NEW TYPE OF STRAN­GLES VAC­CINE I N THE WORKS

EQUUS - - Eq Medical - Ref­er­ence: “Strang­vac: A re­com­bi­nant fu­sion pro­tein vac­cine that pro­tects against stran­gles, caused by Strep­to­coc­cus equi,” Vac­cine, March 2018 Ref­er­ence: “Use of in­frared thermograp­hy to de­tect jugu­lar venipunc­ture in the horse,” Jour­nal of Equine Veter

sig­nif­i­cant re­duc­tion in the av­er­age sur­face tem­per­a­tures where in­jec­tions had been given com­pared to the temperatur­e of the non­in­jected ar­eas. The big­gest dif­fer­ence was seen two hours af­ter in­jec­tion, but sig­nif­i­cant temperatur­e changes were de­tectable for as long as 12 hours. The re­searchers say the de­crease in temperatur­e could be caused by re­duced lo­cal cir­cu­la­tion re­lated to swelling or tis­sue de­gen­er­a­tion in the wake of the in­jec­tion.

The re­searchers con­clude that this tech­nol­ogy could po­ten­tially be used as a screen­ing tool to iden­tify horses who had re­ceived jugu­lar in­jec­tions prior to com­pe­ti­tion. With only a few ex­cep­tions, the United States Eques­trian Fed­er­a­tion pro­hibits the ad­min­is­tra­tion of in­jec­tions in the 12 hours prior to the start of com­pe­ti­tion.

The re­searchers note, how­ever, that the less­con­trolled en­vi­ron­ment of show­grounds or com­pe­ti­tion hous­ing would com­pli­cate the use of in­frared thermograp­hy be­cause of out­side in­flu­ences on skin temperatur­e such as sun­light, ex­er­cise, bathing and wind.

A new type of vac­cine to pro­tect horses against stran­gles may be avail­able by the end of the decade.

Caused by Strep­to­coc­cus equi bac­te­ria, stran­gles is char­ac­ter­ized by high fever and en­large­ment of the lymph nodes of the horse’s head and neck. Over the course of the disease, which typ­i­cally lasts sev­eral weeks, the ab­scessed lymph nodes may burst open to drain co­pi­ous amounts of thick yel­low pus from the nos­trils. Horses who are se­verely af­fected may have trou­ble breath­ing, lead­ing to a “stran­gling” noise that gives the con­di­tion its com­mon name.

Although vac­cines against stran­gles are cur­rently avail­able, re­searchers have been ea­ger to de­velop al­ter­na­tives. “Col­leagues of mine have pub­lished ar­ti­cles on [stran­gles] vac­cine ad­verse re­ac­tions and vac­cines caus­ing clin­i­cal disease,” says Carl Robin­son, PhD, of the An­i­mal Health Trust in Suffolk, Eng­land. Cur­rent stran­gles vac­cines also cause a horse to test pos­i­tive for the or­gan­ism af­ter inoc­u­la­tion, which can con­found di­ag­nos­tic ef­forts dur­ing an out­break.

The new vac­cine, called Strang­vac 4, is a pro­tein vac­cine, which trig­gers the horse’s im­mune re­sponse us­ing pro­teins as­so­ci­ated with S. equi rather than the whole or­gan­ism it­self. “We have se­quenced the whole genome of S. equi and iden­ti­fied a num­ber of what we call sur­face or se­creted pro­teins that are likely to in­ter­act di­rectly with the host, per­form­ing var­i­ous func­tions in­clud­ing at­tach­ment, im­mune eva­sion and nu­tri­ent ac­qui­si­tion,” says Robin­son. “We cloned the genes en­cod­ing eight of these for the Strang­vac 4 vac­cine, pro­duced re­com­bi­nant pro­tein and mixed them in the fi­nal vac­cine for­mu­la­tion.” He adds that as far as he knows this is first pro­tein vac­cine de­vel­oped for horses.

A ma­jor ben­e­fit of this type of vac­cine, says Robin­son, is that it con­fers im­mu­nity without in­ter­fer­ing with di­ag­nos­tic tests that may need to be con­ducted in an out­break: “The re­ally big ad­van­tage of Strang­vac 4, apart from the ef­fi­cacy, is that it does not trip the cur­rently avail­able tests for stran­gles. The PCR tests for the disease are based on DNA tar­gets, which Strang­vac 4 does not con­tain, and the ELISA tests look for an­ti­bod­ies to S. equi pro­teins, which the Strang­vac 4 does not con­tain, and so would also not trip those tests. This al­lows you to vac­ci­nate where disease is cir­cu­lat­ing with the knowl­edge you can tell whether the an­i­mal is dis­eased with ac­tive in­fec­tion or vac­ci­nated.”

In three pre­lim­i­nary tri­als of var­i­ous vac­cine for­mu­la­tions, re­searchers im­mu­nized ponies and then ex­posed them to S. equi. In all of the ex­per­i­ments, only three of 16 ponies vac­ci­nated with Strang­vac 4 de­vel­oped a fever, com­pared to all 16 ponies treated with a placebo.

“There are vir­tu­ally no vac­cines avail­able that will give 100 per­cent pro­tec­tion,” says Robin­son. “It’s a com­mon mis­con­cep­tion that this will be the case. [Strang­vac 4] pre­vented all clin­i­cal signs in some ponies, re­duced them

in oth­ers, and was not ef­fec­tive in oth­ers. What we are try­ing to achieve is a point where good vac­cine ef­fi­cacy, good di­ag­nos­tic tests, good out­break man­age­ment, good biose­cu­rity and good hus­bandry all come to­gether to re­duce the im­pact of the disease and re­duce the num­ber and sever­ity of out­breaks.”

Robin­son says that the ex­per­i­men­tal side of Strang­vac 4 de­vel­op­ment is com­plete and once the reg­u­la­tory pro­cesses are fin­ished, the vac­cine may be avail­able com­mer­cially by 2019 or 2020.

IN­FEC­TION: Stran­gles causes en­large­ment and ab­scess­ing of the lymph nodes.

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