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What is Neospora hughesi?

A common disease caused by the Neospora hughesi parasite is equine protozoal myeloencephalitis (EPM). EPM is a common neurological disease found throughout the United States, as well as in Canada, France, and Brazil. It can develop in horses of any age, as all are susceptible to the Neospora hughesi parasite. Symptoms of incoordination, and abnormal gaits and reflexes are signs of a problem with the nervous system, and should be checked by your veterinarian before this condition worsens.

Neosporosis is an infection of the protozoan parasite Neospora hughesi. Once these parasites infect your horse, they can cause thick-walled cysts to form in the spinal cord and central nervous system, muscles of the eyes, brain, or intestines, and can lead to neurological, reproductive, and neonatal diseases.

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Symptoms of Neospora hughesi in Horses

Neurological problems, such as those associated with EPM, can progress gradually or rapidly. Symptoms are variable, depending on which part of the brain is affected, and may stabilize, only to return days to weeks later. Often, your horse will suddenly exhibit more severe signs that result in recumbency. These signs can include:

  • Difficulty swallowing
  • Weight loss
  • Abnormal upper airway function
  • Dullness
  • Anemia
  • Difficulty standing or walking
  • Incoordination
  • Muscle atrophy
  • Weakness in limbs 
  • Loss of body control 
  • Stumbling 
  • Recumbency
  • Abnormal reflexes
  • Head tilt
  • Facial nerve paralysis
  • Difficulty rising
  • Abnormal gait
  • Circling
  • Disorientation 
  • Decreased sensitivity to pain
  • Complete sensory loss
  • Eye abnormalities
  • Blindness
  • Lameness
  • Seizures
  • Abortion
  • Neonatal diseases

Causes of Neospora hughesi in Horses

The cause of a Neospora hughesi infection in horses is the transmission of the parasite into a healthy horse. The complete life cycle of this parasite is currently unknown, which makes the exact path of transmission unclear. It may follow along the path of other similar parasites, wherein ingestion of eggs or sporulated oocysts may lead to an infection. Transmission theories include:

  • Direct contact with oocysts
  • Exposure to contaminated food, water, soil, equipment, or handlers
  • Exposure to opossum scat
  • Transplacental transmission from mother to foal

Diagnosis of Neospora hughesi in Horses

Your veterinarian will begin with a history of symptoms seen in your horse, as well as any history of exposure to possible toxins, viruses, or parasites, such as traveling or exposure to new horses. Any time neurological abnormalities are seen, a complete neurological examination will be performed. This may include imaging techniques, such as X-rays, to help identify any lesions or abnormalities of the brain, spinal cord, or other areas. 

Blood samples are taken for testing, including a CBC, and serum testing that can include indirect immunofluorescence antibody testing. Tests that can narrow down the particular infectious agent infecting your horse can include the Neospora agglutination test (NAT) and an ELISA test that is based on the parasite surface antigen. These tests can help to diagnose EPM and a possible Neospora hughesi infection, but there is not currently a test to differentiate between this parasite and its relative, Neospora caninum. Cerebro-spinal fluid can also be tested.

Muscle biopsies can be performed, which can detect muscle atrophy characteristic of this condition.

Treatment of Neospora hughesi in Horses

Treatment for a Neospora hughesi infection is mainly through the use of anticoccidial drugs, such as ponazuril, diclazuril, or a sulfadiazine/pyrimethamine combination. These drugs work by interfering with the metabolism of folic acid and the conversion of purine and pyrimidine nucleotides, processes which are necessary for the survival of the parasite. There are side effects related to the use of these drugs, which can include bone marrow suppression, hives, diarrhea, weight loss, and neonatal disease if used in pregnant mares.

Other medications that may be prescribed include nonsteroidal anti-inflammatory drugs to prevent neurological symptoms from worsening during treatment, corticosteroids and dimethyl sulfoxide to control inflammation, selenium, and vitamin E as an antioxidant. Treatments can run up to 2 months.

Recovery of Neospora hughesi in Horses

Recovery for your horse is variable, and depends on the severity of the infection and symptoms before treatment. Often, treatment can result in a regression of symptoms, but those symptoms may reappear after treatment ends. Your horse may also continue to deteriorate. Your veterinarian will discuss your horse’s chances of recovery based on his particular condition.

Prevention of this challenging infection can be achieved through regular biosecurity measures, such as:

  • Using routine sanitation and hygiene practices
  • Limiting exposure to new animals
  • Preventing your horse from eating off the ground
  • Ensuring water and feed is clean and uncontaminated
  • Preventing exposure to wildlife
  • Preventing exposure to opossum scat
  • Preventive use of coccidiostatic and coccidiocidal drugs