Neuropathology of naturally occurring Trypanosoma evansi infection of horses.
Authors: Rodrigues A, Fighera R A, Souza T M, Schild A L, Barros C S L
Journal: Veterinary pathology
Summary
# Editorial Summary: Neuropathology of *Trypanosoma evansi* in Horses Naturally occurring *Trypanosoma evansi* infection in horses produces rapidly progressive neurological disease characterised by severe central nervous system pathology, as demonstrated in this neuropathological examination of nine affected cases. Clinical presentation was acute, ranging from 2 to 20 days, with horses exhibiting marked ataxia, blindness, circling behaviour, proprioceptive deficits, and signs of increased intracranial pressure including head pressing and hyperexcitability. Gross examination revealed asymmetric white matter leukoencephalomalacia with yellowish discoloration in seven of nine horses, whilst histological analysis demonstrated necrotising encephalitis affecting all nine cases—predominantly targeting white matter and accompanied by significant oedema, demyelination, and characteristic lymphoplasmacytic perivascular infiltration; spinal cord involvement (meningitis or meningomyelitis) was evident in five of seven horses examined. Immunohistochemical detection of *T. evansi* organisms in perivascular spaces and neuropil confirmed the parasitic aetiology in eight of nine cases. For equine practitioners in endemic regions, this work emphasises the need to include trypanosomiasis in the differential diagnosis of acute, severe neurological disease, particularly ataxia and blindness, as the rapid clinical progression and extensive white matter damage indicate a poor prognosis requiring urgent intervention.
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Practical Takeaways
- •Rapidly progressive neurologic signs (ataxia, blindness, head pressing, circling) over days to weeks in horses should raise suspicion for T. evansi infection in endemic regions; early diagnosis is critical given the short clinical course
- •Post-mortem immunohistochemistry is reliable for confirming T. evansi as the cause of encephalitis when clinical diagnosis is uncertain
- •White matter involvement is a characteristic pathologic feature; imaging may help differentiate this from other causes of equine encephalitis
Key Findings
- •T. evansi causes necrotizing encephalitis in horses with clinical signs including ataxia, blindness, head tilt, circling, and proprioceptive deficits over a 2-20 day clinical course
- •Gross pathology shows asymmetric leukoencephalomalacia with white matter discoloration and gyral flattening in 7 of 9 affected horses
- •Histologic findings reveal white matter-predominant necrotizing encephalitis with edema, demyelination, and perivascular lymphoplasmacytic infiltration
- •T. evansi organisms detected immunohistochemically in perivascular spaces and neuropil in 8 of 9 cases