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Leishmaniasis in horses is a parasitic infection caused by Leishmania protozoa and transmitted primarily through the bites of infected sandflies. Although the disease is more common in humans and dogs, horses can also contract infections in regions where these parasites are established in the fly population (endemic). [1][2][3]
Most cases of equine leishmaniasis affect the skin, causing firm nodules, ulcers, crusting, scaling, swelling, or hair loss. These lesions are often localized but can resemble other equine skin conditions.
Leishmaniasis is uncommon in horses and rarely causes systemic illness in equines. However, affected horses may still require treatment to resolve skin lesions, support healing, and monitor for recurrence.
Understanding the signs, causes, diagnosis, treatment, and prevention of leishmaniasis can help horse owners recognize suspicious skin changes and seek appropriate veterinary care.
Keep reading to learn more about how leishmaniasis develops in horses, what clinical signs to watch for, and how veterinarians diagnose and manage this disease.
What is Leishmaniasis?
Leishmaniasis is a vector-borne disease caused by parasites of the Leishmania genus. The disease affects humans and a variety of animal species worldwide and is transmitted through the bites of infected sandflies. [4][5]
Although horses are at risk of infection, they are considered incidental hosts and are affected far less frequently than dogs and humans. Most reported equine cases involve localized skin lesions, while systemic disease is uncommon. [6][7]
Unlike some infectious diseases, leishmaniasis is not spread through direct contact between horses. Instead, infection occurs when a horse is bitten by an infected sandfly.
Several Leishmania species have been identified in horses, including L. infantum and L. braziliensis. Equine leishmaniasis has been reported in Europe, North and South America, Africa, and Asia, particularly in regions where environmental conditions support sandfly populations. [8][9]
Table 1. Leishmaniasis in horses at-a-glance
| Category | Key Information |
|---|---|
| Definition |
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| Primary Cause |
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| Risk Factors |
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| Onset |
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| Symptoms |
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| Severity |
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| Treatment |
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| Recovery Time |
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| Prognosis |
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| Prevention |
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Symptoms of Leishmaniasis in Horses
Clinical signs of leishmaniasis in horses vary depending on the Leishmania species involved and the horse’s immune response.
Most reported cases involve localized skin lesions, though the most common clinical sign is the development of one or more firm skin nodules. These lesions are often found on the head, ears, neck, limbs, or genital region and may be mistaken for other dermatologic conditions. [3][10]
As the disease progresses, nodules may become ulcerated, crusted, or hairless. Some horses develop localized swelling and inflammation around affected areas, although lesions are often not painful and may not cause significant irritation. [3][10]
The primary signs of leishmaniasis in horses include: [1][3][10]
- Firm skin nodules
- Ulcerated skin lesions
- Crusting and scaling
- Hair loss around affected areas
- Localized swelling
- Skin inflammation
Rarely, horses with severe parasite burdens may develop more widespread, whole-body (systemic) disease. Signs of systemic disease may include: [3][10]
Because these signs can resemble several other equine skin disorders, veterinary evaluation and diagnostic testing are required to confirm a diagnosis.
What's your top priority with your horse's health?
What's your top priority with your horse's health?
When to Call the Veterinarian
Horse owners should contact a veterinarian if they notice unexplained skin nodules, ulcers, crusting, or areas of hair loss. Because leishmaniasis can resemble several other equine skin conditions, including sarcoids and squamous cell carcinoma, veterinary evaluation is needed to determine the underlying cause.
Prompt veterinary attention is especially important if skin lesions:
- Increase in size
- Become ulcerated or painful
- Appear in multiple locations
- Fail to respond to routine care
- Develop after travel to an endemic region
Horses living in or traveling to regions where leishmaniasis is endemic may be at greater risk of infection and should be evaluated if suspicious lesions develop. Early diagnosis can help guide appropriate treatment and may improve outcomes by allowing lesions to be addressed before they become more extensive.
Causes of Leishmaniasis in Horses
Horses develop leishmaniasis after exposure to Leishmania parasites transmitted by infected sandflies. The disease is spread by infected female sandflies, which act as vectors and transmit the parasite between susceptible hosts.
