachlan et al. 2019). In the United States, EHDV is a naturally occurring disease of wild ruminants, most significantly affecting white-tailed deer (Odocoileus virgnianus) (McVey and MacLach­lan 2015). Large outbreaks have occurred in the northern Midwest and western United States, yet in Florida outbreaks appear fewer and less severe in wild white-tailed deer. For deer farmers in Florida, however, EHDV can be an enormous source of mortality for farm-raised deer.

BTV and EHDV are genetically diverse with multiple serotypes and genetically distinct strains of each virus (Bonneau and MacLachlan 2004, Firth et al. 2017, Maclachlan et al. 2019, Nomikou et al. 2015, Wilson et al. 2015, Wilson et al. 2016).

There are more than 29 serotypes of BTV and 7 recognized ED­HVs that can be distinguished by serological analysis. The viruses are spreading within the United States and around the world, and new virus serotypes have been discovered every few years (Figure 3). Furthermore, there have been profound recent changes in the global distribution and biological behavior of both BTV and EHDV (Maclachlan et al. 2019, Maclachlan et al. 2015a, Maclachlan et al. 2015b, Savini et al. 2011).

In the United States, BTV serotypes 2, 10, 11, 13, and 17 are the most common bluetongue viruses. In Florida, all five established BTV serotypes have been reported in deer. However, other types of BTV have been found in the state, sometimes causing fatal infections in wild and farmed deer (USDA 2013a). Understanding which virus is circulating is important because the type of virus found during an outbreak may not be controlled by avail­able vaccines (see section below “Management of HD in Farm-Raised Animals”). Identifying the species of Culicoides midge that serve as vectors of these viruses is also extremely important, as the range of each Culicoides species varies by global region, as do the serotypes and strains of BTV and EHDV that occur globally (Maclachlan et al. 2019).

In 2006, EHDV-6 was isolated from deceased white-tailed deer in Indiana and Illinois and has since been isolated in white-tailed deer in 16 additional states, including Florida. Previously, only EHDV-1 and EHDV-2 had been isolated in the United States (Ruder et al. 2012). Additionally, HD case numbers are increasing in the northeastern and southeastern United States, including Florida, but the cause of this trend is still unknown (Stallknecht et al. 2015). The overall increase in HD mortalities could be due to the introduction of new viruses from other parts of the world, climatic condi­tions (including droughts and wind patterns), and changes to biting midge populations (Mullens et al. 2004).

Currently, the Southeastern Wildlife Disease Cooperative Study (SWDCS) in Athens, Georgia, actively monitors for new, invasive types of biting midges that may be introduced into the United States from the Caribbean or Central or South America. SWDCS’s long-standing surveillance project not only looks for introduced, “exotic” biting midges but also describes where native midges that vector BTV and EHDV are currently found in the southeastern United States.

Species Susceptible to BTV and EHDV

Both BTV and EHDV can cause hemorrhagic fevers in many different species. Globally, BT is primarily a disease of domestic livestock (sheep, goats, cattle) and deer. In contrast, EHD is a disease of certain species of wild, hoofed animals, especially white-tailed deer (McVey and MacLach­lan 2015).

What species develop EHD? According to the World Organization for Animal Health (OIE), EHD mostly affects white-tailed deer (Odocoileus virginianus) and cattle (OIE 2014). Mule deer may also get sick (Center for Food Security and Public Health (CFSPH) 2015). Sheep, black-tailed deer, red deer, wapiti, fallow deer, and roe deer might also be susceptible (at risk of infection), but usually do not become sick. Recent outbreaks in elk (Cervus canadensis) have occurred in the United States.

What species develop BT? A large number of animals can be infected with BTV including goats, sheep, cattle, buffalo, white-tailed deer, and mule deer. Globally, most cases of BT occur in domestic sheep, but the disease can also affect goats, pronghorn sheep, and bighorn sheep (CFSPH 2015).

Signs of Infection

Signs of infection can vary widely between herds or among individuals; and disease severity can range from very mild to acutely fatal.

