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What You Should Know About Equine Infectious Anemia (EIA)

Updated: Dec 8, 2023


Horses in pasture are at risk for Equine Infectious Anemia

Do you know a horse once infected with Equine Infectious Anemia it becomes a carrier for their lifetime? That's why it is best to prevent this vicious disease. But for that, you must know facts about this disease and how to protect your horse from it. In this blog post, we will discuss what you need to know about Equine Infectious Anemia in horses, including the symptoms, prevention methods, and supportive treatments available.


What is Equine Infectious Anemia?

Equine Infectious Anemia (EIA) is a significant health concern among horses, donkeys, and mules, caused by the equine infectious anemia virus (EIAV). This viral disease primarily spreads through the exchange of bodily fluids, particularly blood, and is known to be transmitted by blood-feeding insects such as horseflies and deerflies. Additionally, EIAV can be transmitted from an infected mother to her foal during gestation.


It's important to note that EIA is not directly contagious between horses through casual contact. Instead, the virus requires a more specific mode of transmission, such as blood-to-blood contact. This can occur through insect bites or the sharing of contaminated medical equipment, including needles and syringes.


The clinical manifestations of EIA in infected horses are diverse and can range from mild to severe. Common symptoms include fever, lethargy, loss of appetite, weight loss, and the enlargement of lymph nodes. In more severe cases, affected horses may exhibit jaundice, a condition characterized by yellowing of the mucous membranes and skin due to liver dysfunction. Anemia, a decrease in red blood cell count, is another potential consequence of EIA and can contribute to the overall debilitation of the infected animal.


One of the challenges with EIA is that infected horses can become carriers of the virus, serving as a potential reservoir for its spread. Consequently, preventing EIA often involves monitoring, particularly in regions where the disease is prevalent. Testing methods typically involve detecting antibodies or the viral genetic material in the blood.


Due to the potential severity of the disease and its impact on the equine population, various countries implement control measures, such as mandatory testing and strict biosecurity protocols. These measures are crucial for preventing the further spread of EIA and safeguarding the health of equine populations.


Development and Transmission of Equine Infectious Anemia (EIA): Mechanisms and Modes of Spread

horsefly and deer fly comparison
Photo credit: pbsanimalhealth

Equine Infectious Anemia (EIA) develops in horses primarily due to infection with the Lentivirus, specifically the Equine Infectious Anemia Virus (EIAV). The virus is predominantly transmitted through the bite of blood-feeding insects, particularly horseflies and deerflies. This mechanical mode of transmission occurs when an infected insect deposits the virus-laden saliva into the horse's skin while feeding on its blood.


While insect bites are a common natural route of transmission, EIA can also be spread through various other means. One significant mode of transmission is through blood transfusions. If an EIA-positive horse's blood is transferred to another horse, either intentionally or accidentally, it can result in the recipient horse becoming infected. However, in the US, blood transfusions are not common.


The sharing of contaminated needles, syringes, or other medical tools is another common avenue for EIA transmission. This can happen during medical procedures or when horse owners use the same equipment on multiple animals without proper sterilization. Contaminated surfaces, especially metal ones, can harbor the virus, contributing to its persistence in the environment.


Breeding with an infected horse, especially one that is a carrier of the virus, poses a risk of transmission from the dam to the foal. Additionally, EIAV can be transmitted from a pregnant mare to her foal through the colostrum and milk, providing another route of vertical transmission.


An interesting aspect of EIA is its ability to remain dormant in an infected horse for an extended period without causing noticeable signs of illness. This latent or chronic carrier state allows the virus to persist in equine populations, posing a challenge for disease control and management efforts.


Overall, the diverse modes of transmission highlight the complexity of preventing and controlling EIA. Rigorous biosecurity measures, regular testing, and responsible management practices are essential to minimizing the risk of EIA transmission and maintaining the health of equine populations.