Transmission
Sandflies acquire Leishmania parasites while feeding on infected animals. During subsequent blood meals, the parasites can be transmitted to new hosts through the insect’s bite. [4][5]
Once inside the horse’s body, the parasites invade immune cells called macrophages, where they can survive and multiply. This triggers an inflammatory response that may result in nodules, ulcers, and other skin lesions. In most horses, infection remains localized to the skin rather than spreading throughout the body. [3][11][12]
Life Cycle of Leishmania spp.
Leishmania parasites have a two-host life cycle involving a sandfly vector and a mammalian host. The parasite changes form depending on whether it is inside the sandfly or inside the infected animal.
Inside the sandfly, Leishmania exists as a flagellated form called a promastigote. When an infected female sandfly takes a blood meal, it deposits infective promastigotes into the skin at the bite site. [4]
Once in the horse’s skin, the promastigotes are taken up by immune cells called macrophages. Inside these cells, the parasites transform into amastigotes, which are the tissue stage of the parasite. Amastigotes can survive and multiply within macrophages and may spread to other immune cells. [4]
The cycle continues when another female sandfly feeds on an infected host and ingests cells containing amastigotes. Inside the sandfly’s gut, the amastigotes transform back into promastigotes, multiply, develop, and migrate toward the insect’s feeding structures. The sandfly can then transmit the parasite during a later blood meal. [4]
Horses are considered incidental hosts, meaning they can become infected but are not the main reservoir species maintaining the parasite in endemic regions. In horses, reported disease is most often cutaneous and localized rather than systemic.
Risk Factors for Leishmaniasis in Horses
The risk of leishmaniasis is greatest in regions where sandflies and Leishmania parasites are present. Environmental conditions that support sandfly populations, including warm temperatures and humid climates, can increase the likelihood of exposure.
Risk factors for leishmaniasis in horses include: [9][13][14][15]
- Living in endemic regions
- Outdoor housing during periods of peak sandfly activity
- Exposure to wooded, brushy, or rural environments
- Travel to areas where leishmaniasis is common
- Environmental conditions that support sandfly breeding
Not all horses exposed to Leishmania parasites develop clinical disease. Factors such as parasite species, parasite load, and the horse’s immune response may influence whether infection causes noticeable clinical signs.
Table 2. Risk factors for leishmaniasis in horses and practical prevention steps
| Risk factor | How it increases sandfly exposure | Practical prevention steps |
|---|---|---|
| Living in an endemic region |
|
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| Outdoor housing during peak insect activity |
|
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| Wooded, brushy, or rural environments |
|
|
| Travel to areas where leishmaniasis is common |
|
|
| Warm, humid conditions |
|
|
Diagnosing Leishmaniasis in Horses
Because the skin lesions associated with leishmaniasis can resemble several other equine skin conditions, laboratory testing is required to confirm a diagnosis.
Veterinarians typically begin with a physical examination and review of the horse’s medical history, including any travel to regions where leishmaniasis is known to occur. In addition to evaluating suspicious skin lesions, veterinarians may consider the horse’s geographic location and travel history.
A skin biopsy is often needed to diagnose leishmaniasis in horses. Tissue samples can be examined under a microscope for inflammatory changes and evidence of Leishmania parasites. Polymerase chain reaction (PCR) testing may also be used to detect parasite DNA and help confirm infection. [2][3][16][17]
Several conditions can produce lesions similar to those seen in horses with leishmaniasis. As a result, veterinarians must rule out other skin diseases before confirming the diagnosis. Conditions that may resemble leishmaniasis in horses include: [1]
- Sarcoids
- Squamous cell carcinoma
- Habronemiasis
- Pythiosis
- Eosinophilic granulomas
- Fungal skin infections
- Bacterial granulomas
Accurate diagnosis is important because treatment recommendations and prognosis can vary depending on the underlying cause of the lesion.
