Clinical disease resulting from the vertical transmission of Anaplasma marginale has only
been reported on 5 occasions despite studies demonstrating successful in utero transmission.
During the reported experimental induction of congenital anaplasmosis in calves, the
outcome was variable but mostly led to inapparent or mild infection. There are previous
case reports of fatal congenital anaplasmosis following natural infection. The clinical findings
in a 2-day-old calf presented to the Onderstepoort Veterinary Academic Hospital with
clinical signs of congenital anaplasmosis, which was unresponsive to treatment, are described.
Subsequent post mortem diagnostic tests revealed that this calf was co-infected with
bovine viral diarrhoea virus (BVDV). It is postulated that immunosuppression resulting
from BVDV infection predisposed to severe, fatal anaplasmosis in this calf.