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Equine Protozoal Encephalitis (EPM)– Causes, Prevention, and Management with Acupressure Therapy

Updated: Dec 8, 2023


horse eating grass may pick up EPM from opossum

In the realm of equine health, where every hoofbeat tells a story of strength and vitality, a silent threat looms—a neurological disruptor known as Equine Protozoal Encephalitis (EPM). As horse enthusiasts, caretakers, and riders, understanding the intricacies of EPM becomes paramount, especially when the initial sign of gait abnormality sends shockwaves through the foundation of a horse's graceful movement.


EPM, caused by protozoa infiltrating the central nervous system, manifests its presence through a subtle but unmistakable betrayal—the compromised gait of an afflicted horse. Incoordination and muscle weakness replace the once-fluid movements, signaling the onset of a complex battle within.


This blog aims to demystify EPM, unraveling the layers of this enigmatic disease. From the initial symptoms that herald its presence to the diagnostic challenges faced by veterinarians, we will explore the nuances of this condition. Join us in dissecting Equine Protozoal Encephalitis and gain insights into its management, as we navigate the delicate intersection of equine health and neurological resilience.


Understanding Equine Protozoal Encephalitis

In the intricate world of equine health, Equine Protozoal Encephalitis (EPM) stands out as a complex ailment, drawing attention to the delicate workings of the central nervous system. As an acronym carrying significant implications for our equine partners, EPM presents a distinct and clear initial signal—a noticeable gait abnormality. Rooted in incoordination and muscle weakness, this indicator serves as an undeniable cue, revealing an underlying neurological struggle that warrants careful consideration.

equine protozoal encephalitis under microscope
Photo credit: Texas A&M

Equine Protozoal Encephalitis, initiated by protozoa affecting the central nervous system, subjects horses to a range of physiological challenges. The foremost sign, gait abnormality, serves as a tangible marker of the disruptions unfolding within. Once characterized by graceful movement, the horse now grapples with a compromised ability to walk, prompting a deeper exploration into the intricacies of this enigmatic condition.


In the early stages of EPM, the equine gait, a reflection of seamless muscle coordination, succumbs to disruption. Incoordination and muscle weakness weave an unsettling prelude, transforming the rhythmic cadence of a horse's steps into a discordant symphony of imbalance. Recognizing this initial sign becomes imperative, as it acts as the harbinger of a neurological challenge that necessitates prompt attention.


As we delve deeper into understanding EPM, we navigate the intricate threads of its neurological challenges. Beyond the visible gait abnormalities lie the subtleties of a condition that may impact various facets of the horse's well-being. The interplay of protozoa and the central nervous system beckons us to unravel the layers of this complex ailment, fostering a comprehensive comprehension that extends beyond surface-level symptoms.


Understanding How Horses Contract EPM

EPM is primarily caused by the protozoan Sarcocystis Neurona, with rare instances attributed to Neospora Hughesi. The crucial link in this transmission chain is the opossum, serving as the definitive host that facilitates the spread of the parasitic organism to horses.

  • The Definitive Host: Opossums, ubiquitous in many ecosystems, play a pivotal role in the life cycle of the EPM-causing protozoa. These marsupials acquire the parasite by feeding on intermediate hosts such as cats, armadillos, skunks, and raccoons. Once infected, the opossums become carriers, hosting the protozoa within their system.

  • Transmission Through Feces: The critical point of transmission occurs when horses unwittingly ingest the opossum feces. This can happen during grazing in pastures or while drinking water contaminated with opossum droppings. The protozoa, present in the feces in the form of sporocysts, find their way into the equine system through ingestion.

  • Intermediate Hosts: Cats, armadillos, skunks, and raccoons, acting as intermediate hosts, serve as carriers for the protozoa. These animals become part of the intricate transmission cycle by hosting the parasitic organism in their tissues, contributing to the perpetuation of the disease in the environment.

