The clinical signs are apathy, listlessness, drowsiness, circling, difficulty backing, staggering, ataxia, paresis.  Death can occurr after a few days.
In survivors, mental deterioration (dummy horses) is frequent.
Eating contaminated corn can induce the well known
Equine Leukoencephalomalacia
Fumonisin are mycotoxins produced mainly by Fusarium fungi, especially F. verticillioides. A. niger (especially industrial strains) can also produce Fumonisins B2, B4, B6, but probably less B1.
Fusarium proliferate on corn, the key source of fumonisins. A. niger proliferates on coffee, grapes and raisins.
Fumonisin has been found in rice sold in Canada ( Bansal, 2011).
This takes us back to 1983, in the extreme South of the United States, near the Texas border, to Cameron County
Horses (and mules, donkeys...and even carp fish) are liable to eat such polluted feed.
Horse with Equine enkephalomalacia
this horse is
displaying: staggering, ataxia, paresis. drowsiness, listlessness. Death will occurr after a few days.

Experimental demonstration of toxicity for cerebellar Purkinje cells
Cerebellar Purkinje cells play a key role in the control of gait, body equilibrium, adjusting of position. Degeneration of rat Purkinje cells, in culture in vitro with Fumonisine B1, has been demonstrated (Furuya, 1995)
In this area 34% of population is below the level of poverty, and often subsides largely on home-made tortillas, with the corn they can find.
....the corn they can find, that is to say the sort of corn that contaminated the horses......

Please also use this Fumonisin specific drop down menu