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Blue Tongue and EHD

Introduction of Blue Tongue and EHD

Blue Tongue and EHD is the fact that blue tongue can be a virulent disease that mostly impacts domestic cattle, sheep as well and goats. EHD is a viral illness that mostly affects white-tailed deer.

Insects are among the most important agents for the spread of animal disease. They cause major losses to animals. The Blue Tongue (BT) is one of them. Epizootic Hemorrhagic Disorder (EHD) both are virus-borne vector-borne disease which are caused by closely related orbiviruses from the Reoviridae family.

These are hemorrhagic illnesses. The diseases are common in cattle, sheep goats, and whitetail deer. Transmission of both ailments is caused by gnats biting. They trigger similar symptoms like drooling and fever, nasal congestion, and swelling of muscles. The control of gnats is the best approach to control both of these diseases.

What is Blue Tongue?

The Bluetongue virus is a virus that causes conditions that can affect cattle, sheep goats, deer, and sheep. It’s caused by the Bluetongue virus and is not a contagious illness. This means that it doesn’t cause any harm to animals because of contact. It is also known as blue tongue because of the characteristic dark blue-colored tongue of animals suffering from the disease.

Also, the tongue and lips become extremely enlarged, which causes tongues to pop out in the mouth. This condition is typically found in sheep and can be caused by severe illness as well as death of sheep.

Blue Tongue
Figure 01: Blue Tongue

For cattle, it’s rare and can cause loss of fertility. Infection and erosion of the mouth and muzzle, hyperemia, edema, and arterial congestion bleeding, and tissue infarction are a few indications of this condition.

The most common complications which cause death include ulceration and erosion of the oral and nasal cavities the esophagus and the forestomach as well as inflammation and accumulation in the lungs as well as internal hemorrhages. Humans don’t suffer from the blue tongue condition.

The disease is spread by biting insects. To protect animals from blue tongue disease, precautionary steps like the control of insects through the destruction of insect habitats as well as the use of insecticides need to be considered.

What is EHD?

Epizootic Hemorrhagic Disorder (EHD) is the most common viral illness among white-tailed deer. It’s caused by the EHD virus. EHD virus and is a condition that can be seen in any age of deer. It is extremely contagious and may cause numerous deaths. It is true that EHD can be responsible for greater than 90 % of mortality and morbidity in white-tailed deer.

Figure 02: EHD

The symptoms of EHD for deer are fatigue, fever, weakness, and excessive salivation. Other signs include the appearance of facial swelling, hyperaemia in mucous membranes and conjunctivae of the oral cavity an autoimmune condition, stomatitis, or coronitis. excessive salivation.

In the event that EHD is seen for an extended period, there are complications, such as bloody diarrhea haematuria as well as dehydration and death could occur. EHD transmission is caused by bites of gnats which are tiny, less than mosquitoes. It is possible to determine the presence of EHD through the testing of the virus in tissue as well as blood.

Testing for viral infection typically includes the immunofluorescence test and reverse transcriptase-polymerase chain reaction (RT-PCR) tests. Signs of clinical manifestations can be used to determine the presence of the disease in deer. There is no specific cure for EHD aside from treatment.

History of Blue Tongue and EHD

Blue Tongue: Blue Tongue Disease, caused by the Bluetongue virus (BTV), dates back to early 20th century South Africa where it first surfaced, before spreading across the globe and leading to various serotypes being isolated to eventually create vaccines against it in livestock.

Blue Tongue has had significant economic ramifications and economic loss has resulted from its prevalence across cattle, sheep, goats, and other ruminant populations; therefore its ongoing monitoring and management remains essential to livestock producers worldwide.

Epizootic Hemorrhagic Disease (EHD): Epizootic Hemorrhagic Disease, caused by Epizootic Hemorrhagic Disease Virus (EHDV), has long been prevalent across North America. First identified in 1950 in the US, where it affected white-tailed deer. EHD outbreaks typically take place seasonally during late summer and early fall, coinciding with the activity of Culicoides biting midges primary vectors of EHD.

