Im­mune de­fi­cien­cies ex­plained

EQUUS - - Consultant­s -

Q: Last week I had to put down my 7-year-old Amer­i­can Sad­dle­bred due to an ill­ness called com­mon vari­able im­mun­od­e­fi­ciency (CVID). I had never heard of this dis­ease. In ret­ro­spect, I re­al­ize that all the lit­tle is­sues we had over the last two years were a sign of an im­mune sys­tem that was fail­ing. The care we re­ceived from the Univer­sity of Mis­souri Equine Clinic was won­der­ful, and I al­lowed my horse to be necrop­sied in the hopes that more can be learned about this dis­ease and that maybe one day my horse’s death could help save an­other horse’s life. Please let more EQUUS read­ers know about CVID. The con­clu­sion of this dis­ease is nearly al­ways death, and by the time you re­al­ize you have a ma­jor is­sue on your hands, it is too late. Re­becca Peck Lib­erty, Mis­souri

A: Im­mun­od­e­fi­cien­cies are rare con­di­tions in hu­mans and an­i­mals. They can be dif­fi­cult to di­ag­nose, and vet­eri­nar­i­ans may not con­sider them when ini­tially eval­u­at­ing a horse. We of­ten sus­pect an un­der­ly­ing fail­ure of the im­mune sys­tem when in­fec­tions with fevers oc­cur a few times dur­ing the year, and an­tibi­otics are needed more than once to fight them. When im­mun­od­e­fi­cien­cies are hered­i­tary they may man­i­fest in early age; those that we re­fer to as late-on­set man­i­fest later in life. In other cases, tran­sient im­mun­od­e­fi­ciency is caused by im­muno­sup­pres­sive drugs, mal­nu­tri­tion or cer­tain vi­ral in­fec­tions.

Dif­fer­ent kinds of im­mun­od­e­fi­cien­cies re­flect the im­mune sys­tem’s var­i­ous and over­lap­ping strate­gies for fight­ing diverse types of or­gan­isms, in­clud­ing bac­te­ria, viruses, fungi and par­a­sites. These strate­gies in­volve dif­fer­ent cell types and pro­teins that can pre­vent pathogens from in­vad­ing the

body and repli­cat­ing, pro­mote their re­moval and destruc­tion, and trig­ger in­flam­ma­tion or a state of alert­ness. If one of these strate­gies is not func­tional or ab­sent, cer­tain pathogens find a way to in­fect the body, which means that the dif­fer­ent types of im­mun­od­e­fi­ciency re­sult in dis­tinct sus­cep­ti­bil­ity to par­tic­u­lar pathogens. Nev­er­the­less, re­cur­rent in­fec­tions and fevers are com­mon fea­tures of im­mun­od­e­fi­cien­cies. An­timi­cro­bials may help con­trol them but, when the course of treat­ment is over, the in­fec­tion oc­curs again.

Com­mon vari­able im­mun­od­e­fi­ciency (CVID) in the horse is a late-on­set im­muno­logic dis­or­der of in­ad­e­quate an­ti­body pro­duc­tion. Most horses with this con­di­tion are re­ported to have had a healthy life un­til re­cur­rent bac­te­rial in­fec­tions and fevers start to oc­cur, usu­ally af­ter 10 years of age (horses di­ag­nosed with CVID have been as young as 2 years and as old as 23). The con­di­tion can ap­pear in any breed and both gen­ders can be af­fected. The clin­i­cal signs in­clude re­peated episodes of pneu­mo­nia, si­nusi­tis or di­ar­rhea; in­fec­tion of the ab­dom­i­nal cav­ity and liver; in­flam­ma­tion of the eye; skin ab­scesses; menin­gi­tis or neu­ro­logic dis­or­ders; and sus­cep­ti­bil­ity to gas­troin­testi­nal par­a­sites. Weight loss and/or mus­cle loss are com­mon. In­fec­tions are of­ten caused by com­mon types of bac­te­ria.

Blood test­ing in a horse with CVID shows low an­ti­body lev­els, specif­i­cally the serum con­cen­tra­tions of the an­ti­bod­ies IgG and IgM. Typ­i­cally, the cells that pro­duce an­ti­bod­ies, named B cells are also low be­cause their pro­duc­tion in the bone mar­row is im­paired. In some cases, the B cells de­velop, but they do not func­tion prop­erly. The lymph nodes in horses with CVID also tend to be small and lack B cells.

A di­ag­no­sis of CVID can be made based on a horse’s clin­i­cal his­tory of re­cur­rent bac­te­rial in­fec­tions com­bined with im­muno­logic test­ing of blood sam­ples. Some cases may be con­firmed by ex­am­in­ing the lymph nodes dur­ing a necropsy and rul­ing out other dis­eases, such as lym­phoma. There is no ge­netic test avail­able since no ge­netic mu­ta­tions re­lat­ing to CVID have been iden­ti­fied.

To date, CVID is a fa­tal dis­ease in horses. Some cases may be man­aged for a few years with an­tibi­otic ther­apy, but even­tu­ally the re­cur­rent bac­te­rial in­fec­tions will be­come over­whelm­ing. An­ti­body re­place­ment ther­apy has been suc­cess­ful in treat­ing hu­man pa­tients with CVID but is not cost-ef­fec­tive in horses. Bone mar­row trans­plan­ta­tion was at­tempted in one horse but proved to be dif­fi­cult. Stud­ies are cur­rently un­der­way to ex­plore the use of stem cells to re­store B cell pro­duc­tion in the bone mar­row of af­fected horses.

Please ac­cept our con­do­lences for the loss of your horse. We share your hope that what we’ve learned will help us to one day be able to cure this dread­ful dis­ease.

M. Ju­lia B. Felippe, MedVet, MS,

PhD, DACVIM Cor­nell Univer­sity Col­lege of

Vet­eri­nary Medicine Ithaca, New York.

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