Treating Leishmaniasis in Horses
Veterinary treatment for leishmaniasis in horses is aimed at eliminating skin lesions and preventing recurrence. The treatment approach depends on the size, location, and extent of the lesions, as well as the horse’s overall health.
Surgical Removal
Surgical excision is the most commonly reported treatment for equine leishmaniasis. Because many affected horses develop a single localized lesion, complete removal of the affected tissue may be sufficient to resolve the infection. [2]
The likelihood of success depends on factors such as lesion size, location, and whether the affected tissue can be completely removed. Many cases report surgical treatment resulting in favorable outcomes. [2]
Horses undergoing surgery may require routine wound care and follow-up examinations to monitor healing.
Medical Management
Medical therapy may be considered when lesions are extensive, occur in multiple locations, or cannot be easily removed through surgery.
Various antiprotozoal medications have been used to treat leishmaniasis in other species, and some have been reported in equine cases. However, limited research is available on the effectiveness of these treatments in horses. [18][19]
Because equine leishmaniasis is uncommon, treatment recommendations are often based on individual case reports rather than large clinical studies. Veterinarians may tailor treatment plans according to the horse’s clinical signs, lesion characteristics, and response to therapy.
Follow-Up Care
Regular veterinary follow-up is important after treatment. Re-examination allows veterinarians to assess healing, monitor for the development of new lesions, and determine whether additional treatment is necessary.
Horse owners should continue monitoring affected areas after treatment and report any changes in appearance or signs of recurrence to their veterinarian. Ongoing follow-up helps ensure persistent or recurring lesions are addressed promptly.
Prognosis for Horses with Leishmaniasis
The prognosis for horses with leishmaniasis is generally favorable, particularly when disease is limited to localized skin lesions. Many affected horses respond well to treatment, and recurrence appears to be uncommon following successful management.
Horses with a small number of localized lesions generally have a better prognosis than those with extensive or difficult-to-treat lesions. The location of the lesion, the amount of tissue affected, and the horse’s response to treatment may also influence the outcome.
Some reports have documented spontaneous regression of lesions in affected horses. However, veterinary evaluation is still recommended to confirm the diagnosis and rule out other conditions that may require treatment. [9][16]
Because systemic disease is uncommon in horses, most affected animals are expected to recover with appropriate veterinary care. Early diagnosis and treatment can help improve outcomes and reduce the risk of complications.
Preventing Leishmaniasis in Horses
Because leishmaniasis is transmitted by sandflies, prevention focuses on reducing exposure to these insect vectors. While complete prevention may not be possible in endemic regions, management practices that limit contact with sandflies can help reduce the risk of infection.
Vector Control
Vector control is the most important prevention strategy for leishmaniasis because the disease is transmitted by infected sandflies. Reducing the number of bites a horse receives can help lower the chance of exposure, especially in regions where Leishmania parasites are endemic.
Sandflies are small biting insects that can be difficult to exclude completely from barns and shelters. They may be active during low-light periods, including dusk, dawn, and overnight, depending on the region and season. Horses kept outdoors during these periods may have greater exposure to bites.
Practical control measures include using veterinarian-approved insect repellents, fly sheets, fly masks, and other physical barriers when appropriate. Horses in high-risk areas may also benefit from being stabled during peak sandfly activity, particularly if barns are well ventilated and fitted with fine-mesh screens where feasible. [13][20]
Environmental Management
Environmental management strategies can help limit sandfly populations around horse facilities. Reducing dense vegetation and organic material near barns and paddocks may decrease suitable habitats for sandflies and other biting insects. [21][22]
Maintaining clean barn areas and implementing insect control measures can further reduce opportunities for vector exposure.
Travel Considerations
Horse owners traveling to regions where leishmaniasis is endemic should be aware of the potential risk of infection. Monitoring horses for unusual skin lesions following travel may support earlier diagnosis and treatment if disease develops.
Because no vaccine is currently available for the prevention of equine leishmaniasis, vector control and environmental management remain the primary strategies for reducing disease risk.
