Fatal equine meningoencephalitis in the United Kingdom caused by the panagrolaimid nematode Halicephalobus gingivalis: case report and review of the literature.
Authors: Hermosilla C, Coumbe K M, Habershon-Butcher J, Schöniger S
Journal: Equine veterinary journal
Summary
# Editorial Summary A 10-year-old Welsh gelding presented with progressive neurological signs—initial behavioural changes escalating to severe ataxia, altered mental status and cranial nerve deficits—which led to euthanasia when symptomatic treatment failed to arrest decline. Post-mortem examination identified extensive eosinophilic and granulomatous meningoencephalitis predominantly affecting the cerebellum and brainstem, with intralesional adult nematodes, larvae and eggs consistent with *Halicephalobus gingivalis*, a facultative neurotropic free-living panagrolaimid nematode. Whilst infection by this organism is exceptionally uncommon, this UK case highlights the importance of including halicephalobosis in the differential diagnosis for equine central nervous system disease, particularly where other parasitic causes are being considered; notably, the extensive localisation within neural tissue in this case was atypical, as the parasite ordinarily disseminates haematogenously to multiple organs. Given the taxonomic revision of *H. gingivalis* (previously classified as *Micronema deletrix* or *Halicephalobus deletrix*), practitioners should be aware of current nomenclature when reviewing literature on free-living nematode infections in horses, though the rarity of this condition means clinical recognition remains challenging and post-mortem diagnosis may be the only confirmatory route.
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Practical Takeaways
- •Include free-living nematode infection (H. gingivalis) in the differential diagnosis when horses present with progressive CNS signs that do not respond to standard treatment, though this remains an extremely rare cause
- •Be aware that this parasite's taxonomy has changed; older literature may refer to it as Micronema deletrix or Halicephalobus deletrix, which may affect literature searches
- •Recognize that despite the rarity of this condition, CNS helminthic infections in horses warrant comprehensive post-mortem examination and histopathology to establish definitive diagnosis
Key Findings
- •Fatal eosinophilic and granulomatous meningoencephalitis in a 10-year-old Welsh gelding caused by Halicephalobus gingivalis, a free-living panagrolaimid nematode
- •Lesions were locally extensive, primarily affecting the cerebellum and brain stem, with intralesional adult nematodes, larvae and eggs
- •Clinical presentation progressed from behavioural abnormalities to severe ataxia and reduced mentation, with no response to symptomatic treatment
- •H. gingivalis should be included in differential diagnosis for equine CNS disease, though infection remains extremely rare