Halicephalobus gingivalis-associated meningoencephalitis in a Thoroughbred foal.

The article documents a case of a 13-week old racing horse experiencing severe neurological symptoms that had to be euthanized, with an examination later revealing the cause to be an infection by the Halicephalobus gingivalis nematode.

Case Presentation

• The colt, from central Kentucky, presented severe neurological symptoms; including ataxia (lack of muscle coordination), blindness, head tremors, leaning to the right, recumbency (laying down), and seizures.
• Given the acuteness of the onset and the severity of the conditions, the colt was euthanized.

Post-Mortem Examination and Diagnosis

• Post-mortem examination of the colt’s cerebellum revealed a verminous meningoencephalitis. Meningoencephalitis is inflammation of both the brain and the membranes that surround it. The inflammation was identified as both eosinophilic, meaning it related to a specific type of immune response, and granulomatous, which involves formation of granulomas or areas of inflammation often associated with an infection.
• Existence of intact and degenerative small nematodes were discovered within the regions of inflammation. Nemotodes are a type of worm, many species of which can cause disease in animals and humans.

Identification of Halicephalobus gingivalis

• The nematodes were identified as Halicephalobus gingivalis due to their distinct morphological characteristics – dorsoflexed ovaries (bent towards the back) and ventroflexed vulvas (bent towards the belly).
• In addition to morphological identification, intact nematodes that were in a condition compatible with H. gingivalis were recovered from the brain tissues which were reserved for further examination. The recovery was done using tissue maceration and additional laboratory techniques and took place 5 weeks after necropsy.

Conclusion

• This report documents a fatal case of a Thoroughbred colt in Kentucky infected by H. gingivalis, a rare but severe cause of meningoencephalitis in horses. By presenting the case course and diagnosis methods, the report contributes to the pool of knowledge in veterinary diagnosis and treatment of the condition and nematode infections.