EHD may be less economically damaging to livestock compared to Blue Tongue; however, its association with significant wildlife mortality events among deer populations has raised alarm among wildlife management authorities. Therefore, efforts to study, monitor, and control EHD outbreaks among deer and other affected species remain integral to wildlife conservation.

Where are Blue Tongue and EHD Found

Blue Tongue Disease (BTV): Blue Tongue is found worldwide. It has been reported in North America, Europe, Asia, Africa and Australia; with variations depending on region. Serotype prevalence can differ depending on Culicoides biting midge activity – acting as vectors to the virus that infected it in its formative stages. Blue Tongue can affect domestic as well as wild ruminants.

Epizootic Hemorrhagic Disease (EHD): EHD can be found across North America. The United States is especially prone, and outbreaks often coincide with Culicoides midges during late summer and early fall White tailed deer are most susceptible in North America but EHD cases have also been seen elsewhere, including Europe and Asia; though most frequently it afflicts North American wildlife species.

Symptoms and Clinical Signs: How to Differentiate Blue Tongue from EHD

Blue Tongue Disease (BTV):

  • Blue Tongue Discoloration: One of the hallmark symptoms of Blue Tongue Disease is cyanosis or discoloration of the tongue, gums, and mucous membranes; this symptom occurs less commonly among EHD sufferers.
  • Fever: Animals infected with certain illnesses may display fever that varies in severity.
  • Lameness: Animals inflicted with chronic diseases may experience lameness that could be misinterpreted as other sources of lameness.
  • Drooling and Salivation: Animals affected with Blue Tongue Disease often exhibit excessive drooling and salivation, making for an uncomfortable living situation.
  • Swelling of the Facial Structure: Swelling is another possible sign of Blue Tongue.

Epizootic Hemorrhagic Disease (EHD):

  • Fever: Like Blue Tongue, EHD can also lead to feverish responses in affected animals.
  • Lethargy: Animals that have been infected may appear lethargic and weak. EHD is often marked by mouth ulcers that lead to increased salivation and difficulty eating, leading to excessive salivation and difficulty with eating.
  • Hemorrhaging: EHD sufferers typically exhibit more noticeable hemorrhaging or bleeding compared to Blue Tongue sufferers, often manifesting itself in bloody discharge from the nose, eyes or rectum.
  • Circulatory Disturbances: EHD can result in circulatory disturbances that result in fluid accumulation within chest and abdominal cavities.
  • Swollen Coronary Bands: Some affected animals may develop swollen coronary bands, leading to lameness.

Transmission and Vectors: How are Blue Tongue and EHD Spread?

Blue Tongue Disease (BTV) and Epizootic Hemorrhagic Disease (EHD) are primarily transmitted via Culicoides biting midges that act as vectors for these diseases, serving as blood-feeding insects that transmit their virus responsibly.

When infected ruminants such as deer or cows are bitten by one of these insects, their virus becomes inhaled by them before later spreading via repeated bites by infected midges; transmission then occurs both among livestock populations as well as wildlife populations that are susceptible.

Environmental factors, including temperature and moisture levels, often play a significant role in the spread of these diseases, particularly among livestock populations. Furthermore, the movement of infected animals such as livestock may further spread their infection across multiple locations.

While both diseases share similar transmission mechanisms, their geographic ranges and specific virus serotypes vary between regions, leading to different patterns of spread over time.

Effective management and prevention strategies like vector control or vaccination are necessary in mitigating their negative impact on both livestock and wildlife populations.”

Difference Between Blue Tongue and EHD

Bluetongue is a virulent condition that mostly affects cattle, sheep, as well as goats. EHD is a virulent disease that is mostly found in white-tailed deer. This is the primary differentiator between blue tongues and EHD. Bluetongue is the result of the Bluetongue virus and EHD is due to the Epizootic hemorrhagic virus.

