Case 180316 -3

Three-year-old, Assaf ewe

The ewe was down and unable to rise, and the only animal affected in a herd of approximately 200 individuals.

All joints examined were swollen with synovial edema/hyperplasia. There were thickened ovarian, uterine and renal arteries.

One section of uterus is examined in which the large, muscular myometrial arteries are enlarged, dilated and circumferentially surrounded by, and segmentally transmurally disrupted by, numerous lymphocytes, lymphoblasts, and fewer, scattered, plasma cells. The intimal layer is lifted, detached, and often discontinuous and obscured. Individual myocytes within the tunica media and adventitia are separated by clear space (edema). The myometrium, and the interglandular interstitium is otherwise moderately infiltrated by small numbers of scattered segmented and band neutrophils, as well as lymphocytes and fewer macrophages. The superficial endometrium contains a small number of small lymphocytes at the luminal surface.

In situ hybridization using a probe recognizing nucleic acid of OvHV-2 was positive in lymphoblastic cells surrounding the arteries, and scattered in the interglandular interstitium.

Uterus: Severe, diffuse, chronic lymphocytic and plasmacytic arteritis Uterus: Mild, regionally extensive suppurative metritis

Ovine herpesvirus 2 (OvHV-2) is one of a cluster of gammaherpesviruses that cause malignant catarrhal fever (MCF) in ungulates. Sheep are the adapted host species for OvHV-2, and it is generally assumed that OvHV-2 does not cause disease in sheep. Because the majority of sheep are subclinically infected with OvHV-2, detection of viral DNA or antibodies can confirm infection, but cannot uncover disease association. In this case, and in others from the study referenced2 ISH correlates the distribution of OvHV-2 viral nucleic acid with the vasculitis. The results identify OvHV-2 as the likely agent responsible for a sporadic, MCF-like vascular disease in sheep.

There is ample precedent that gammaherpesvirus infections can cause disease even in well-adapted hosts: In humans the best studied gammaherpesvirus is Epstein Barr virus, which can be innocuous, but is also the causative agent of infectious mononucleosis and more rarely cancer. Another example, in veterinary medicine, is the subset of horses infected with equine herpesvirus-5 that develop pulmonary fibrosis.

References

Case contributor:This case was contributed by Dr. Patricia Pesavento, UC Davis, School of Veterinary Medicine.