EQUUS - - Eq Medical Front -

New re­search sug­gests that equine her­pesvirus type 1 (EHV-1) can per­sist much longer in wa­ter than pre­vi­ously thought, mean­ing that biose­cu­rity mea­sures taken dur­ing an out­break must in­clude buck­ets, troughs and nat­u­ral wa­ter sources.

EHV-1 is one of five strains of her­pesvirus known to af­fect horses. EHV-1 in­fec­tion typ­i­cally re­sults in res­pi­ra­tory dis­ease (rhinop­neu­moni­tis), but it can also cause preg­nant mares to abort their foals.

In rare cases, the virus at­tacks the cen­tral ner­vous sys­tem, pro­duc­ing signs rang­ing from in­co­or­di­na­tion to paral­y­sis. This po­ten­tially fa­tal neu­ro­log­i­cal form, tech­ni­cally known as equine her­pesvirus myeloen­cephali­tis, is often re­ferred to as “neuro” EHV-1.

Re­searchers at the Leib­niz In­sti­tute for Zoo and Wildlife Re­search and Freie Univer­sität Ber­lin de­cided to in­ves­ti­gate the vi­a­bil­ity of EHV-1 in wa­ter after ob­serv­ing in­ter­species EHV out­breaks at zoos. The an­i­mals were in sep­a­rate en­clo­sures and had no phys­i­cal con­tact.

“Wa­ter wasn’t gen­er­ally con­sid­ered an ‘en­vi­ron­men­tal vec­tor’ for equine her­pesviruses,” ex­plains Anisha Da­yaram, PhD. “It was gen­er­ally as­sumed the virus was not sta­ble in wa­ter. How­ever, many other viruses are known to be passed via wa­ter, although those viruses that have been in­ves­ti­gated to date usually have a di­rect im­pact on hu­mans, such as in­fluenza and noroviruses.”

In a lab­o­ra­tory set­ting, the re­searchers added a known quantity of the virus to a va­ri­ety of wa­ter sam­ples with dif­fer­ent pH lev­els, sed­i­ment con­tent and salt lev­els. In­di­vid­ual sam­ples were also kept at dif­fer­ent tem­per­a­tures: 39, 68 or 86 de­grees Fahren­heit. As days passed, the re­searchers mea­sured the so-called cy­to­pathic ef­fect in each wa­ter sam­ple, which in­di­cates whether an or­gan­ism is able to in­vade cells.

“Cy­to­pathic ef­fect is a term used in cell culture to de­scribe the in­fec­tion of cells by virus par­ti­cles,” says Da­yaram. “This can be vi­su­al­ized un­der a mi­cro­scope, as the healthy cells will usually form a mono­layer; how­ever, when in­fected with virus, the cells be­gin to die, cre­at­ing patches in the mono­layer known as cy­to­pathic ef­fect.”

That data showed that EHV-1 re­mained in­fec­tious for the en­tire length of the study pe­riod---21 days---in al­ka­line wa­ter with a pH of 10, at all tem­per­a­tures and in slightly salty (brack­ish) wa­ter. In wa­ter with lowsed­i­ment con­cen­tra­tions (7.5 to 14 g/L) and high salin­ity (sim­i­lar to sea­wa­ter), the virus was vi­able for 14 days. EHV was in­fec­tious for three days in wa­ter with high sed­i­ment con­cen­tra­tions (50 to 100 g/L) and at low salin­ity lev­els (sim­i­lar to fresh wa­ter). EHV-1 re­mained in­fec­tious for only one day in wa­ter at a pH of 4, which is slightly acidic.

Although this study was limited to a lab­o­ra­tory set­ting, the potential vi­a­bil­ity of EHV-1 in wa­ter sources has im­pli­ca­tions for how to man­age out­breaks in sta­bles.

“This study sug­gests that EHV-1 may be trans­mit­ted via an in­di­rect route such as wa­ter,” says Da­yaram. “So com­mu­nal buck­ets, troughs and any other stand­ing wa­ter sources are potential in­di­rect vec­tors of the virus. If horse own­ers sus­pect an out­break the best thing they can do to limit trans­mis­sion is to iso­late the sus­pected in­di­vid­ual from other horses, make sure they do not share the same wa­ter sources and get the horse tested for EHV to con­firm the in­fec­tion.”

Ref­er­ence: “Long term sta­bil­ity and in­fec­tiv­ity of her­pesviruses in wa­ter,” Sci­en­tific Re­ports, April 2017

Re­search shows that un­der some con­di­tions equine her­pesvirus type 1 can per­sist in wa­ter for up to three weeks.

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