The blue tongue can cause loss of fertility in cattle, however, EHD for cattle is unusual.  Signs of blue tongue disease include ulceration or erosion of the mouth and muzzle and hyperemia, edema as well as hemorrhage, vascular congestion as well as tissue infarction.

The symptoms of EHD include fever, weakness as well as inappetence and excess salivation as well as facial edema and hyperemia in the conjunctivae as well as mucous membranes that line the mouth with stomatitis as well as excessive salivation.

Here’s a comparison chart highlighting the key differences between Blue Tongue Disease and Epizootic Hemorrhagic Disease (EHD):

Characteristic Blue Tongue Disease Epizootic Hemorrhagic Disease (EHD)
Causative Agent Bluetongue virus (BTV) EHD virus (EHDV)
Geographic Distribution Worldwide Mainly North America
Primary Hosts Ruminants (cattle, sheep, deer) Ruminants, especially white-tailed deer
Clinical Signs Blue tongue discoloration, fever, lameness Fever, lethargy, mouth ulcers, hemorrhaging
Transmission Vector Culicoides biting midges Culicoides biting midges
Impact on Livestock Significant economic impact Less significant impact
Wildlife Impact Affects wildlife, including deer Significant wildlife mortality events
Global Prevalence Worldwide presence Mainly limited to North America
Seasonal Occurrence Seasonal patterns Seasonal outbreaks
Vaccination Available Vaccines available Limited vaccines
Zoonotic Potential Not known to affect humans No zoonotic potential
Vector Control Important for prevention Important for prevention

Diagnosis and Testing: Methods for Identifying Blue Tongue and EHD

Clinical Evaluation:

  • Climatic Signs: Veterinarians assess the clinical signs and symptoms exhibited by affected animals, such as fever, lameness, blue tongue discoloration (in BTV cases) or mouth ulcers (EHD cases) among others as indicators for diagnosis.

Laboratory Tests:

  • Serological Tests: Blood samples taken from suspected cases can be tested for specific antibodies directed against BTV or EHDV as causative viruses. Enzyme-linked immunosorbent assay (ELISA) or virus neutralization tests are two commonly employed serological methods.
  • Isolation of the Virus: Animal-derived blood and tissue samples may be used to isolate BTV or EHDV and help determine their presence. Once isolated, further characterization and confirmation may take place to further understand their nature and identity.
  • Polymerase Chain Reaction (PCR): PCR tests can detect viral genetic material (RNA). Specific primers are used to amplify this RNA and enable identification and differentiation between virus serotypes.
  • Pathological Exam: Postmortem exams of deceased animals may reveal characteristic lesions and tissue changes associated with Blue Tongue or EHD, providing additional support for diagnosis. Histopathological analysis can also assist in supporting this diagnosis.

Epidemiological Investigation:

  • Geographic and Temporal Patterns: Examining disease outbreaks based on their geographic and temporal patterns is another powerful indicator. EHD outbreaks tend to cluster mainly in North America while Blue Tongue spreads globally.
  • Understanding Affected Species: As with EHD, understanding which species are predominantly affected – in this instance deer can aid with diagnosis.
  • Vector Activity: Monitoring Culicoides biting midges – vectors responsible for transmitting both diseases is informative.
  • Information About the Past History and Management Practices for Affected Livestock: Information regarding past vaccination history and management practices of affected livestock can help in diagnosing and controlling diseases effectively.
  • Laboratory Confirmation: Confirming specific BTV or EHDV serotypes through laboratory testing can often help confirm definitive diagnoses.

How does Blue Tongue and EHD affect animals?