Clinical Manifestations of Equine Infectious Anemia (EIA): Varied Symptoms and Severity

Equine Infectious Anemia (EIA) manifests with a spectrum of signs and symptoms that can vary widely among infected horses, depending on their individual immune responses. It is noteworthy that a significant portion of infected horses may not display any visible signs, making detection and control challenging.


For horses that do exhibit symptoms, the clinical presentation can range from mild to severe. Some common signs of EIA include:

horse with jaundice from EIA
Jaundice can be seen on the mucous membranes in the mouth. Photo credit: Leg Up Equine Veterinary Services
  • Fever: Infected horses often experience an elevated body temperature as a response to the viral invasion.

  • Depression: A general sense of lethargy, fatigue, and decreased interest in surroundings can be observed in affected horses.

  • Weight Loss: Progressive and unexplained weight loss may occur as the virus impacts the horse's overall health and well-being.

  • Muscle Weakness: EIA can lead to muscle weakness, contributing to a reduction in the horse's physical performance.

  • Jaundice: The presence of jaundice, indicated by a yellowish discoloration of the skin, mucous membranes, and eyes, is a possible manifestation of severe EIA, reflecting liver dysfunction.

  • Anorexia/Loss of Appetite: Infected horses may exhibit a reduced desire to eat, leading to a decline in nutritional intake.

  • Edema: Swelling of legs or other body parts due to fluid accumulation may occur, contributing to the overall debilitation of the animal.

  • Frequent Infections and Abscesses: The compromised immune system of EIA-infected horses makes them susceptible to frequent infections and the development of abscesses.

  • Low Red Blood Cells and Platelet Count: EIA can cause a decrease in red blood cell count (anemia) and platelet count, leading to impaired blood clotting.

  • Lymph Node Enlargement: Swelling of lymph nodes may be observed as the immune system responds to the viral infection.

In more severe cases, horses may develop additional complications such as:

  • Cardiomyopathy: Damage to the heart muscle, impacting cardiac function.

  •  Heaves: Chronic pulmonary disease affecting the respiratory system.

  • Neurological Signs: Muscle twitching, weakness, and paralysis may occur, reflecting damage to the nervous system.

It's important to note that the severity of symptoms can vary, and approximately 50% of infected horses may succumb to the disease. Due to the wide range of clinical presentations and potential severity of the disease, early detection through testing and stringent biosecurity measures are crucial for managing and preventing the spread of Equine Infectious Anemia.


Diagnosing Equine Infectious Anemia

The disease can be determined by observing the symptoms in the horse. However, the diagnosis is only confirmed by a vet through blood tests. These tests look for antibodies to the virus that causes EIA, which is present in the blood of an infected horse. To obtain a blood sample, a veterinarian will draw blood from the jugular vein in the neck of the horse. The sample is then sent to a laboratory for testing.


equine coggins test paperwork example showing EIA test results.
Photo credit: Bloom Racing Stable

The gold standard for EIA diagnosis is the Coggins test, which can detect antibodies to the virus up to 8 months after infection. Since most horses do not show symptoms, it is recommended that horses be tested for EIA every 6 months to a year.


Another test used to diagnose EIA is the competitive ELISA test, which detects antibodies of the virus up to 3 months after infection. This test can be done onsite by veterinarians, making it more convenient and cost-effective than the Coggins test.


In some cases, if a horse is showing signs of infection, a veterinarian may opt to perform an Immunofluorescence Assay (IFA) test. This test uses a fluorescent dye to detect antibodies in a horse’s blood and can provide results in a few hours.


If either of these tests comes back positive, the horse should be retested and quarantined until two negative tests have been obtained. The next couple paragraphs will explain the options if the horse tests positive.


Treatment for Equine Infectious Anemia

Equine Infectious Anemia (EIA) poses a significant challenge in terms of treatment, as there is currently no cure for the disease. Once a horse is infected, it becomes a lifelong carrier of the Equine Infectious Anemia Virus (EIAV), and the primary focus shifts to managing the condition and preventing further transmission.


