DI­AG­NOS­TIC DIF­FI­CUL­TIES

EQUUS - - Eq In Brief -

The most com­mon signs of the dis­ease are weak­ness and in­co­or­di­na­tion (ataxia), pri­mar­ily in the hind limbs. Often, the ef­fects are asym­met­ri­cal--one hind leg will be af­fected more than the other. As the dis­ease pro­gresses, the horse may de­velop mus­cle at­ro­phy. In rarer cases, if the dis­ease af­fects the brain, signs may in­clude fa­cial paral­y­sis, seizures, difficulty swal­low­ing, head tilt and be­hav­ioral changes.

De­ter­min­ing whether a horse has EPM can be dif­fi­cult. Be­cause most who are ex­posed to the pro­to­zoa never de­velop the dis­ease, the pres­ence of an­ti­bod­ies alone is not enough for a di­ag­no­sis. A horse who is positive for an­ti­bod­ies to one of the pro­to­zoa could still have neu­ro­log­i­cal signs due to some other cause.

That said, how­ever, some of the newer test­ing meth­ods---an in­di­rect im­munoflu­o­res­cence an­ti­body test (IFAT) and en­zyme-linked im­munosor­bent as­says (ELISAs)---can be used to de­ter­mine the titer (the con­cen­tra­tion of an­ti­bod­ies) in a blood sam­ple. Although these types of test re­sults are not a de­fin­i­tive di­ag­no­sis, many vet­eri­nar­i­ans con­sider a higher titer, along with neu­ro­log­i­cal im­pair­ment, to be ev­i­dence of prob­a­ble EPM.

The most de­fin­i­tive type of test­ing looks for an­ti­bod­ies to the pro­to­zoa in the cere­brospinal fluid (CSF), which sur­rounds the brain and spinal cord. Ev­i­dence that the or­gan­isms have pen­e­trated the cen­tral ner­vous sys­tem is an even clearer in­di­ca­tion that the horse’s neu­ro­log­i­cal signs are at­trib­ut­able to EPM. Find­ing high titers of an­ti­bod­ies in both the blood and the CSF is the best in­di­ca­tion of EPM that is cur­rently avail­able. How­ever, even this

ev­i­dence is not con­sid­ered de­fin­i­tive proof that the EPM is the cause of any neu­ro­log­i­cal signs. And be­cause ob­tain­ing a sam­ple of CSF is a more tech­ni­cally chal­leng­ing and more in­va­sive pro­ce­dure, many vet­eri­nar­i­ans pro­ceed on the as­sump­tion of EPM based on the blood tests and ob­ser­va­tion of signs alone.

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