EHD

In the classical presentation of EHD, deer become sick 2–7 days after being bitten by an infected midge. Symptomatic white-tailed deer may exhibit high fever, anorexia or dropping of partially chewed feed, progressive weakness, excessive salivation, rapid pulse, and respiratory distress. Soft tissue swelling is one of the more common signs of HD, and affected deer may display swelling (sometimes severe) of the head, neck, tongue, and around the eyes. Deer may also lose their fear of humans. Sick deer typically remain near a source of water. Florida deer farmers frequently report that infected deer walk with a rounded back and as if either one or all of their feet are sore. In many cases of acute EHD, the deer may not display any outward signs of infection and will appear normal to the farmer but will die suddenly with no observable signs of disease. Typical necropsy findings associated with EHD-related mortalities, nonspecific hemor­rhages in many tissues including skin and heart, and ulcers or erosions of the tongue, dental pad, palate, rumen, and abomasum (Savini et al. 2011). Veterinarians and farmers have often noted that the skin of affected deer appears bruised. The bruising is most easily appreciated on the inner thighs and caudal abdomen where the hair is the thinnest. Deer that survive EHD may develop abnormal hoof growth or slough their hoof walls. This is typical of the “chronic” form of the disease, where animals survive initial EHDV infection but fail to thrive in the years following infection. In animals that survive the disease, long-lasting antibodies (protein components of the immune system that help protect an animal from future illness) may protect the animal from infection with the same type of virus temporarily (either EHDV-1, 2, or 6). However, different strains of the EHD virus may circulate in subsequent years, leaving animals with naïve immune systems susceptible to infection with the new EHDV serotype.

Clinical signs of EHD in cattle are similar to those exhibited by BTV-affected deer. Cattle infected with EHDV will show signs of disease in 1% to 18% of cases, but death is rare. Production losses associated with the disease in cattle may be significant, especially in dairy farms (European Food Safety Authority 2009).

BT

Signs of EHD and BT are very similar in white-tailed deer, and diseases caused by the two viruses can be very dif­ficult to tell apart. In deer, non-specific signs such as fever, severe depression, anorexia, and loss of fear of humans have been reported. The lips and tongue may become very swollen and may hang out of the mouth, often becoming blue or purple in color (Figure 3). The muzzle, mouth and tongue, and coronary band of the hoof (the soft skin that the hoof grows from) may all appear bruised. Lesions and inflammation in the mouth caused by the virus can result in drooling, soreness during feeding, or a complete inability to eat.

Figure 3. 

Map of common bluetongue serotypes identified by National Veterinary Services Laboratories (NVSL).


Credit:

Dr. Eileen Ostlund, Associate Director of the National Veterinary Services Laboratories, USDA, APHIS (Ostlund 2015).


[Click thumbnail to enlarge.]

Management of HD in Farm-Raised Animals

There is no treatment for HD once an animal shows signs; with supportive care can be given reduce secondary bacterial infec­tions. The best way to manage HD is to prevent it.

Supportive Care

There is no “cure” for HD, only supportive care that can help get the animal through the infection. Early treatment is best, and giving treatment at the first sign of illness may improve chances of the animal recovering. It is not recom­mended to “dart down” or anesthetize a sick deer. However, in certain cases this is the only way to administer treatment. If possible, give IV fluids and concentrated dexamethasone along with B-complex vitamins and an A, D, and E vitamin complex. Long-acting antibiotics like Draxxin (tulathromycin) or Excede (cetiofur CFA) may also be given. These antibiotics do not kill the virus. Antibiotics are only given to help control bacterial infections in the lungs that can occur because the virus is replicating in the animal and weakening its immune system. Pneumonia is the most common outcome in deer with an HD viral infection, making antibiotics an imperative part of the treatment plan. If the animal is not dehydrated, administering Baytril (enrofloxacin) and subsequent fluids is another option for reducing secondary bacterial infections. Adding electrolytes to the water trough and moving additional water troughs close to the sick animal is also useful because sick deer will often become isolated from the rest of the herd and may be unable to seek water on their own. A probiotic should be added to the deer’s feed if any of the deer in the pen are acting sick or are being treated with medications.

