Morphologic alterations of Anaplasma marginale in calves after treatment with oxytetracycline.

The morphologic features of Anaplasma marginale were determined after treatment of infected calves with oxytetracycline. By light microscopy, anaplasma bodies in erythrocytes of treated calves were enlarged and vacuolated, small and dense, or comma shaped. Several degenerated forms of anaplasma bodies were observed by electron microscopy. There was a blending of the 2 membranes surrounding initial bodies, aggregation of nucleoprotein at the periphery of the subunit, and vacuolation. A 2nd form of degeneration was coalescence of subunits in marginal bodies. A 3rd form of degeneration was unification of subunits of anaplasma bodies and clumping of nucleoprotein. A 4th form of degeneration was the persistence of an anaplasma body as a solitary, irregularly shaped mass containing electron-opaque clumps.