  • Invasion of the Central Nervous System: Once inside the equine host, the protozoa make a formidable journey. The sporocysts, having crossed the blood-brain barrier, target the central nervous system, specifically the brain and spinal cord. This invasion marks the onset of EPM, as the protozoa wreak havoc within the neurological architecture of the horse.

  • Exclusive Transmission via Opossums: It's noteworthy that horses contract EPM exclusively through opossums and not through other hosts in the transmission cycle. The unique relationship between the protozoa, the opossum, and the equine host highlights the specificity of this parasitic affliction.

In comprehending the intricate pathways through which horses develop EPM, we gain insights into the ecological choreography that underlies the transmission of this parasitic disease. Join us as we unravel the complexities of this equine health challenge, exploring the multifaceted interactions between hosts and parasites that shape the landscape of EPM transmission..

life cycle of EMP in horses and other animals
Photo credit: Semantic Scholar


Which Horses are More Susceptible to EPM

In the intricate landscape of equine health, the risk of contracting Equine Protozoal Encephalitis (EPM) is not uniform across all horses. Instead, a nuanced interplay of geographical, environmental, and individual factors shapes the susceptibility of equines to this parasitic affliction. Delving into these intricacies provides a comprehensive understanding of the horses that stand at a higher risk of succumbing to EPM.

opossum could have EPM

Geographical Factors

The prevalence of EPM is closely tied to the distribution of opossums, the definitive host in the transmission cycle. Horses residing in areas with high opossum populations face an elevated risk of exposure to the parasite. Regions characterized by warm and humid climates, such as the southeast of the United States, often harbor larger opossum populations, intensifying the likelihood of EPM transmission. It's crucial to recognize that opossums can be present in various locations, emphasizing the need for awareness regardless of geographic location.


Prevalence and Antibodies

Studies estimate that a substantial percentage of horses, ranging between 50% to 90%, carry antibodies for Sarcocystis neurona, the causative protozoan. However, only a minute fraction—approximately 1%—of these horses display clinical signs of EPM. This discrepancy highlights the complex dynamics between exposure and manifestation, underlining the importance of exploring individual risk factors.


Breeds and Age

Certain equine demographics are more susceptible to EPM. Breeds at greater risk include standardbreds, Warmbloods, Thoroughbreds, and stallions. Among age groups, younger horses, particularly males, are more prone to the disease. Understanding these predispositions allows for targeted preventive measures and vigilant monitoring in high-risk populations.


Seasonal Vulnerability

The risk of EPM peaks during the spring and summer seasons. The warmer weather creates an environment conducive to the survival and transmission of the protozoa, amplifying the chances of horses encountering the infectious sporocysts.


In unraveling the factors that contribute to the susceptibility of horses to EPM, we gain insights into the nuanced interplay of environmental, individual, and seasonal elements. Join us as we navigate through the intricacies of equine vulnerability, fostering a deeper understanding of the risks that shape the prevalence of Equine Protozoal Encephalitis in diverse equine populations.


Signs and Symptoms of EPM

Equine Protozoal Encephalitis (EPM), a stealthy assailant of the central nervous system, reveals its presence through a nuanced tapestry of signs and symptoms. The initial indicators materialize on the head, progressively extending their grip over the rest of the body as the disease takes hold. In this exploration, we delve into the common manifestations that define the spectrum of EPM, from mild hints to more severe neurological challenges.


The first whispers of EPM emerge on the head, serving as a poignant prelude to the broader neurological turmoil that unfolds later. Ataxia, muscle atrophy, and asymmetry, where one side of the body displays more signs than the other, set the stage for the gradual progression of symptoms. As the disease tightens its grip, the body becomes a canvas on which EPM paints its distinctive portrait.


Let's have a look at some common signs and symptoms of EPM:

horse showing signs of EMP hind end weakness
Photo credit: Ride on St. Louis
  • Facial Paralysis: A telltale sign of EPM is the onset of facial paralysis, manifesting as a lack of mobility or expression on one side of the face.

  • Head Tilt: An observable tilt of the head to one side indicates the neurological impact of EPM, a subtle but distinct marker of the disease.

