EQUUS - - Epm -

since the mouse model hasn’t been the best. Now we are talk­ing about us­ing [in­ter­me­di­ate hosts, such as] rac­coons, cats or ar­madil­los. Our goal is to avoid us­ing horses, if pos­si­ble. We re­al­ize that at some point we may have to go back to the horse---since it is the host we are most con­cerned about---but we want to use as few horses as pos­si­ble to in­fect with the dis­ease.”

Reed adds, “If we can de­velop a good model, we may go back and start over again at look­ing at a vac­cine. The early vac­cine tri­als did not show good suc­cess. That doesn’t mean we should give up on cre­at­ing a vac­cine, but if we could do some­thing like feed a low level of an an­tipro­to­zoal drug and keep the horses from be­com­ing in­fected, it would be very help­ful.”


As with many dis­eases, the ef­fort to com­bat EPM is com­plex and has many fronts. None­the­less two ba­sic ques­tions re­main to be an­swered: Where are horses most likely to en­counter the causal or­gan­isms, and what can be done to pre­vent those who are in­fected from be­com­ing ill?

Work is un­der­way to bet­ter un­der­stand where ex­po­sure to the EPM par­a­sites is great­est. “Un­for­tu­nately there is not a lot of re­cent data on preva­lence,” says Pusterla. “Some states are ‘hot’ states, mean­ing higher in­fec­tion rates in the horse pop­u­la­tion. There are more EPM cases in Ok­la­homa, Ohio, Ken­tucky and Texas, for in­stance, along with some of the South­ern and Mid­west­ern states. By con­trast we see fewer cases in some of the North­ern and West­ern states.

“To look at in­fec­tion rates, we sam­ple 100 healthy horses and see how many of them have ev­i­dence of past in­fec­tion based on an­ti­body titers,” Pusterla adds.

With no vac­cine cur­rently avail­able, your best strat­egy for re­duc­ing your horse’s risk of de­vel­op­ing equine pro­to­zoal myeloen­cephali­tis (EPM) is to take steps to limit his ex­po­sure to the pri­mary pro­to­zoan that causes it: Sar­co­cys­tis neu­rona, which is spread in the fe­ces of the opos­sum. And that means try­ing to limit the opos­sums that live near your barn and pas­tures. Here are some steps you can take:

• Re­duce po­ten­tial shel­ter. Clear brush piles, and seal off ac­cess to crawlspace­s un­der your sheds and other out­build­ings. Keep shed and garage doors closed.

• Cut off food sources. Opos­sums will eat just about any­thing. Clean up spilled feed im­me­di­ately, and keep grain in sealed con­tain­ers. Use sturdy garbage cans with tight-fit­ting lids. Avoid leav­ing cat or dog food out overnight. Pick up fallen fruit from any fruit trees.

• Keep the food and wa­ter clean. Store hay and bed­ding in a se­cure shed, and throw out any­thing you find con­tam­i­nated with drop­pings. Check out­door hay feed­ers and wa­ter troughs fre­quently for signs of small an­i­mals, and clean them as needed.

• Dis­pose of an­i­mal car­casses quickly. Opos­sums in­gest S. neu­rona by scav­eng­ing the bod­ies of other small an­i­mals that car­ryarry it—es­pe­cially rac­coons, cats, skunks ks and ar­madil­los. Pick up road­kill and other dead an­i­mals you find on or near your farm.

Note: Trap­ping or killing opos­sums is not a goodood so­lu­tion. If your farm is a source rce of food and shel­ter for them, more will come. “I have a grad­u­ate stu­dent look­ing at 5,200 serum sam­ples col­lected from healthy horses dur­ing 2013 across the United States. The study rep­re­sents 17 states in all the ge­o­graphic ar­eas, with ap­prox­i­mately 300 an­i­mals per state. Her job is to de­ter­mine sero­preva­lence for both S. neu­rona and N. hugh­esi. This data will give us a bet­ter idea about where the hot spots are, and what the ac­tual in­fec­tion rate might be.”

Armed with that in­for­ma­tion, a per­son who lived in a hot spot might be able to take ad­di­tional pre­cau­tions with higher risk horses, such as younger ones en­ter­ing stress­ful train­ing. “You’d want to mon­i­tor th­ese horses a bit more closely,” says Pusterla.

Like­wise, re­searchers in the com­ing years also hope to an­swer an­other con­found­ing ques­tion about EPM: Why do some horses de­velop the dis­ease when oth­ers ex­posed to the same par­a­site do not?

“In some states 90 per­cent and in many states over 50 per­cent of the horses in a given area will have an­ti­bod­ies, in­di­cat­ing they have been in­fected,” says Reed. “Yet the in­ci­dence of se­vere dis­ease is much lower than that. Is the rea­son for this dif­fer­ence some­thing about the im­mune func­tion? Are the horses who de­velop the dis­ease im­muno­com­pro­mised? There may be some­thing unique about the im­mune func­tion of those

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