Rhinopneumonitis:

Most horses de­velop this com­mon res­pi­ra­tory in­fec­tion at some point in their lives, but you’ll want to take steps to limit the risks of se­ri­ous con­se­quences.

EQUUS - - Equus - By Lau­rie Bon­ner

Most horses de­velop this com­mon res­pi­ra­tory in­fec­tion at some point in their lives, but you’ll want to take steps to limit the risks of se­ri­ous con­se­quences.

Rhinopneumonitis (“rhino”) in horses is roughly equiv­a­lent to the com­mon cold in peo­ple---it is a highly con­ta­gious res­pi­ra­tory in­fec­tion spread by a virus that passes read­ily from horse to horse. An out­break can spread quickly and eas­ily through a herd. Signs range from mild to se­vere and might in­clude fever, lethargy, cough and nasal dis­charge. There is no spe­cific treat­ment, but most horses re­cover com­pletely within a week or two with rest and sup­port­ive care, which might in­clude drugs to lower a high fever as well as an­tibi­otics if sec­ondary in­fec­tions set in.

But un­like the com­mon cold, rhino has a dark side: It is caused by one of two types of equine her­pesviruses, EHV-1 and EHV-4. Some strains of each or­gan­ism can pass be­yond the res­pi­ra­tory sys­tem and af­fect other parts of the body. If the virus in­fects the ep­ithe­lium that lines the uterus, it can trig­ger abor­tion. The flu­ids from a lost pregnancy con­tain a large quan­tity of virus, which can eas­ily be picked up by other mares in a field, po­ten­tially lead­ing to “abor­tion storms” that sweep quickly through a herd.

Some strains of EHV-1 and -4 can also cause equine her­pesvirus myeloen­cephalopa­thy (EHM), an in­flam­ma­tion of the blood ves­sels that sup­ply the brain and spinal cord. Af­fected horses de­velop neu­ro­log­i­cal signs, in­clud­ing al­tered gaits, ataxia, a floppy tail and uri­nary leak­age. With sup­port­ive care, most horses who are able to re­main on their feet are likely to make a full re­cov­ery from EHM. Out­comes are gen­er­ally worse for those who be­come re­cum­bent, although horses may re­cover with in­ten­sive care, which can in­clude the use of sup­port slings.

Most horses are first in­fected with EHV as foals, and se­ri­ous signs of res­pi­ra­tory ill­ness are more likely to de­velop in those younger than 5 years old. EHV, like her­pesviruses in other species, is never com­pletely cleared from the body. In­stead, the virus goes “la­tent” and hides from the im­mune sys­tem.

How­ever, when a horse is stressed, the viruses may re­ac­ti­vate and cause a new res­pi­ra­tory in­fec­tion. Th­ese later in­fec­tions are of­ten less se­vere, and any out­ward signs may eas­ily go un­no­ticed. How­ever, the horse will be shed­ding the virus in his nasal se­cre­tions, and he can spread the ill­ness to oth­ers. This is how the dis­ease some­times ap­pears in herds that are not ex­posed to out­siders.

Older horses, who have al­ready de­vel­oped nat­u­ral im­mu­nity from pre­vi­ous ex­po­sures to EHV, are less likely to de­velop se­ri­ous res­pi­ra­tory ill­ness when they en­counter a new strain of the virus, but they are more likely than younger horses to de­velop EHM.

VAC­CI­NATE “ATRISK” HORSES

The Amer­i­can As­so­ci­a­tion of Equine Prac­ti­tion­ers in­cludes rhinopneumonitis on its list of “risk-based” dis­eases, which means that vac­ci­na­tion is rec­om­mended only for horses who are more likely to be ex­posed to, or suf­fer more se­ri­ous ef­fects from, the virus. Can­di­dates might in­clude brood­mares, other horses who come in con­tact with mares on breed­ing farms, foals, race­horses and oth­ers who travel fre­quently to com­pe­ti­tions, events and shows.

Vac­ci­na­tion will not nec­es­sar­ily pre­vent an ex­posed horse from de­vel­op­ing rhinopneumonitis, but it can re­duce the sever­ity of the dis­ease if it does oc­cur, and it can also limit the amount of the virus the in­fected horse will shed through nasal se­cre­tions, which may limit con­ta­gion.