  • Droopy Lip and Ear: EPM often manifests as a droopy lip or ear, further signaling the disruption in the intricate coordination of facial muscles.

  • Muscle Twitch: Uncontrollable muscle twitches serve as a visual cue, reflecting the underlying neurological disturbance.

  • Swallowing Difficulties: Horses afflicted by EPM may experience difficulty in swallowing, leading to notable changes in their eating behavior.

  • Incoordination or Ataxia: A hallmark of EPM, incoordination or ataxia becomes apparent in the horse's movements, disrupting its once-fluid gait.

  • Abnormal Gait on Slopes: The impact of EPM becomes pronounced when horses display an abnormal gait, particularly when traversing slopes or uneven terrain.

  • Poor Balance and Stall Leaning: Horses may struggle with balance, often leaning on stall walls for support, showcasing the neurological challenges they face.

  • Pelvic Sway: A noticeable sway in the pelvic region underscores the pervasive effects of EPM on the horse's musculoskeletal system.

  • Weakness in Hind End: Progressive weakness in the hind end becomes evident, compromising the horse's ability to move with its customary strength and agility.

  • Lameness: EPM may culminate in lameness, a tangible expression of the toll exacted on the horse's overall mobility and well-being.


Dispelling Misconceptions: The Non-Contagious Nature of EPM

Contrary to some common misconceptions, EPM is not a contagious disease. Horses afflicted by this condition do not serve as vectors for transmitting the causative protozoa to their equine counterparts. The horse, in this context, is what is known as a "dead-end host" to the protozoa responsible for EPM. While horses can indeed become infected, they cannot act as carriers capable of spreading the disease to others.


As a dead-end host, a horse can acquire the infection, but the life cycle of the protozoa within the horse does not involve transmission to other hosts. This breaks the cycle of contagion within equine populations, alleviating concerns of EPM spreading like a communicable ailment among horses.


Further debunking any lingering concerns, it's crucial to emphasize that EPM is specific to horses and does not pose a threat to other animals. The protozoa responsible for EPM are not transferable to different species, dispelling the notion that the disease might cross over to other domestic or wild animals.


Assessing and Confirming EPM in Horses

The elusive nature of Equine Protozoal Encephalitis (EPM) poses a considerable diagnostic challenge for veterinarians. Unlike some ailments that yield to a straightforward diagnostic test, EPM necessitates a comprehensive approach involving a careful examination of clinical signs, historical context, and, when required, specialized tests. In this exploration, we unveil the nuanced diagnostic journey undertaken by veterinarians to assess and confirm the presence of EPM in horses.


Clinical Evaluation and Neurological Signs

The diagnosis of EPM commences with a thorough physical examination and an in-depth exploration of the horse's medical history. A skilled veterinarian scrutinizes neurologic signs, emphasizing key indicators such as incoordination, loss of sensation, muscle paralysis, and loss of balance. One of the distinctive features is the asymmetry of these signs, with one side of the horse's body more affected than the other. Notably, manifestations may include muscle weakness and atrophy on one side, providing crucial diagnostic clues.

horse with EPM getting vet exam
Equine neurologic exams help determine if the horse is balanced and has the ability to function on all legs properly. Photo credit: Platinum Performance

Blood Tests and Antibody Detection

While no single diagnostic test exists for EPM, blood tests are often recommended to assess the presence of specific antibodies. These tests, however, do not definitively rule out infection. Antibodies for Sarcocystis neurona and Neospora hughesi are detected in the blood, indicating exposure rather than the current status of the disease. Titer exams, available through institutions like UC Davis, can provide insights into the likelihood of active disease, while IgM tests confirm the current presence of EPM.


Cerebrospinal Fluid (CSF) Analysis

For a more definitive diagnosis, analysis of cerebrospinal fluid (CSF) emerges as a critical protocol. Veterinarians can perform this procedure through spinal tapping, collecting fluid from either the head or hip region. While the head region requires general anesthesia, tapping from the hip region is preferable due to its less invasive nature. CSF analysis allows for the detection of antibodies after blood tests and offers valuable insights into the active state of the disease.