The key approach to managing EIA involves strict isolation or quarantine measures. Infected horses must be kept permanently separated from non-infected individuals in a highly regulated area to prevent the spread of the virus. In some cases, euthanasia may be considered, especially if the horse is suffering, recovery is deemed impossible or strict quarantine is not possible.


While there is no direct antiviral treatment for EIA, supportive care is provided to alleviate clinical signs and prevent complications. Common supportive measures include:

a pony getting blood transfusion treatment for equine infectious anemia
Photo credit: Redwings Horse Sanctuary

  • Systemic Antibiotics: Administered to treat secondary bacterial infections that may arise due to the compromised immune system. Although antibiotics can help reduce the overall viral load, they do not eliminate the virus.

  • Corticosteroids: Used to reduce inflammation and manage symptoms. Corticosteroids can contribute to minimizing the severity of clinical signs.

  • Blood Transfusions: In severe cases where horses are highly anemic, a blood transfusion may be considered to replace lost red blood cells. However, this procedure is rare due to the associated risks of adverse reactions and the logistical challenge of finding a compatible donor horse for each transfusion.

  • Nutritional Support: Horses with EIA may experience weight loss and muscle wasting. Providing nutritional support becomes crucial to maintaining the overall health of the infected animal.

Despite these supportive measures, it is important to emphasize that they do not constitute a cure for EIA. The goal is to manage symptoms, enhance the horse's well-being, and prevent complications. Permanent restriction from various activities, including breeding and competitive events, is necessary to minimize the risk of transmitting the virus to other horses.


Given the lack of a definitive treatment, prevention strategies become paramount. Regular testing, strict biosecurity protocols, and responsible management practices are crucial to controlling the spread of EIA and maintaining the health of equine populations.


Preventing Equine Infectious Anemia

EIA is a serious and life-threatening illness for horses and it can also cause economic losses due to treatment costs and quarantine restrictions. That’s why it’s important to take preventative measures to reduce the chances of your horse getting the disease. Regular testing of all horses on the property, as well as biosecurity protocols such as insect control and eliminating needle sharing, are key in preventing the spread of this disease.


The best way to protect your horse from this disease is to practice good biosecurity. Below are a some best practices that can help reduce the risk of infection:

  • Avoiding contact with untested horses

  • Keeping manure levels low to reduce flies

  • Provide your horse with fly spray, fly masks or fly sheets

  • Prevent overcrowding of animals in pastures or corrals

  • Limit the amount of contact your horse has with other animals, especially those that could carry the virus

  • Make sure to quarantine any new horse

  • Have your horse tested regularly

  • Clean areas in your barn that may attract flies

  • Providing fans in stalls can help flies keep flies off your horse

  • Regular parasite control (dewormers, clean water troughs, manure etc.)

  • Clean your horses stall daily when in use

Vaccines are available but they are not approved in the United States and are not considered a guarantee of immunity.

horse barn cleaning to reduce waste and flies that can carry EIA

Seasonal Patterns in Equine Infectious Anemia (EIA) Transmission: Heightened Risk in Warmer Months

Equine Infectious Anemia (EIA) exhibits a notable seasonal pattern, with a higher likelihood of transmission during warmer months, particularly peaking in July and August. The increased prevalence during these months is attributed to the heightened activity of horseflies, which are known vectors for the Equine Infectious Anemia Virus (EIAV).


Horseflies, including species such as Tabanus and Chrysops, are more active in warmer temperatures, creating conducive conditions for the spread of EIA. These blood-feeding insects play a crucial role in the mechanical transmission of the virus, as they can pick up the virus from an infected horse and transmit it to another horse during subsequent blood meals.


To mitigate the risk of EIA transmission, horse owners are advised to take precautions during the period from May to September, encompassing the warmer months. Implementing effective pest and fly control measures becomes essential to protect horses from potential exposure to infected horseflies. Strategies may include the use of insect repellents, fly masks, and environmental control methods to minimize the presence of horseflies in the vicinity of horses.


