Fatal equine meningoencephalitis in the United Kingdom caused by the panagrolaimid nematodeHalicephalobus gingivalis: Case report and review of the literature

Abstract

A fatal case of eosinophilic and granulomatous meningoencephalitis caused by the free-living panagrolaimid nematode Halicephalobus gingivalis is reported in a 10-year-old Welsh gelding in the United Kingdom. Clinical examination first revealed behavioural abnormalities which rapidly progressed to severe ataxia, reduced mentation status and cranial nerve signs. Despite symptomatic treatment no amelioration of neurological signs was achieved and the horse was subjected to euthanasia. A complete post mortem examination revealed eosinophilic and granulomatous meningoencephalitis mainly affecting the cerebellum and brain stem with intralesional adult nematodes, larvae and eggs. There was also eosinophilic meningitis of the cervical spinal cord. The intralesional nematodes were morphologically consistent with the panagrolaimid nematode H. gingivalis. Although infection by this facultative neurotropic parasite is extremely rare, it needs to be considered in the differential diagnosis of central nervous signs in horses and, in particular, other equine helminthic infection of the central nervous system. This fatal case is unusual since lesions were locally very extensive and the nematodes did not colonise haematogenously to other organs as seen often in equine halicephalobosis. As the taxonomy of H. gingivalis has changed and some recent reports in the literature still refer to this species as Micronema deletrix or Halicephalobus deletrix, we here provide a short update of the species and some insights on the order Tylenchida, which contains free-living nematodes with parasitic tendencies.

Halicephalobus gingivalis: A Rare Cause of Fatal Meningoencephalomyelitis in Humans

“…Treatment of H. gingivalis infections in other animals is mostly unsuccessful and may be caused by the inability of anthelmintic drugs to cross the blood-brain barrier and penetrate the granulomatous lesions in the brain or a lack of sensitivity of H. gingivalis to anthelmintic drugs such as ivermectin and benzimidazole. 4 There have been only two reports of successful treatment of extra-central nervous system-localized halicephalobus infections in horses with ivermectin alone or with diethylcarbamazine. 10,11 An approach similar to treatment of disseminated strongyloidiasis may be prudent, specifically use of ivermectin alone or in combination with albendazole, 12 but this approach would require antemortem clinical suspicion of halicephalobiasis.…”

“…It is capable of infecting and reproducing in vertebrates, including horses, [2][3][4][5] zebras, 6 and humans. [7][8][9] The genus Halicephalobus contains many species, of which only H. gingivalis has been reported to infect vertebrates and is morphologically distinct from the other seven species.…”

Massive mandible osteolysis caused byHalicephalobus gingivalisin a mare

“…Both structures presented a very large number of nematodes that allowed precise identification of the eggs, larvae and adult forms of H gingivalis (Anderson and others 1998, Gardiner and Poynton 1999, Hermosilla and others 2011) (Fig 2). H gingivalis has a cylindrical body, an average of 20 µm in diameter and 370 µm in length.…”

Maxillary osteomyelitis due to Halicephalobus gingivalis and fatal dissemination in a horse

“…It has been hypothesized that the inability of antihelmintics to cross the blood-brain barrier (Plumb 2002), the lack of sensitivity to ivermectin therapy in H. gingivalis, the difficulty of obtaining an appropriate antemortem diagnosis in the absence of visible granulomatous lesions and the rapid evolution of the condition -especially when the nervous system is involved -may contribute to the poor prognosis (Ferguson et al 2008, Hermosilla et al 2011. In this particular case, we speculate that the prognosis for recovery was poor due because the nematode was protected from high concentrations of the drug by bone sequestration (Bröjer et al 2000), as well as the severe and rapid progression of the insult to the kidneys.…”

“…After the nematodes enter a horse, they reproduce via parthenogenesis which causes granulomatous inflammation and destruction of host tissues (Ruggles et al 1983). They can cause meningoencephalitis (Bryant et al 2006), nephritis, gingivitis, osteomyelitis, posthitis, orchitis, papillitis, retinitis (Hermosilla et al 2011), uveitis, (Kinde et al 2000), ocular parasitism (Rames et al 1995), radiculomeningomyelitis (Johnson et al 2005) and arthritis (Simpson et al 1988). The condition is usually fatal and there are only three reports of successful treatment following the administration of ivermectin an antiparasitic drug, although the lesions did not affect the central nervous system (CNS) (Dunn et al 1993, Simon et al 2001, Schmitz and Chaffin 2004, Ferguson et al 2008.…”