Frequently Asked Questions
Here are some frequently asked questions about leishmaniasis in horses:
Leishmaniasis in horses is a parasitic, vector-borne disease caused by Leishmania protozoa and transmitted primarily through the bites of infected sandflies. Although leishmaniasis is more common in humans and dogs, horses can become infected in regions where the parasite and sandfly vectors are present. Most equine cases affect the skin, causing firm nodules, ulcers, crusting, scaling, swelling, or hair loss. Systemic illness is uncommon in horses, and most reported cases are localized to the skin. [1][2][3]
Signs of leishmaniasis in horses most often involve localized skin lesions. Affected horses may develop one or more firm nodules, ulcerated lesions, crusting, scaling, hair loss, swelling, or skin inflammation. Lesions are commonly reported on the head, ears, neck, limbs, or genital region. Rarely, horses with severe parasite burdens may show systemic signs such as lethargy, exercise intolerance, decreased appetite, or dullness. [1][3][10]
Leishmaniasis is rare in horses. When infections lead to clinical signs, lesions in horses most often appear on the head, ears, neck, limbs, or genital region. These lesions may start as firm skin nodules and later become ulcerated, crusted, scaly, swollen, or hairless. Some horses have a single localized lesion, while others may develop multiple cutaneous lesions. Because the appearance can overlap with other skin diseases, location alone is not enough to confirm the diagnosis. [3][10]
Horses get leishmaniasis when they are bitten by an infected female sandfly carrying Leishmania parasites. Sandflies acquire the parasites while feeding on infected animals and can transmit them during later blood meals. Once inside the horse's skin, the parasites invade immune cells called macrophages, where they can survive and multiply. This can trigger inflammation and lead to nodules, ulcers, and other skin lesions. [3][4][5][11][12]
Leishmaniasis is not contagious between horses through direct contact. Horses do not typically infect each other by touching, sharing space, or contacting skin lesions. Infection occurs when an infected sandfly bites a horse and transmits the parasite. This means prevention focuses on reducing sandfly exposure rather than isolating affected horses from direct contact.
Humans typically get leishmaniasis from the bite of an infected sandfly, not from direct contact with horses. Horses are considered incidental hosts and are not regarded as major reservoir species maintaining the parasite in endemic regions. However, a case of leishmaniasis in a horse may indicate that infected sandflies are present in the local environment. People and animals in endemic regions should use appropriate measures to reduce sandfly bites.
Leishmaniasis in horses has been reported in Europe, North and South America, Africa, and Asia. Cases are most likely in regions where environmental conditions support sandfly populations and Leishmania parasites are present. Warm temperatures, humid climates, wooded or brushy areas, and rural environments may increase exposure risk. Horses that travel to endemic areas may also be at higher risk of infection. [8][9][13][14][15]
Horses are most at risk of leishmaniasis when they live in or travel to regions where infected sandflies are present. Outdoor housing during peak sandfly activity, exposure to wooded or brushy environments, and warm, humid conditions can increase the chance of bites. Not every exposed horse develops clinical disease. Parasite species, parasite load, and the horse's immune response may influence whether visible signs appear. [9][13][14][15]
Horses can get leishmaniasis after traveling if they are exposed to infected sandflies in an endemic region. Skin lesions may develop after exposure, especially when horses spend time outdoors during periods of sandfly activity. Owners should monitor horses for unusual nodules, ulcers, crusting, swelling, or hair loss after travel to areas where leishmaniasis occurs. Suspicious lesions should be examined by a veterinarian, particularly if they grow, ulcerate, or fail to heal.
Leishmaniasis in horses is usually not a systemic disease, but it can still require veterinary care. Most reported cases are limited to the skin and have a generally favorable prognosis when lesions are diagnosed and managed appropriately. The main concern is that lesions can worsen, recur, or resemble more serious conditions such as sarcoids or squamous cell carcinoma. Veterinary testing is important so the correct condition is identified and treated.
