Arteritis in Equine Fetuses Aborted Due to Equine Viral Arteritis (1991)

Equine Viral Art eritis (EVA) is typically a n influenza-like di sease ofhors es only .i -'? While thi s viral infection can cause abo rtio n, recent outbreak s of EVA have been primarily as­ sociated with a respiratory condition in adult hors es. 11 In cases of EVA-induced abortion in mares, th e fetus does be­ co me viremi c, but microscopic lesion s are seldom noted in th e fetus or placenta.v- In one study with experimental cases of EVA abortion, a necrotizing myometritis was reported in th e mare and was suggested as the cause of death and ex­ pul sion o f th e fetus .' This report describe s vascular lesion s in two equine fetuses aborted during an outbreak of EVA in a band of thoroughbred hor ses in Oklahoma. Disseminated inflammat ory lesion s were noted in th e livers, adrenal gland s, spleens, kidn eys, brains, a nd lymph nod es of both fetuses and in th e placenta and heart of one fetu s. Th e placenta was the most seve rely affected ti ssue with a seve re va sculitis. EVA virus was isolat ed from tissues o f both fetu ses. In December 1987, an outbreak of influenza -like clinica l signs began on a thoroughbred breeding farm in northeastern Oklaho ma. Th e illnesses were confined to one barn cont ain­ ing II pregnant mares, two barren mares, and one gelding. Clinically, the affected hors es developed fevers of up to 38.9 C and clear to slightl y cloud y ocular and nasal discharges, with some limb and palpebral ede ma . Typically, an affected mare would abort 10 days aft er the onset of clinical signs. In thi s group of I I pregnant mares, four abort ed and one gave birth to a 3-week premature foal that died within a few hours of birth. Two aborted fetuses from mare Nos. I and 2 and the placenta from mare No.2 were submitted to t he Okla homa Animal Disease Diagnostic Laboratory (Stillwater, OK). The fetus es were in the last trimester o fgestation and were aborted fresh. The lungs of both were ede mato us with a clear gelat ­ inous fluid that thi ckened th e int erlobular septa. Samples of bra in, liver, kidne y, lung, spleen, and th yroid from fetus No. I and brain, liver, kidn ey, lung, spleen, heart, lymph nod es, adrenal gland , and placenta from fetu s No. 2 were exami ned histologically. No abnormalit ies were noted in sections of kid ney, or th yroid gland from fetus No. I. Both fetu ses had widespread inflammatory lesion s in sections of brains, livers, and spleens. Fetu s No. 2 was mor e seve rely affected and had add itiona l inflammatory changes in the placenta, adrenal gland , kidn eys, lymph nodes, and heart . In the sections of placent a from th e fetu s No.2, there was a seve re placentitis characterized by a vasc ulitis. Man y of the arteri oles and a few sma ll muscular arteries in th e lab ­ yrinth adjacent to the chorionic surface were disrupted by a mixed cellular infiltrate , chiefly mon onucl ear cells with oc­ casional neutrophils. Within affected vessels, the whol e cir­ cumference or segments of th e endothelial surface were ne­ croti c with infiltrating mononuclear cells and occasional neut roph ils extend ing past the tuni ca intima int o the tuni ca medi a (Fig. I). Th e myofibrilla r patt ern of th e media was disrupted by vacuoles, karyorrhectic debris, fibrin , a nd cel­ lular infiltr ate. The va scular changes started with swollen endo thelial cell nuclei followed by necro sis and centrifugal spread of the inflammation. In the tuni ca media, clear vac­ uolar spaces deve loped in the disrupted tunica media and tun ica intima. Several spaces contained dens e hyalin drop­ lets. A few thin-walled vessels were affected at the base of th e microcotyledonary proj ections. Th ese were characterized by endo thelial cell necrosis and fibrin oid material in th e tu­ nica media. The trophoblastic epithelium was unremarkabl e. Cha nges in the brains, livers, and spleens of both fetu ses were sim ilar, differing ma inly in seve rity. In th e sections of brain s, a few vessels in th e cerebru ms and ant erior midbrain s were cuffed by numerou s mononucl ear cells and lesser num­ bers of lymphocytes (Fig. 2). Rar ely, a neut rophil or eosi n­ ophil was present. Often th e endo thelial cell nucl ei in affected vessel bulged int o th e lum en. In th e livers, the stroma of most portal triad s had a moderate to mar ked mixed cellular infiltrate th at was primarily co m posed of mon onucl ear cells and lymphocytes (Fig. 3). Th e infiltrate was predominately oriented around portal vessels but occas ionally extended int o th e a dj ace nt hepatic paren ch yma. Occ asiona lly , sma ll bran ches of the hepatic art eri oles had endo thelial necrosis and fibrinoid changes in the tuni ca media. The splenic lym­ phoid nodules contained scatte red foci of necrosi s. Within the trabecula e, several spleni c arte rio les had infiltrates of mononuclear and lym phoid cells in an ede matous adventitia. Th e reaction extended into th e out er tuni ca media of some splenic vessels.