Your Healthy Horse


Learn why your horse needs a Cog­gins test.

A neg­a­tive Cog­gins test for equine in­fec­tious ane­mia is im­por­tant — and some­times re­quired. Here’s what you need to know. BY ELEANOR M. KELLON, VMD

WWhat if you knew of an equine dis­ease that had no cure, no treat­ment, and in many cases would re­quire you to destroy your horse if he be­came in­fected? You’d prob­a­bly find that pretty scary. Well, such a dis­ease does ex­ist, but luck­ily it’s rare enough that we tend to for­get about it. Be­cause the Cog­gins test has proved so ef­fec­tive, equine in­fec­tious ane­mia (EIA) re­ceives very lit­tle at­ten­tion these days. But it’s still around, and it’s still a killer.

Here, I’ll first go over the causes of EIA and ex­plain how the virus spreads. Then I’ll tell you why get­ting a Cog­gins test for your horse is so im­por­tant, es­pe­cially if he’s on the road.

How EIA Spreads

Also known as “swamp fever,” EIA is caused by in­fec­tion from a lentivirus, the same fam­ily of virus that causes ac­quired im­mune de­fi­ciency syn­drome (AIDS) in peo­ple. How­ever, peo­ple can’t get AIDS from the equine virus, nor can horses get EIA from the hu­man virus.

EIA can’t be spread by ca­sual con­tact. It’s usu­ally trans­mit­ted via large bit­ing flies, which carry virus-packed blood from an in­fected horse to a neigh­bor­ing horse.

Although trans­mis­sion through sex­ual con­tact has never been doc­u­mented, the virus has been known to show up in se­men. Pas­sage of virus in saliva and ma­nure is also a pos­si­bil­ity.

Peo­ple can spread the in­fec­tion by us­ing the same nee­dle or den­tal in­stru­ments with blood on them on dif­fer­ent horses.

Move­ment of in­fected horses to new ar­eas is how EIA can travel long dis­tances, as the bit­ing flies don’t travel far. As yet, there’s no ef­fec­tive vac­cine or treat­ment for this po­ten­tially fa­tal dis­ease.

EIA Symp­toms

An in­fected horse may be symp­tom-free for a long time, un­til some stress (such as an­other in­fec­tion, ship­ping, hard ex­er­cise, etc.) weak­ens his im­mune sys­tem and the virus be­comes ac­ti­vated. Other horses may never show they have the in­fec­tion and are called in­ap­par­ent car­ri­ers.

EIA hides in­side a type of white blood cell (the macrophage) that car­ries it through­out the horse’s body. High­est con­cen­tra­tions are usu­ally in the lymph nodes and lym­phatic sys­tem, liver, spleen, kid­ney, and bone mar­row, but it can go to any or­gan, even caus­ing en­cephali­tis in the brain.

The symp­toms of EIA in­fec­tion are only ev­i­dent when the virus is ac­tive. Fever is the first sign, but it’s eas­ily missed. The next symp­tom is usu­ally ane­mia, which oc-

curs be­cause chem­i­cal-sig­nal­ing mol­e­cules be­come at­tached to the red cells and trig­ger the im­mune cells to en­gulf the cells. This causes weak­ness, de­pres­sion, poor oxy­gen de­liv­ery, and pos­si­ble or­gan dam­age.

As the dis­ease pro­gresses, prob­lems with clot­ting ap­pear be­cause the platelets are de­stroyed. The white cell num­bers also start to de­cline. Even­tu­ally, the liver and other or­gans be­come da­m­aged. The horse slowly but steadily loses weight, show­ing swelling (edema) of the belly and legs.

If EIA isn’t sus­pected, the horse will prob­a­bly be treated with de­worm­ings, di­etary changes, and an­tibi­otics, but none of these things help. Once horses be­come symp­to­matic, they show a slow but steady wast­ing away un­til the dis­ease it­self kills them or they’re eu­th­a­nized.

The Cog­gins Test

The first step in diagnosis is the Cog­gins test, a blood test that de­tects an­ti­bod­ies to the EIA virus. When this is pos­i­tive, two more spe­cial­ized and more sen­si­tive tests are done to make sure the diagnosis is cor­rect.

Since Leroy Cog­gins, DVM, de­vel­oped the test in 1970, cases of EIA have dropped dra­mat­i­cally. Gov­ern­men­tal agen­cies have taken dras­tic mea­sures with pos­i­tive horses, gen­er­ally re­quir­ing euthana­sia, though quar­an­tine is some­times al­lowed.

Ev­ery state has laws re­gard­ing manda­tory Cog­gins test­ing. While the laws vary a bit from state to state, they’ll usu­ally re­quire test­ing of horses be­ing shipped and com­pet­ing in shows or races, as well as horses be­ing sold at pub­lic auc­tion.

Any horse that tests pos­i­tive will have to ei­ther be de­stroyed or kept quar­an­tined for the rest of his life.

The se­ri­ous na­ture of the in­fec­tion, the con­stant threat that horses with ac­tive in­fec­tion pose to other horses, and the in­abil­ity to treat the in­fec­tion are why it’s con­sid­ered so im­por­tant to try to iden­tify in­fected horses and re­move them from con­tact with healthy ones. TTR

CLIXPHOTO.COM It’s im­por­tant to get a Cog­gins test for your trav­el­ing horse, as move­ment of in­fected horses to new ar­eas is how EIA can travel long dis­tances.

Although it has be­come rel­a­tively rare, EIA is an in­sect-borne dis­ease, so it’s hard to pro­tect horses that are con­stant tar­gets of bit­ing flies.

BOB LAN­GR­ISH PHOTO As yet, there’s no ef­fec­tive vac­cine or treat­ment for this po­ten­tially fa­tal dis­ease. A sim­ple blood test, called a Cog­gins test, can deter­mine if a horse is a car­rier of equine in­fec­tious ane­mia.

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