Equine Infectious Anemia (EIA): Symptoms, Diagnosis, and Prevention

Equine Infectious Anemia (EIA) is a slow virus infection transmitted through the exchange of blood, saliva, or other bodily fluids. The virus targets and destroys red blood cells (RBCs), leading to varying degrees of anemia in affected horses. This disease is endemic in horse populations worldwide. Once infected, horses become lifelong carriers and remain a continuous source of infection. Currently, there is no effective vaccine to combat the virus.

For stable owners and managers aiming to maintain herd health and stable operations, regular testing and isolation of seropositive individuals are fundamental measures for disease control. This article will provide a detailed overview of the clinical manifestations and testing protocols for EIA, giving you a deeper understanding and recognition of Equine Infectious Anemia.

What is Equine Infectious Anemia?

Equine Infectious Anemia (EIA) is caused by a lentivirus belonging to the Retroviridae family. The disease not only compromises the immune system but also causes massive destruction of red blood cells, leading to an anemic state in affected horses. Due to EIA's potentially long incubation period—lasting weeks or even longer—and its varied clinical presentation, early detection is often challenging. Furthermore, the virus remains persistently transmissible while latent in the host, making this disease a matter of serious concern in international equine trade and competition quarantine procedures. To mitigate the risk of EIA dissemination, it is highly recommended that equine facilities establish thorough testing protocols and robust management techniques. This ensures the health of the herd and maintains the stable operation of the premises.

Common Symptoms of Equine Infectious Anemia: A Quick Guide

The clinical signs of Equine Infectious Anemia are largely nonspecific, ranging from mild lethargy and severe hemorrhage to collapse and immune system damage. Relying solely on a horse's physical appearance for diagnosis can easily lead to confusion with other diseases, such as piroplasmosis or leptospirosis, resulting in delayed treatment and misdiagnosis. Beyond daily observation of a horse's body condition and activity level changes, owners are advised to utilize professional veterinary blood tests. This minimizes the risk of diagnostic errors and disease spread. The table below summarizes the common symptoms of EIA, helping owners better identify the various clinical manifestations.

Table of Common Equine Infectious Anemia Symptoms

*The table is scrollable horizontally on mobile.
 

Understanding Equine Infectious Anemia (EIA) Types, Causes, and the Importance of Stable Hygiene

Reliance solely on a horse's physical appearance is insufficient to confirm Equine Infectious Anemia (EIA) infection; it must be correlated with both clinical signs and test results. The following explains the main types of EIA and its sources of infection to help stables formulate correct procedures for epidemic prevention and horse care, thereby reducing the risk of cross-infection within the herd.

Types of Equine Infectious Anemia

EIA can be classified into acute, chronic, and inapparent (or latent) carrier types. The symptoms of these different types are detailed below. Clearly distinguishing the stage and condition of EIA helps veterinarians effectively manage the disease and establish appropriate isolation and management measures.

• Acute EIA: Often seen during the initial infection. It is characterized by a rapid rise in body temperature accompanied by severe anemia, and it has a relatively high mortality rate.
• Chronic EIA: Symptoms include recurrent episodes of fever, lethargy, and weight loss. The course of the disease can last several months.
• Inapparent (Latent) Carrier EIA: The horse appears healthy but still harbors the virus internally. If bitten by blood-sucking insects, it poses a risk of transmitting the virus to other horses in the herd.

Causes of Equine Infectious Anemia

EIA is primarily transmitted through blood, with blood-sucking insects like horse flies and deer flies being the most common vectors. If the stable environment is damp and has many standing water sources, insect breeding accelerates, naturally increasing the risk of infection. Stables are advised to diligently implement environmental disinfection, eliminate standing water, and enforce strict mosquito and fly control to minimize transmission opportunities. In rare instances, the virus may also spread through contaminated needles, surgical instruments, or blood transfusions. Additionally, an infected mare may transmit the virus to her foal during gestation.