Titer Exams

UC Davis offers specialized titer exams that contribute to determining the likelihood of the horse currently having the disease. These exams provide a nuanced perspective, aiding veterinarians in confirming and understanding the dynamics of EPM in the individual horse.


Differential Diagnosis

The diagnosis is usually difficult as it mimics other neurological diseases, including Rabies, Equine Encephalitis, Lyme Disease, West Nile Virus, Equine Herpesvirus 1, Selenium deficiency or toxicity, and Cushing’s disease.


In summary, the diagnosis of EPM involves a multifaceted approach, combining clinical observation, blood tests, and, when necessary, cerebrospinal fluid analysis. This comprehensive strategy enables veterinarians to navigate the diagnostic puzzle of Equine Protozoal Encephalitis, paving the way for informed treatment decisions and tailored care for affected horses.


Strategies for Preventing Equine Protozoal Encephalitis (EPM)

Equine Protozoal Encephalitis (EPM) poses a distinct challenge in terms of prevention, with its primary mode of transmission linked to opossum feces. Mitigating the risk of this neurological affliction requires a strategic approach that focuses on controlling opossum presence and minimizing the opportunities for transmission. In this comprehensive guide, we delve into practical and effective measures aimed at safeguarding horses against the threat of EPM.


Controlling Opossum Access

  • Natural Deterrents: Employing natural deterrents such as garlic, onions, or mothballs serves as an initial line of defense against opossum intrusion. These substances emit odors that deter opossums, helping to create a protective barrier around the horse environment.

  • Secure Feed and Bedding Areas: Erecting barriers to keep opossums out of feed and bedding areas is imperative. Whether through the installation of fences or other protective measures, minimizing access to these crucial spaces reduces the risk of contamination.

  • Covered Feed and Water Containers: Opossums are drawn to horse feed, making it crucial to keep feed and water containers covered or sealed. This not only prevents contamination but also reduces the likelihood of attracting opossums to feeding areas.

  • Bird Food and Spilled Grains: Vigilance in maintaining a clean environment is paramount. Discourage the presence of opossum attractants by ensuring there is no bird food left in the horse feed area. Additionally, promptly clean up fallen fruit or spilled grains to minimize potential food sources for opossums.

Optimizing Feed Handling

  • Stored Bulk Feed and Steamed Hay: Opting for stored bulk feed minimizes the risk of contamination, as opposed to exposed bags that may attract opossums. Additionally, steaming hay is an effective measure to eliminate parasites, contributing to a more controlled and hygienic feeding environment.

  • Protective Fencing: Installing fences or wires serves as a physical deterrent to prevent opossum raids on feed areas. This proactive measure reinforces the containment of the horse environment and reduces the likelihood of opossum intrusion.


Prompt Disposal of Deceased Animals

  • Dispose of Dead Animals: Swiftly disposing of any deceased animals in the area is crucial, as opossums may be attracted to feed on them. Timely removal of carcasses eliminates potential sources of infection and reduces the risk of opossum-borne diseases.

By integrating these preventive strategies into equine management practices, horse caretakers can take significant steps toward fortifying the health and well-being of their equine companions, minimizing the risk of Equine Protozoal Encephalitis.


Comprehensive Management Strategies for EPM

Equine Protozoal Encephalitis (EPM) poses a significant threat to the neurological well-being of horses, with the potential for severe complications and permanent brain damage if left untreated. Early and proactive management becomes paramount in mitigating the impact of this condition. In this comprehensive guide, we explore multifaceted strategies encompassing medication and diet management to safeguard the health of horses afflicted by EPM.


Recognizing the urgency of EPM management is crucial, as the consequences of untreated cases can lead to irreversible damage to the horse's brain. Early intervention becomes a pivotal factor in mitigating the progression of the disease and preserving the neurological health of the horse.


