Micronema deletrix in the central nervous system of a horse.

This research focused on the fatal case of a 17-year-old Tennessee Walking Horse infected with a parasite called Micronema deletrix. Initial symptoms were laminitis affecting both forefeet, which progressed to severe neurologic signs after 15 days, leading to the horse’s death. Autopsy and microscopic examination revealed parasitic infestation in the leptomeninges (the two innermost layers of the protective tissue surrounding the brain and spinal cord) and resultant pathological changes in the brain and spinal cord.

Case Description and Clinical Presentation

• The study revolves around a 17-year-old male Tennessee Walking Horse suffering from laminitis, an inflammation of sensitive layers inside the hooves. This condition was presented for two months duration and affected both his forefeet.
• Initial treatment included corrective shoeing, a common treatment for laminitis. However, the horse started to show neurological symptoms 15 days after the treatment began, which included unusual stiffness of the forelimbs, increased sensitivity to stimuli, involuntary muscle spasms and abnormal postures, severe lack of coordination, and types of involuntary eye movements (nystagmus).
• The rapid progression of neurological symptoms led to the horse’s death just two days after their onset.

Autopsy and Microscopic Analysis

• Post-mortem examination revealed unusual findings in the horse’s leptomeninges, with certain parts appearing thicker and opaque. Specifically, abnormalities were noted over the brain’s cerebral hemispheres and around the adjacent spinal cord.
• The horse also had a sub-arachnoid hemorrhage, a type of stroke caused by bleeding on the surface of the brain, located at the level of the first and second cervical vertebrae of the spinal cord. However, thoracic and lumbar segments of the spinal cord were not examined in this study.
• The remaining organs and tissues did not present significant abnormalities or lesions.
• Upon microscopic examination, it was discovered that the leptomeninges of both the brain and cervical spinal cord contained extensive infiltration of various immune cells indicating an immune response. These areas contained many pieces of parasites, identified as nematodes.
• Tissue samples from the cerebral hemispheres, cerebellum, brainstem, and cervical spinal cord revealed multiple areas of damage or softening (malacia), primarily located near pathological changes observed in the meninges.

Discussion and Conclusion

• This research presents a case of a horse suffering from a severe and fatal Micronema deletrix infestation, a type of parasite that infected the leptomeninges of the horse’s central nervous system.
• The researchers suggest that the neurological symptoms and subsequent death of the horse might be a result of the parasitic infection causing extensive changes in the brain and spinal cord.