By being proactive and implementing preventive measures during the peak transmission months, horse owners can significantly reduce the risk of their animals contracting Equine Infectious Anemia. These efforts contribute to the overall well-being of equine populations and help in maintaining a healthier and disease-free environment for horses.


Can Humans Contract Equine Infectious Anemia (EIA) from Horses? Dispelling Misconceptions

Equine Infectious Anemia (EIA) is exclusively caused by the Equine Infectious Anemia Virus (EIAV), affecting horses, donkeys, and mules. It is important to understand that humans cannot contract EIA from their horses. The virus is highly species-specific, and there is no documented evidence of transmission to humans or other animals.


The primary mode of EIA transmission is through the exchange of bodily fluids, particularly blood, and it occurs primarily via blood-feeding insects such as horseflies and deerflies. While humans are not susceptible to EIA, it is essential to recognize the potential role humans can inadvertently play in the transmission cycle.


Humans can act as mechanical carriers of the virus, unintentionally transferring it from an infected horse to a healthy one through shared equipment or objects. To mitigate this risk, horse owners should adopt precautionary measures:

  • Hand and Equipment Hygiene: Thoroughly wash hands after handling each horse, especially if moving from an infected to a healthy animal. Cleaning and disinfecting equipment, including tack, between horses is crucial.

  • Dedicated Equipment: Use a dedicated set of tack for each horse to prevent cross-contamination. Avoid sharing equipment between horses, particularly if one is known to be infected.

  • Proper Disposal: Dispose of used syringes, needles, or other medical equipment in a safe and responsible manner to prevent accidental transmission.

By incorporating these practices into routine horse care, owners can significantly reduce the risk of inadvertently spreading the virus between horses. While the focus remains on protecting equine health, these measures also underscore the importance of responsible ownership and biosecurity in preventing the unintentional transfer of pathogens between animals.


Acupressure Therapy as Supportive Care for Equine Infectious Anemia: Enhancing Well-being and Connection

Given the untreatable nature of Equine Infectious Anemia (EIA) and the limited scope of supportive treatment, some horse owners explore complementary therapies like acupressure to help support the immune system and overall bodily functions in infected horses. While acupressure does not offer a cure for EIA, it is considered a holistic approach to maintaining the horse's well-being.

equine acupressure practitioner doing bodywork on horse to prevent EIA

The primary goal of acupressure in the context of EIA is to aid the body in sustaining its functions, promoting balance, and potentially alleviating some symptoms associated with the disease. Acupressure involves applying manual pressure to specific points on the horse's body, which are believed to correspond to energy channels and vital organs. By stimulating these points, practitioners aim to facilitate the flow of energy, or "qi," and encourage the body's natural healing processes.


It is crucial to emphasize that acupressure is not a substitute for regular veterinary care. Veterinary professionals play a central role in managing EIA, providing necessary diagnostics, monitoring, and guidance. Acupressure serves as a complementary and supportive therapy, enhancing the overall care plan for the horse.


When used as a preventative measure, acupressure can contribute to the horse's well-being. Regular sessions may help boost the immune system, invigorate blood circulation, regulate body functions, and promote a sense of balance. Integrating acupressure into the daily routine with a horse can establish a positive ritual that fosters a deeper connection between the horse and its caretaker.


The benefits of acupressure extend beyond physical well-being; it also provides an opportunity for horse owners to connect with their animals on a more profound level. The hands-on nature of acupressure fosters a sense of trust and understanding between the horse and its handler, creating a positive and calming experience.



In conclusion, while acupressure therapy offers a holistic approach to supporting horses with EIA, it is essential to approach it as a complementary component of a comprehensive care plan. Collaborating with veterinary professionals and incorporating acupressure into the daily routine can contribute to the overall well-being of the horse, both physically and emotionally.


horse in pasture could get bit by a fly carrying EIA


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