Sev­eral prod­ucts are avail­able, which in­clude ei­ther in­ac­ti­vated or mod­i­fied live vac­cines, and two are la­beled for the preven­tion of abor­tion. No vac­cines are la­beled to pre­vent EHM, but in the case of an out­break, vet­eri­nar­i­ans may vac­ci­nate nearby horses who are not yet show­ing signs of ill­ness to limit shed­ding of the virus and help con­trol the spread of the ill­ness.

For foals, the rec­om­men­da­tion is to vac­ci­nate at 4 to 6 months of age, with one booster ad­min­is­tered four to

six weeks later, fol­lowed by a sec­ond booster at the age of 10 to 12 months. There­after, boost­ers are sug­gested at six-month in­ter­vals for at-risk horses. Preg­nant mares may be vac­ci­nated dur­ing the fifth, sev­enth and ninth month of pregnancy, both to pre­vent abor­tion and to con­fer im­mu­nity to the foal.

Your vet­eri­nar­ian will help you de­ter­mine whether vac­cines against EHV are ap­pro­pri­ate for your horse.

BA­SIC BIOSE­CU­RITY

EHV spreads read­ily via di­rect nose-to-nose con­tact, from con­tact with in­fected sur­faces, through shared feed and water, and from air­borne droplets ex­haled by an in­fected horse. The virus can also be car­ried on a per­son’s hands and clothes. Re­cent stud­ies show that un­der the right con­di­tions, the virus can sur­vive up to 21 days or more in water, and it can per­sist for hours or days on hard sur­faces. EHV is so com­mon among horses that pre­vent­ing

Later EHV in­fec­tions are of­ten less se­vere, and out­ward signs may go un­no­ticed. How­ever, the horse will be shed­ding the virus in his nasal se­cre­tions, and he can spread the ill­ness to oth­ers.

ex­po­sure to it en­tirely may not be pos­si­ble, but you can take ba­sic steps to limit your horse’s risks and con­trol the spread of an out­break:

• Pre­vent close con­tact with new horses. When at shows or on trails, avoid let­ting your horse greet oth­ers nose to nose. EHV can also travel via air­borne droplets, so a dis­tance of eight to 10 feet is safer.

• Do not share water buck­ets or equip­ment. Keep a sep­a­rate set of groom­ing tools, buck­ets and other equip­ment for each horse in your care, and avoid bor­row­ing or shar­ing th­ese items at horse shows. One handy way to or­ga­nize your tools is to as­sign each horse a color and use mul­ti­col­ored elec­tri­cal tapes to tag his gear.

• Clean your hands af­ter work­ing with each horse. Make it a habit to wash with soap or use a hand san­i­tizer be­fore mov­ing on to the next horse. A few con­ve­niently placed bot­tles of san­i­tizer around the barn can make this habit eas­ier.

• Iso­late new­com­ers. A horse who has been ex­posed to EHV may in­cu­bate the virus for up to two weeks be­fore show­ing signs of ill­ness, and he might be shed­ding the virus dur­ing that time. Keep any new horse sep­a­rate from the res­i­dent herd for at least two weeks. A sep­a­rate turnout area that does not share a fence line with your other horses would be ideal, but if that’s not an op­tion, con­sider us­ing tem­po­rary fenc­ing to cor­don off a sec­tion of your main pas­ture for the new­comer. You’ll need to use a dou­ble line, spaced 8 to 10 feet apart, to pre­vent nose-to-nose con­tact. In the barn, place the new horse in an end stall, and po­si­tion fans to di­rect air­flow out a door or win­dow rather than to­ward other horses.

• Check for fevers. If you fre­quently travel with your horse, check his tem­per­a­ture twice daily for three days be­fore each trip and con­tin­u­ing up to five days af­ter­ward. If you de­tect a fever, iso­late the horse from oth­ers and con­tact your vet­eri­nar­ian.

TRANS­MIS­SION CY­CLE Equine her­pesviruses are never com­pletely cleared from the body. In­stead, they go “la­tent” and hide from the im­mune sys­tem. When a horse is stressed, the viruses may re­ac­ti­vate and cause a new res­pi­ra­tory in­fec­tion. LATENTLY IN­FECTED HORSE STRESS VIRUS REACTIVATION LA­TENCY ES­TAB­LISHED IN­FEC­TION OF ADULT HORSE/ FOAL IN­FEC­TION OF OTHER HORSES/ FOALS

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