EQUUS - - Contents -

• Risk fac­tors for a rare colic • A way to pre­vent EPM? • Ac­cu­racy of dig­i­tal ther­mome­ters

in­ves­ti­gated • New treat­ment for trapped

epiglot­tis prom­ises fewer re­lapses

A med­i­ca­tion used to treat equine pro­to­zoal myeloen­cephali­tis (EPM) also shows prom­ise as a pre­ven­tive for young horses, ac­cord­ing to new re­search from the Uni­ver­sity of Cal­i­for­nia—Davis.

Char­ac­ter­ized by pro­gres­sive mus­cle weak­ness, in­co­or­di­na­tion or other neu­ro­log­i­cal signs, EPM is pri­mar­ily caused by the pro­to­zoan Sar­co­cys­tis neu­rona, which is shed in the fe­ces of the de­fin­i­tive host, the opos­sum, and can then con­tam­i­nate feed and wa­ter. When a horse is ex­posed to S. neu­rona, his body pro­duces an­ti­bod­ies that can be de­tected in the blood---a process called se­ro­con­ver­sion--- but he will not nec­es­sar­ily be­come ill. EPM oc­curs only if S. neu­rona crosses the blood­brain bar­rier and in­fects the cen­tral ner­vous sys­tem. In some ar­eas of the coun­try, 90 per­cent of the equine pop­u­la­tion tests pos­i­tive for S. neu­rona an­ti­bod­ies.

The Davis study in­volved 33 foals kept on a farm with a his­tor­i­cally high ex­po­sure rate to the pro­to­zoan. “We chose to fo­cus on that group

Younger horses are at in­creased risk of EPM, prob­a­bly be­cause of higher ex­po­sure rates

and stress.

be­cause young per­for­mance horses are at higher risk, prob­a­bly due to a com­bi­na­tion of higher sus­cep­ti­bil­ity and ex­po­sure rates and im­muno­sup­pres­sion due to stress,” says Ni­cola Pusterla, DVM, PhD.

The re­searchers di­vided the study foals into two groups. Ev­ery day for 12 months, they gave one group di­clazuril (Pro­tazil, Merck An­i­mal Health), a med­i­ca­tion used to treat ac­tive cases of EPM. The other group of foals were left un­treated to serve as con­trols.

The young­sters in the treat­ment group re­ceived one-half of the stan­dard dose of di­clazuril, ex­plains Pusterla, be­cause the goal was not to treat the ac­tual dis­ease. “The la­bel dose reaches a very high con­cen­tra­tion of med­i­ca­tion in the blood­stream, which is needed to pen­e­trate the cen­tral ner­vous sys­tem (CNS). With a pre­ven­tive dose, we want to con­trol in­fec­tion at the en­trance site [the GI tract] and not in the CNS.” The

re­searchers drew monthly blood sam­ples from the dams and foals un­til the end of the study pe­riod. The blood was tested for an­ti­bod­ies against S. neu­rona by the in­di­rect flu­o­res­cent an­ti­body test (IFAT).

Be­cause all the foals had re­ceived colostrum from their dams, who car­ried an­ti­bod­ies to S. neu­rona, they had pos­i­tive blood titers for the or­gan­ism im­me­di­ately af­ter birth. How­ever, the ma­ter­nal an­ti­bod­ies de­creased steadily as the young­sters reached wean­ing age. There­after, the un­treated group of foals had a monthly in­crease in an­ti­bod­ies to S.

neu­rona and by the end of the study 83 per­cent tested seropos­i­tive to S. neu­rona. In con­trast, only 6 per­cent of the treated foals tested seropos­i­tive to S. neu­rona at the end of the study.

The re­searchers say th­ese find­ings sug­gest that di­clazuril could be used as a pre­ven­tive treat­ment. “The [study] pro­to­col pre­vents in­fec­tion [with S. neu­rona],” says Pusterla. “This was mea­sured in­di­rectly us­ing serol­ogy. We have no data show­ing that the over­all attack rate for EPM---the per­cent­age of horses in­fected with S. neu­rona that de­velop EPM--in young per­for­mance horses re­ceiv­ing a pre­ven­tive dose is lower that in un­treated horses, [but] you need to re­mem­ber that the over­all attack rate for EPM is rel­a­tively low [less than 1 per­cent].”

He stresses that the half­dose pro­to­col would not be ef­fec­tive on ac­tive cases of EPM: “There is no clin­i­cal data show­ing that half the dose has any ef­fi­cacy in horses di­ag­nosed with EPM.”

Ref­er­ence: “Use of daily di­clazuril pel­leted top dress for the pre­ven­tion of Sar­co­cys­tis neu­rona in­fec­tion in foals,” Amer­i­can As­so­ci­a­tion of Equine Prac­ti­tion­ers 60th An­nual Con­ven­tion Pro­ceed­ings, De­cem­ber 2014

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