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The Development of a Semi‐automated Latex Agglutination Test for the Detection of Antibodies to Anaplasma marginale Using a Cell Culture‐derived Antigen

ABSTRACT: Serologic diagnosis of anaplasmosis is currently done by the complement‐fixation, ELISA, and card agglutination tests. These tests have utilized A. marginale harvested from bovine erythrocytes as antigen which is often contaminated with erythrocyte stroma. We are currently testing A. marginale propagated in a Ixodes scapularis cell line as antigen for serologic tests. In this study, we report the use of the cell culture‐derived A. marginale as antigen for development of a rapid, semi‐automated latex agglutination test. Diluted serum and latex (polystyrene microspheres), sensitized with cell culture‐derived A. marginale proteins, were dispensed into 96‐well microtiter plates. An initial reading of light transmission was recorded by a computer‐interfaced scanning autoreader. After 30 minutes, the plates were mixed and read a second time, recording the delta % light transmittance. The sensitized latex microspheres (latex) agglutinated in the presence of A. marginale antibodies, thus producing an increase in light transmittance. In preliminary tests, 724/977 of the sera were positive for A. marginale antibodies with an apparent agreement of 83.3% when compared with the complement‐fixation test. Sensitization and sera dilution buffers were shown to have a marked effect on the sensitivity and specificity of this assay. Results will be presented on the optimization of buffers and the testing of sera from experimentally and field‐infected cattle.