Quantitative and Morphological Blood Cell Findings Associated with the Presence of Antigen and/or Antibodies Against Anaplasma phagocytophilum in Sheep.

Abstract

Anaplasma phagocytophilum is the causative agent of a disease known as tick borne fever in sheep, although fever is not always present. Due to inconclusive clinical signs, diagnosis is based on the cytological or molecular detection of the microorganism in blood and/or the determination of antibodies against A. phagocytophilum. The aim of the study was to determine the alterations caused by the presence of antibodies and/or the antigen of A. phagocytophilum in the blood cell count and morphology in sheep. Cytology and indirect immunofluorescence assay were performed for detection of antibodies and the antigen of A. phagocytophilum, respectively. The samples were divided into four groups depending on the result of the antigen and antibody detection. The samples that were only positive for antigen detection had mild anemia, leukopenia (lymphopenia), and thrombocytopenia. The samples that were positive in both assays had anemia, leukopenia (neutropenia and lymphopenia), and thrombocytopenia. Samples that were positive only for antibody detection had mild leukopenia. Morphological findings in infected sheep included band neutrophils, toxic neutrophils, reactive lymphocytes, and activated monocytes. The hematological findings along with cytological and serological tests can contribute to the assessment of the stage of the disease. A combination of leukopenia and thrombocytopenia raises a strong suspicion of the disease. When the microorganism and antibodies are simultaneously present, sheep are more susceptible to secondary complications. The first reported morphological findings and the quantitative hematological alterations are indicative of an inflammatory reaction, antigenic stimulation, and stress.