Blue Tongue Disease (BTV):

  • Clinical Signs: Animals infected with Blue Tongue may display clinical symptoms including fever, lameness and drooling. One characteristic feature of Blue Tongue is blue discoloration of their tongue or other mucous membranes.
  • Swelling: Some animals may experience swelling around their head and face.
  • Reduced Productivity: Blue Tongue disease in livestock such as cattle and sheep may result in decreased feed intake, weight loss, reproductive issues, as well as economic losses for producers.
  • Mortality: Although Blue Tongue tends to be less fatal in livestock settings, it has caused significant mortality among wild ruminant populations, including deer.

Epizootic Hemorrhagic Disease (EHD):

  • Clinical Signs: EHD can cause fever, lethargy, and mouth ulcers in infected animals. Furthermore, hemorrhaging from various body parts is more pronounced with EHD than Blue Tongue.
  • Severe Illness: Erichson-Herrick Disease can lead to severe illness in white-tailed deer herds, often leading to high mortality rates during outbreaks. Animals that become infected may appear weak and starved.
  • Wildlife Impact: EHD poses a grave threat to wildlife populations, particularly deer herds, as it can lead to localized die-offs that threaten both deer populations and hunting activities.
  • Reduced Livestock Performance: Although EHD may not be as economically damaging to livestock as Blue Tongue, it still can result in reduced performance and production losses for affected cattle.

Seasonal patterns of outbreaks Blue Tongue and EHD

Blue Tongue Disease (BTV) and Epizootic Hemorrhagic Disease (EHD) each exhibit distinct seasonal outbreak patterns that are heavily impacted by environmental conditions and the activity of their common vector, Culicoides biting midges.

Blue Tongue Disease (BTV): Outbreaks of Blue Tongue usually follow a seasonal cycle where it is prevalent, often coinciding with Culicoides midges being more active during hot and humid conditions.

Cases often peak between late summer and early autumn when Culicoides midge populations reach their highest point due to factors like temperature and rainfall which influence breeding behaviors of Culicoides midges increasing livestock and wildlife risk of contracting the virus from midge bites during this period.

Epizootic Hemorrhagic Disease (EHD): outbreaks also follow a seasonal pattern, similar to Blue Tongue outbreaks. EHD virus is transmitted primarily by Culicoides midges and its prevalence can vary with temperature and vector activity.

Outbreaks tend to peak between late summer and early fall when midge populations reach their highest point, favoring transmission to susceptible ruminants; this seasonality often leads to localized outbreaks with significant mortality events occurring among white-tailed deer populations.

Prevention and Control Measures

Prevention and control measures for Blue Tongue Disease (BTV) and Epizootic Hemorrhagic Disease (EHD) involve employing several strategies with the aim of mitigating their impact on livestock as well as wildlife populations.

Below are a few key approaches:


  • One of the most effective strategies to combat Blue Tongue and EHD in livestock, vaccines are available against various serotypes to provide immunity and decrease outbreak risk.
  • Routine vaccination in areas where outbreaks may be likely can provide immunity and decrease outbreak risks.

Vector Control:

  • Controlling Culicoides biting midges, the main vectors for BTV and EHDV infections, is essential.
  • Strategies may include insecticide use, traps, and modifications of environmental settings to limit breeding sites for vectors.

 Biosecurity Measures:

  • Biosecurity practices on farms and ranches can help protect against the introduction and spread of viruses, such as quarantining new animals, restricting livestock movement, and minimizing contact between wildlife and affected areas.

 Monitoring and Surveillance:

  • Monitoring for disease presence and activity vectors can help detect outbreaks early and report suspected cases to veterinary authorities in order to ensure rapid response times.

 Wildlife Management:

  • EHD management efforts typically include efforts to decrease deer populations within affected areas in order to limit its spread, while wildlife agencies may implement hunting regulations or population control measures.

 Environmental Management:

  • Altering land use practices to limit vector breeding habitats such as stagnant water sources can help limit the spread of BTV and EHD.
  • Wetland management may also be considered.

Research and Surveillance:

  • Researching the epidemiology and genetics of BTV and EHDV can inform more effective prevention and control strategies, while surveillance should include tracking new virus strains or serotypes that emerge.

