Pathological Features of Systemic Necrotizing Vasculitis (Polyarteritis Nodosa) in Sheep

First reported case in an Irish flock of MCF- like systemic necrotizing vasculitis in sheep associated with ovine herpesvirus 2

BACKGROUND

Ovine gammaherpesvirus 2 (OvHV-2) is the causative agent of sheep associated malignant catarrhal fever (MCF). As sheep are the adapted host for OvHV-2, it is generally presumed that infection is not associated with disease in this species. However, a recent case review combined in-situ hybridisation, PCR and histopathology and correlated the viral distribution with systemic necrotizing vasculitis and concluded OvHV-2 was the likely agent responsible for sporadic, MCF-like vascular disease in sheep.

CASE PRESENTATION

Using similar methods this case study reports on the findings of the first reported cases in an Irish Flock of MCF- like systemic necrotizing vasculitis in sheep associated with OvHV-2. Sheep A, a 16-month-old Texel-cross hogget displayed signs of ill- thrift, Sheep B, a nine-month-old Belclare-cross lamb, was found dead having displayed no obvious symptoms. Both cases occurred on the same farm, however the animals were not related. Lymphohistiocytic vasculitis of various tissues was the predominant histopathological finding in both animals.

CONCLUSION

By combining histopathology, PCR and in-situ hybridisation results, MCF- like systemic necrotizing vasculitis associated with OvHV-2 has been diagnosed for the first time in an Irish flock.

Polyarteritis Nodosa in a Cat with Involvement of the Central and Peripheral Nervous Systems

An 18-month-old neutered male domestic shorthair cat was referred with a history of pyrexia, polyuria and polydypsia, and transient episodes of bilateral hindlimb paralysis. Cardiac evaluation revealed severe systemic hypertension and severe concentric hypertrophy of the left ventricle. One month later the cat had a new episode of hindlimb paralysis with recurrent seizures, and died in status epilepticus. At necropsy examination, the coronary arteries, arcuate renal arteries and common iliac arteries showed marked thickening with nodules segmentally located along the vessels and consequent narrowing of the lumina. Histologically, acute and chronic inflammatory infiltration of the vascular walls was associated with necrosis of the muscular layer. Lesions were consistent with polyarteritis nodosa and involved the small, medium and large arteries of the heart, kidneys, small and large intestine, mesentery, liver and thyroid. Multifocal meningeal vasculitis associated with focal infarction of the frontal lobe and necrotizing vascular polyneuropathy were detected. Involvement of the central and peripheral nervous systems in polyarteritis nodosa is a novel finding in cats.

Systemic Necrotizing Vasculitis in Sheep Is Associated With Ovine Herpesvirus 2

Ovine herpesvirus 2 (OvHV-2) is one of the gammaherpesviruses in the genus Macavirus that can cause malignant catarrhal fever (MCF) in ungulates. Sheep are the adapted host for OvHV-2 and it is generally assumed that infection is not associated with disease in this species. However, cases of "polyarteritis nodosa" or idiopathic systemic necrotizing vasculitis reported in sheep are similar to vascular lesions in clinically susceptible species with MCF. Using a recently developed in situ hybridization (ISH) method, we were able to identify OvHV-2 nucleic acids within lesions and correlate the viral distribution with systemic necrotizing vasculitis in 9 sheep, including both naturally and experimentally OvHV-2-infected animals. ISH, combined with polymerase chain reaction and histology, identify OvHV-2 as the likely agent responsible for sporadic, MCF-like vascular disease in sheep.

Systemic necrotizing polyarteritis in three weaned lambs from one flock

Systemic necrotizing polyarteritis was diagnosed in three 7–11-mo-old lambs from the same flock. Aneurysmal dilation and rupture of the gastroduodenal artery in 1 lamb resulted in fatal hemorrhage. All lambs had severe necrotizing vasculitis involving the small intestine, abomasum, mesentery, kidney, and heart with concurrent lymphocytic enteritis. Immunohistochemistry for T- and B-lymphocytes and macrophages found a T-cell– and macrophage-dominant transmural vascular infiltrate and T-cell–associated enteritis. PCR analysis for pestivirus failed to identify infection in 1 lamb, and more extensive viral microarray techniques applied to the second and third lamb failed to detect viral nucleic acid. The identification of 3 cases within 1 flock raises the possibility of a common etiology; however, no cause was established. A genetic etiology was not considered likely as not all of the lambs were related. The presence of concurrent T-lymphocyte–associated enteritis raises the possibility of an immune-mediated disease process linking the vasculitis and enteric lesions.