Leishmaniasis in horses is diagnosed through veterinary examination and laboratory testing. A veterinarian may assess the horse's skin lesions, medical history, geographic location, and travel history. Skin biopsy is often used to examine tissue for inflammatory changes and evidence of Leishmania parasites. Polymerase chain reaction testing may also be used to detect Leishmania DNA and help confirm infection. [2][3][16][17]
Skin conditions that can be mistaken for leishmaniasis in horses include sarcoids, squamous cell carcinoma, habronemiasis, pythiosis, eosinophilic granulomas, fungal skin infections, and bacterial granulomas. These conditions can also cause nodules, ulcers, crusting, or abnormal skin growths. Because treatment and prognosis differ depending on the underlying cause, laboratory testing is important. A veterinarian can determine which diagnostic tests are most appropriate for the horse's lesions. [1]
Leishmaniasis in horses is treated based on the size, location, number, and extent of the lesions. Surgical excision is the most commonly reported treatment, especially when a horse has a single localized skin lesion that can be completely removed. Medical therapy may be considered when lesions are extensive, occur in multiple locations, or cannot be easily removed surgically. Because equine leishmaniasis is uncommon, treatment plans are usually tailored to the individual horse. [2][18][19]
Horses can often recover from leishmaniasis with appropriate veterinary care, especially when the disease is limited to localized skin lesions. The prognosis is generally favorable when lesions are identified early and can be treated effectively. Horses with small, localized lesions usually have a better outlook than horses with extensive or difficult-to-treat lesions. Follow-up examinations help monitor healing and check for new or recurring lesions.
Leishmaniasis lesions in horses have occasionally been reported to regress spontaneously, but veterinary evaluation is still recommended. Skin nodules and ulcers can resemble other diseases, including conditions that may require prompt treatment. A veterinarian can confirm whether the lesion is caused by Leishmania parasites or another skin disorder. Even when a lesion appears to improve, monitoring is important to detect recurrence or new lesions. [9][16]
You should call a veterinarian for suspected leishmaniasis if your horse develops unexplained skin nodules, ulcers, crusting, scaling, hair loss, or localized swelling. Prompt veterinary attention is especially important if lesions grow, become ulcerated or painful, appear in multiple locations, or fail to respond to routine care. Horses living in or returning from endemic regions should be evaluated if suspicious skin lesions develop. Early diagnosis can help guide treatment before lesions become more extensive.
Leishmaniasis prevention in horses focuses on reducing exposure to infected sandflies. Fly sheets, fly masks, and veterinarian-approved insect repellents may help protect horses from bites. Housing horses indoors during peak sandfly activity, especially around dawn, dusk, or overnight in high-risk areas, may further reduce exposure. Environmental management, such as reducing dense vegetation and organic material near barns and paddocks, can also help limit insect habitats. [13][20][21][22]
Leishmaniasis cannot always be completely prevented in horses living in endemic regions because sandflies can be difficult to exclude entirely. However, reducing the number of bites a horse receives can lower the chance of exposure. A layered approach that combines insect repellents, physical barriers, stabling during high-risk periods, and environmental management is the most practical strategy. Owners in endemic regions should also monitor horses regularly for new or unusual skin lesions.
There is currently no vaccine available to prevent leishmaniasis in horses. Prevention relies on vector control, insect avoidance, and environmental management. These measures are especially important in regions where Leishmania parasites and sandfly vectors are known to occur. Horse owners should also monitor for unusual skin lesions after travel to endemic areas.
Summary
Leishmaniasis is a vector-borne disease caused by Leishmania parasites and transmitted through the bites of infected sandflies.
- Although uncommon in horses, the disease has been reported in regions of Europe, North and South America, Africa, and Asia
- Most horses develop localized skin lesions, including nodules, ulcers, crusting, and hair loss
- Diagnosis typically requires a veterinary examination, skin biopsy, and laboratory testing to distinguish leishmaniasis from other skin conditions
- Surgical removal of localized lesions is the most commonly reported treatment, though medical therapy may be considered in some cases
- The prognosis is generally favorable, particularly when lesions are identified and treated early
- Preventing leishmaniasis focuses on reducing exposure to sandflies through insect control and environmental management practices
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