Public Awareness and Education:

  • Raising awareness among farmers, ranchers, and the general public about disease transmission vectors and vaccination can encourage proactive measures.

What are the available vaccination options for Blue Tongue and EHD?

Here are a few vaccines commonly used against BTV and EHD:

Blue Tongue Disease (BTV):

  • Modified Live Vaccines (MLV): MLV vaccines contain live Blue Tongue virus strains in an attenuated form for long-lasting immunity in areas endemic for this infection. They are often utilized as preventive measures.
  • Inactivated Vaccines: Inactivated or killed vaccines contain inactivated Blue Tongue virus particles and are considered safe, providing immunity without risking disease transmission.
  • Recombinant Vaccines: Recombinant vaccines are engineered to produce specific viral proteins to induce an immune response against BTV infections and provide targeted protection.
  • Multi-Serotype Vaccines: To provide wider coverage against multiple serotypes of BTV viruses, some vaccines offer multi-serotype coverage.
  • Polyvalent Vaccines: Polyvalent vaccines may combine antigens from different serotypes or strains of the Blue Tongue virus to provide more comprehensive protection.
  • Vector-Based Vaccines: Researchers are exploring novel vaccination approaches using viral vectors to deliver Blue Tongue virus antigens directly.

Epizootic Hemorrhagic Disease (EHD):

  • Inactivated Vaccines: Similar to BTV vaccines, inactivated EHD virus particles have been rendered harmless through inactivation and used as inactivated vaccines against EHD to provide immunity without inducing disease.
  •  MLV Vaccines: Some MLV vaccines have also been developed as an additional method for EHD protection.
  • Polyvalent Vaccines:Polyvalent EHD vaccines may provide protection from multiple strains or serotypes of EHD virus.

Research and Developments in Blue Tongue and EHD Management

Research and innovations regarding Blue Tongue Disease (BTV) and Epizootic Hemorrhagic Disease (EHD) management remain vitally important in safeguarding livestock and wildlife populations against these viral diseases.

As research continues to address Blue Tongue, attention is focused on vaccine development to increase cross-protection against multiple BTV serotypes, thus reducing the need for multiple vaccinations.

Scientists are investigating improved diagnostic methods for early detection and serotype identification; climate impact assessments provide insight into how climate change may influence vector distribution patterns and disease prevalence rates.

EHD research efforts focus on creating effective vaccines for both livestock and wildlife populations, with white-tailed deer as an especially vulnerable species to EHD. Furthermore, wildlife management strategies aim to understand deer movement patterns as well as factors impacting EHD transmission within communities of wildlife.

Both diseases benefit from advances in vector control, with researchers exploring innovative strategies to manage Culicoides midge populations. Diagnostic tools continue to be improved for faster and more accurate detection.

Climate modeling plays an integral part in understanding how climate change may alter disease dynamics and implementing proactive management strategies.

Collaboration among veterinary scientists, entomologists, ecologists, and climatologists is crucial for staying abreast of BTV and EHD’s evolving challenges. Their research efforts contribute to more efficient prevention, control, and management measures aimed at mitigating their effects on both livestock and wildlife populations.


Blue Tongue and Epizootic Hemorrhagic Disease (EHD) are viral infections affecting livestock and wildlife worldwide, impacting domestic as well as wild ruminants alike. Bluetongue virus (BTV) infection causes Blue Tongue which spreads globally impacting domestic as well as wild ruminants alike. Culicoides midges transmit this disease, which manifests with fever and blue tongue discoloration both symptoms that pose economic threats to livestock owners.

EHDV infection mainly impacts North America and is restricted to white-tailed deer herds. EHD manifests with fever, mouth ulcers, and hemorrhaging symptoms transmitted via Culicoides midges. Though both diseases share clinical similarities and transmission via similar vectors; their respective causative agents require different management and prevention strategies.

By admin

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