If darting a deer is the only available method of administer­ing treatment, administering a long-acting antibiotic and a concentrated dexamethasone injection is recommended. Note that currently there are no approved treatment protocols or medications for white-tailed deer. Any uses of the above mentioned medications for deer are considered “off-label” and must be administered under the direct recommendation of a licensed veterinarian with whom you have a valid client-patient relationship.

Vaccination

Vaccination of animals against HD is difficult in the United States. Inactivated (killed) vaccines have controlled outbreaks in Europe (BTV-8), but effective vaccines are not available for most North American BTV and EHDV sero­types (McVey and MacLachlan 2015). This is because there are no USDA-licensed vaccines that will protect against all of the different serotypes of viruses that cause HD. At this time (2019), there is only one USDA-licensed vaccine for HD, and it protects only against BTV-10. No cross-protection exists between EHDV and BTV, so vaccination for one virus will not provide protection against the other. In other words, vaccinating against BTV will not protect against EHDV, or vice versa.

It is also important to know that vaccination with the BTV- 10 vaccine will not protect against the other BTVs. BTV-2, BTV-10, BTV-13, and BTV-17 are common in Florida, but other bluetongue viruses have been found. Autogenous vaccines (viruses grown from the tissues or blood of an infected, sick animal) have been developed for both EHD and BT, but their efficacy is doubtful given testing results (Wisely and Sayler 2016). Florida-specific vaccines are currently being manufactured, and researchers at the University of Florida Cervidae Health Research Initiative (https://wec.ifas.ufl.edu/cheri/) are working to determine how well these vaccines work and how they can best be formulated to protect the largest number of animals in the state. Scheduling and administration of vaccines must be done under the direct recom­mendation of a veterinarian with whom you have a valid client-patient relationship.

Integrated Pest Management

HD is a vector-borne infection that is transmitted by biting midges (Culicoides spp.). There are currently no proven biting midge control options known to effectively reduce virus transmission, although pest management techniques can be used to mitigate against virus transmission in some situations (Carpenter 2008). Insect control methods for the control of biting midges include chemical, biological, or physical land management strategies (Pfannenstiel et al. 2015). Each method has advantages and disadvantages. Due to the huge number of Culicoides spp. that may be present during an outbreak of HD and the cost associated with controlling these insects, some control strategies are more feasible than others.

Chemical control methods involve pesticide application at environmental sites where biting midges develop as larvae, or pesticide application directly onto animals on which adult midges feed, such as deer. Chemical control can be very expensive and time consuming because adult midges can occur in huge numbers and chemical applications have a limited lifespan and may need to be reapplied daily in some cases. Targeted treatment of biting midge breeding sites would lessen the amount of chemical application needed, but this targeted treatment would require a better understanding of the biology of midges than is currently available. It is challenging to treat breeding sites directly because biting midge breeding sites may cover huge areas, such as entire stream margins. Physical means of biting midge control involves physically modifying the environment, including changing the location and depth of watering holes and holding captive deer as far away from midge breeding sites as possible (if the breeding sites are even known). Building waterholes that are steep and have rocky edges (rather than sandy or muddy banks) may decrease breeding sites for midges. In combination with removing sick animals from the herd and keeping penned animals within an insecticide-treated barrier, management of the environment can be a practical approach for controlling Culicoides spp., but integrated pest management strategies must be specific to individual deer farming operations for maximum efficacy. Much more research on Culicoides management and HD control is needed in Florida and beyond. Researchers at the University of Florida Cervidae Research Health Initia­tive (CHeRI) are working on this problem here in Florida to aid in developing best management practices for the captive cervid industry.

Best Management Practices for Farmed Deer in Florida

Diagnostics

Diagnostic tools for HD are currently expensive and may involve a significant lag time between sample submission and results. The lack of a comprehensive, affordable toolkit for determining which virus strain an animal has been exposed to or is infected with prevents the understanding necessary to develop prophylactic tools like vaccines.

