What is the Difference Between Blue Tongue and EHD

The key difference between blue tongue and EHD is that blue tongue is a viral disease that primarily affects domestic sheep, cattle, and goats, while EHD is a viral disease that primarily affects white-tailed deer.

Insects are one of the major agents of spreading animal diseases. They are responsible for major losses in livestock. Blue tongue (BT) and Epizootic Hemorrhagic Disease (EHD) are two vector-borne viral diseases caused by closely related orbiviruses of the family Reoviridae. They are hemorrhagic diseases. These diseases occur in sheep, cattle, goats, and whitetail deer. The transmission of both these diseases occurs by biting gnats. They cause similar symptoms, including drooling, fever, runny nose, and swollen muscle. Gnat control is the most effective way of controlling both diseases.

CONTENTS

1. Overview and Key Difference
2. What is Blue Tongue 
3. What is EHD
4. Similarities – Blue Tongue and EHD
5. Blue Tongue vs EHD in Tabular Form
6. Summary – Blue Tongue vs EHD

What is Blue Tongue?

Blue tongue is a viral disease in sheep, cattle, goats, and deer. It is caused by Bluetongue virus and is a non-contagious disease. Hence, it does not spread among animals due to contact. This disease is known as blue tongue due to the observation of the characteristic darkish blue appearance of the tongue in infected animals. Lips and tongue also become very swollen, causing the tongue to stick out from the mouth. This disease is most often seen in sheep and is responsible for severe diseases and death in sheep. In cattle, it is rarely seen and causes reproductive losses. Erosion and ulceration in the muzzle and mouth, edema, hyperemia, vascular congestion, hemorrhage, and tissue infarction are some of the clinical signs of this disease. Some of the complications that lead to death are erosion and ulceration of the nasal and oral cavity, esophagus, and forestomach, and inflammation and fluid accumulation in the lungs, and internal hemorrhages.

Humans do not get blue tongue disease. This disease spreads by biting insects. In order to save animals from blue tongue disease, preventive measures like insect control by destroying insect habitats and the use of insecticides should be taken.

What is EHD?

Epizootic Hemorrhagic Disease (EHD) is a viral disease commonly seen in white tailed deer. It is caused by the EHD virus and can affect all ages of deer. This virus is highly infectious and can cause many fatalities. In fact, EHD is responsible for more than 90 % of morbidity and mortality in white tailed deer. The clinical signs of EHD in deer include fever, weakness, inappetence, excessive salivation, facial oedema, hyperaemia of the conjunctivae and mucous membranes of the oral cavity, coronitis, stomatitis, and excessive salivation. When the disease occurs for a prolonged period, complications such as bloody diarrhoea, haematuria, dehydration, and death can occur.

EHD transmission occurs through the biting of gnats, which are tiny files smaller than mosquitoes. The diagnosis of EHD can be made by virus testing on tissue and blood. The viral testing mainly includes immunofluorescence and reverse transcriptase polymerase chain reaction (RT-PCR) tests. In addition, clinical signs are utilized in the diagnosis of this disease in deer. There is no particular treatment for EHD other than care.

What are the Similarities Between Blue Tongue and EHD?

• Blue tongue and EHD are viral diseases in cattle, sheep, and whitetail deer.
• Both diseases are spread by biting gnats.
• Transmission of both diseases declines in cooler weather.
• Infecting agents of both diseases affect small blood vessels and reduce the blood supply.
• Both diseases can be diagnosed by testing the blood of infected animals.
• There is no effective treatment for both diseases.
• Control of gnats is the most effective way of preventing these diseases.
• The spreading of blood from one animal to the other should be prevented in order to control these diseases among animals.
• There is no risk of blue tongue disease and EHD in humans.

What is the Difference Between Blue Tongue and EHD?

Blue tongue is a viral disease that primarily affects sheep, cattle, and goats, while EHD is a viral disease primarily seen in white tailed deer. Thus, this is the key difference between blue tongue and EHD. Blue tongue is caused by Bluetongue virus, while EHD is caused by Epizootic hemorrhagic disease virus. Furthermore, blue tongue causes reproductive losses in cattle, but EHD in cattle is unusual. Clinical signs of blue tongue disease are erosion and ulceration in the muzzle and mouth, and edema, hyperemia, vascular congestion, hemorrhage, and tissue infarction, while the clinical signs of EHD are fever, weakness, inappetence, excessive salivation, facial oedema, hyperaemia of the conjunctivae and mucous membranes of the oral cavity, stomatitis, and excessive salivation.

The below infographic presents the differences between blue tongue and EHD in tabular form for side-by-side comparison.

Summary – Blue Tongue vs EHD

Blue tongue and EHD are two vector-borne viral diseases affecting livestock animals. Humans are not susceptible to both diseases. Both diseases are transmitted by insect biting. The key difference between blue tongue and EHD is that blue tongue disease is primarily seen in sheep, while EHD is primarily seen in white-tailed deer. Insect control is the most effective way of preventing these diseases. Both diseases are caused by two closely related viruses in the family of Reoviridae.

Reference:

1. Rivera, Nelda A, et al. “Bluetongue and Epizootic Hemorrhagic Disease in the United States of America at the Wildlife-Livestock Interface.” Pathogens (Basel, Switzerland), MDPI, 21 July 2021.
2. “Epizootic Hemorrhagic Disease.” Cornell Wildlife Health Lab, 4 Nov. 2016.

Image Courtesy:

1. “Bluetongue-virus-transmission-by-culicoides” By Alan R Walker – Own work (CC BY-SA 3.0) via Commons Wikimedia