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.