Medication: Antibiotics as a Cornerstone of Treatment

  • FDA-Approved Antibiotics: A cornerstone of EPM management involves the use of FDA-approved antibiotics to target the causative protozoa. Three primary antibiotics come into focus: ponazuril, diclazuril, and sulfadiazine.

  • Ponazuril and Combination Therapies: Ponazuril, often the preferred choice, works by inhibiting the replication of parasites, thereby reducing their numbers. In certain cases, a combination of antibiotics may be recommended, enhancing the efficacy of treatment.

Diet Management: Nourishing the Neurological System

  • Vitamin E Supplementation: Integrating vitamin E supplements into the horse's diet proves beneficial in managing EPM. Acting as antioxidants, these supplements contribute to the strengthening of the immune system and facilitate the healing of nerve tissue. Crucially, they play a role in preventing permanent brain damage.

  • Selenium Intake: Selenium deficiency can exacerbate issues in the nervous system. Managing selenium intake becomes essential, ensuring that the horse receives an adequate supply of this crucial element for neurological health.

  • Natural Feed Sources: Opting for a natural and balanced diet is instrumental in supporting the overall health of the horse. Incorporate grass forage and herbs such as nettle, dandelion, feverfew, and ginseng into the diet. Avoid grains and processed feed, focusing on nourishing the horse with wholesome, natural nutrition.


The Role of Acupressure Therapy in EPM Prevention and Complementary Care

In the realm of equine health, where preventive measures and complementary therapies play a pivotal role, acupressure therapy emerges as a valuable tool in the prevention and management of Equine Protozoal Encephalitis (EPM). This ancient practice, rooted in the principles of traditional Chinese medicine, offers a holistic approach to fortifying the immune system, alleviating stress, and providing complementary relief for horses affected by EPM.


The Link Between Acupressure and EPM Prevention

  • Stress Reduction and Immune Strengthening: Acupressure therapy, when incorporated into a horse's routine, serves as a proactive measure for preventing EPM. Regular sessions are known to alleviate stress and bolster the immune system, addressing one of the primary factors that make horses susceptible to EPM—the weakening of the immune defenses. A robust immune system acts as a natural barrier against the protozoa responsible for EPM, preventing the onset of the disease.

  • Immune System Resilience: Horses exposed to the EPM-causing parasite may not necessarily contract the disease if their immune systems are robust. Acupressure, through its gentle pressure techniques applied to specific acupoints, contributes to the overall resilience of the immune system. This proactive approach may potentially reduce the likelihood of horses succumbing to the invader, emphasizing the preventive role of acupressure in EPM management.


Complementary Benefits for Horses Displaying Signs of EPM

  • Muscle Relaxation and Ataxia Reduction: In cases where horses exhibit signs of EPM, acupressure therapy becomes a complementary tool in managing symptoms. The gentle yet targeted application of pressure on specific acupoints helps relax muscles and may aid in reducing ataxia—the hallmark sign of EPM characterized by incoordination. By promoting relaxation and easing muscle tension, acupressure contributes to the overall well-being and comfort of the affected horse.


Integration into Holistic Equine Care

  • Comprehensive Wellness: Acupressure therapy, as part of a holistic equine care regimen, aligns with the philosophy of addressing not only the symptoms but also the underlying imbalances within the horse's body. Its non-invasive nature and adaptability make it a versatile and well-received component of a comprehensive wellness plan.

  • Consultation with Equine Health Professionals: While acupressure therapy offers notable benefits, it is essential to integrate it under the guidance of equine health professionals. Consultation with veterinarians and qualified practitioners ensures that acupressure is tailored to the specific needs of the horse, considering its overall health status and any ongoing treatments.

In embracing the gentle yet powerful touch of acupressure therapy, horse caretakers can proactively contribute to EPM prevention and provide supportive care for those affected by this complex neurological condition. The synergy between traditional healing practices and modern equine health management underscores the potential for a more integrated and balanced approach to the well-being of our equine companions.








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