Clinical chemistry of anaplasmosis: blood chemical changes in infected mature cows

The clinical chemical changes induced by Anaplasma marginale infection were determined in 16 adult, intact cows infected with either of 2 virulent isolates and in 8 others treated with a live sheep-attenuated A marginale vaccine and were compared with the clinical chemical analyses in 7 noninfected controls. Blood samples from the cows were analyzed for various serum components and during clinical disease. Cows infected with the 2 virulent isolates had maximum erythrocyte parasitemias (0.5% to 66%) between 1 and 11 days of patency (DP); 7 of the 16 infected animals died within 5 to 12 DP. Cows given the sheep-attenuated anaplasma vaccine had maximum parasitemias (0.1% to 4.2%) between 1 and 16 DP and none died. Infection with the virulent isolates produced severe anemia (mean RBC count = about 2 million/mm3) and caused increases in serum total bilirubin (TBILI), direct bilirubin (DBILI), serum urea nitrogen (SUN), alkaline phosphatase (ALP), and serum aspartate aminotransferase (AST) that were significantly higher than comparable changes in control values. These increases were highest after peak parasitemias in surviving animals. Vaccination with the attenuated isolate produced a mild anemia (mean RBC count = about 5 million/mm3) and a significant increase only in ALP. Marked increase in TBILI, DBILI, SUN, ALP, and AST were detected 0 to 1 day before death in 3 cows. However, such increases were not observed 2 to 4 days before death in the other cows that died.