Neurological Changes in Horses Naturally Infected With Halicephalobus gingivalis

This paper aims to describe clinical and neuropathological changes in three horses naturally infected with Halicephalobus gingivalis in Brazil. Three cases of central nervous system (CNS) infection by H. gingivalis were selected, and archival (2003-2014) data (epidemiologic, clinical, and pathologic findings) were reviewed. The pattern, distribution, and severity of microscopic lesions in the CNS were determined. The main clinical signs in all horses included blindness, apathy, ataxia, and incoordination, which could be attributed to telencephalon, basal nuclei, and midbrain damage by migration of H. gingivalis. Thalamus/hypothalamus, hippocampus, and pons also presented significant lesions that could have contributed to proprioceptive dysfunction in all animals. The CNS changes in infected horses included severe multifocal necrotizing granulomatous meningoencephalitis characterized by gray and white matter perivascular infiltration with macrophages, multinucleate giant cells, a few eosinophils and lymphoplasmacytic cuffing within intralesional cross, and longitudinal parasitic sections. Reactive astrocytosis with strong antiglial fibrillary acidic protein immunolabeling surrounding damaged areas in the CNS was also detected. This report highlights the main CNS alterations caused by H. gingivalis infection and may contribute to the diagnosis of this disease in horses.