To improve sensitivity and turnaround time, UF/IFAS is working to streamline virus identification in infected ani­mals. Using improved techniques, the virus can be detected using real-time polymerase chain reaction (PCR) that can be used to quickly determine (usually in under 2 hours) whether or not an animal is infected. Using a simple follow up test, the type of EHDV or BTV can be determined. It is also possible to isolate the virus using fresh samples. From these samples we can determine the genetic code of the entire virus and tell how different it is from or similar it is to viruses circulated throughout Florida. This can give researchers clues as to when and from where new, “exotic” strains of the viruses have been introduced into the state.

Whole-blood collected in EDTA-coated tubes (available from your veterinarian) or spleen samples from dead deer collected as soon as possible after death are the ideal diagnostic specimens. Samples should be refrigerated but not frozen because the virus degrades on direct contact with ice.

The Work of UF/IFAS CheRi (Cervidae Health Research Initiative)

In response to Florida stakeholders, UF/IFAS Cervidae Health Research Initiative (CHeRI) seeks to promote interdisciplinary science, education, and outreach that increase the health and production of captive cervids in a sustainable manner and promote the health of native wildlife and the ecosystems in which they live. In response to the needs of farmers in Florida for controlling HD, we have developed a multi-pronged approach to reduce mortality and increase production in deer and cattle. We have begun collecting data to support the development of an integrated pest management plan and a best farm management plan; we are increasing diagnostic capabilities for detection and management of disease; and we are developing relationships with captive deer farmers and cattle ranchers throughout Florida.

Glossary

Bluetongue virus (BTV) is a vector-borne viral disease that affects wild and domestic ruminants. Infection with BTV is unapparent in most animals, but can cause fatal disease in some infected sheep, deer and wild ruminants.

Epizootic hemorrhagic disease virus is a vector-borne viral disease that affects wild and domestic ruminants, especially white-tailed deer. The acute form of the disease can result in a very high mortality rate in white-tailed deer.

Biting midges are very small flies that can transmit the epizootic hemorrhagic disease and bluetongue viruses. Officially, these tiny insects are members of the genus Culicoides.

Serological analysis is a laboratory test that uses a sample of blood serum, the clear liquid that separates from the blood when it is allowed to clot. The purpose of such a test is to detect serum antibodies that the body puts out to help fight infections.

Rumen and abomasum are two of the four chambers of the stomach of ruminant animals, such as cattle, goats, sheep, deer, and antelope.

Autogenous vaccines are vaccines made from freshly isolated viruses taken from a deer that has died from EHDV or BTV, which is then cultivated in a laboratory. Typically, these types of vaccines are made for use only within the herd from which the animal that died came.

References

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Center of Food Security and Public Health. Iowa State University. Bluetongue factsheet. http://www.cfsph.iastate.edu/Factsheets/pdfs/bluetongue.pdf. Accessed 20 July 2015.

European Food Safety Authority. 2009. Scientific opinion on epizootic hemorrhagic disease. EFSA Journal 7:1418. http://www.efsa.europa.eu/sites/default/files/scientific_output/files/main_documents/1418.pdf Accessed 5 December 2015.

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Footnotes

1.

This document is WEC366, one of a series of the Department of Wildlife Ecology and Conservation, UF/IFAS Extension. Original publication date February 2016. Revised June 2019. Visit the EDIS website at https://edis.ifas.ufl.edu for the currently supported version of this publication.

2.

Samantha M. Wisely, professor, Department of Wildlife Ecology and Conservation; Charlotte Dow, DVM, Royale Veterinary Services; Sydney L. Cottingham, graduate research assistant, Department of Large Animal Clinical Sciences, UF College of Veterinary Medicine; Hannah M. Barber, graduate research assistant, Department of Large Animal Clinical Sciences, UF College of Veterinary Medicine; and Juan M. Campos Krauer, assistant professor, Department of Large Animal Clinical Sciences, UF College of Veterinary Medicine; UF/IFAS Extension, Gainesville, FL 32611.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.