Morphologic Lesions, Hematological and Immunological Responses and Neutrophil Functions in Fetal, Neonatal and Adult Sheep Infected With Brucella Abortus.

Fetal, neonatal and adult sheep were infected intramuscularly with B. abortus Strain 2308. Morphologic lesions were present in the regional lymph nodes of B. abortus infected neonatal and adult sheep and in the regional lymph nodes, lungs and the parietal surfaces of thoracic and abdominal organs of B. abortus infected fetuses. The regional lymph nodes of neonatal and adult sheep were moderately to markedly enlarged and contained prominent lymphoid follicles and few to numerous plasma cells. Fetal lesions were characterized by: lymph nodes with sinuses that contained numerous foamy macrophages, pneumonia and fibrin covered thoracic and abdominal organs. Fetuses responded to B. abortus infection with a neutrophilia, lymphopenia and occasional monocytosis. Neonatal and adult sheep did not have significant hematological responses to B. abortus infection. An antibrucella antibody response was not present in fetuses but adult and neonatal sheep produced brucella specific antibodies as early as PI day 8. Fetal neutrophil phagocytic but not killing function against B. abortus and S. aureus was enhanced by B. abortus infection. Neonatal phagocytic and killing functions against B. abortus were increased by B. abortus infection while only phagocytic function against S. aureus was increased. Adult sheep phagocytic and killing functions were not altered by B. abortus infection. Fetal serum cortisol levels were markedly elevated by B. abortus infection. B. abortus Strain 2308 produced morphologic lesions, hematological, immunological and cortisol responses and increased neutrophil functions in sheep. Because most of these changes are similar to those reported in cattle, sheep, especially during fetal development, could serve as an experimental model for bovine brucellosis