Anaplasma marginale infection in a cow


The anemia in this cow (which is severe, HCT of 12%) is non-regenerative (no polychromatophils or macrocytes), likely due to an acute onset. Anaplasma causes extravascular hemolysis. The organism resembles Howell-jolly bodies (micronuclei, nuclear remnants) and can be difficult to differentiate from these nuclear fragments. However, the lack of regeneration in this animal argues against Howell-jolly bodies, they are more variable in size and there are multiple organisms in a single cell. The latter two findings would be unusual for nuclear remnants.