Is Equine Infectious Anemia Treatable? Daily Monitoring Cannot Be Overlooked!

Currently, there is no drug or vaccine that can completely treat EIA; infected horses remain lifelong carriers. Therefore, once a horse is confirmed positive, it must be isolated or euthanized according to regulations to prevent the continuous spread of the virus and contain the outbreak. Since the pathogen cannot be cleared once a horse contracts EIA, regular blood testing and vector control are the only ways to prevent and maintain the health of the herd. Early detection can prevent significant losses from spreading throughout the entire facility.

An Overview of the 2 Major EIA Testing Methods

Testing for EIA primarily relies on detecting the antibody response in the blood. Common methods include the Agar Gel Immunodiffusion (AGID) test and the Enzyme-Linked Immunosorbent Assay (ELISA). The former is internationally recognized as the standard diagnostic method, while the latter is often used for initial screening. When necessary, a positive ELISA result must still be confirmed with the AGID test. Using these two methods in conjunction ensures both accuracy and testing efficiency. Their principles and applications are explained below.

Agar Gel Immunodiffusion (AGID) Test

The Agar Gel Immunodiffusion test, commonly known as the Coggins test, involves placing serum and antigen on an agar plate to observe the formation and fusion of a precipitate line. A positive result indicates the horse carries the EIA pathogen; a negative result indicates a healthy individual. A suspicious (or inconclusive) result requires a retest after 21 days, during which time the horse must be isolated to prevent potential disease spread.

Enzyme-Linked Immunosorbent Assay (ELISA)

he Enzyme-Linked Immunosorbent Assay (ELISA) uses an enzyme reaction to determine the presence of EIA antibodies or antigens in the blood. This method is fast and suitable for screening large numbers of horses. However, a positive result still requires confirmation with the AGID test to ensure accuracy.
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SANcheck | StrideVet 4in1 Instantly Helps You Monitor Your Horse's Daily Status!

The SANcheck brand, a subsidiary of General Life Biotechnology, has launched the StrideVet 4in1 Multi-Monitoring System, which can measure Packed Cell Volume (PCV) data. PCV is a crucial index for evaluating the degree of anemia, and anemia is one of the main clinical manifestations of EIA. Veterinarians can use the StrideVet 4in1 to obtain PCV data instantly on-site (the normal PCV range is approximately 12–78%), quickly determining if the horse is at risk for anemia. This provides an important reference for deciding whether to proceed with standard EIA antibody testing (AGID/ELISA).

In addition to PCV, the instrument can measure Lactate, Triglycerides, and Glucose values, which are used to assess the horse's overall metabolic condition. Because many regions lack specialized equine hospitals and diagnoses are often made by veterinarians on-site, using the StrideVet 4in1 provides immediate data, eliminating the process of sending samples to a lab. This allows stables to manage daily health more conveniently and also adds a layer of assurance to the EIA control and prevention procedures.
〈Related Article: Is Your Pet Diabetic? Learn How a Pet Blood Glucose Meter Can Help〉

Conclusion

Equine Infectious Anemia is an incurable chronic disease, and there is currently no vaccine that can fully counteract it; infection results in being a lifelong carrier. Therefore, instead of focusing on treatment after the fact, the greater priority is the daily implementation of insect control and routine blood testing, forming a comprehensive prevention strategy. By incorporating the SANcheck StrideVet 4in1 professional monitoring device, stables can instantly grasp the horse's PCV and health data, minimizing the risk of missing the optimal window for disease control. The SANcheck brand from General Life Biotechnology is dedicated to providing veterinarians with more precise and rapid testing tools. If you wish to improve the efficiency of disease prevention and safeguard the health of your herd, we welcome you to contact us to learn more about our application solutions.

References
Equine Infectious Anemia
Anemia in Horses
Equine Infectious Anemia
馬傳染性貧血，EIA
What Is a Coggins Test?
馬傳染性貧血症檢驗採用免疫擴散反應試驗