Transplacental infection of a foal with Anaplasma phagocytophilum

This is the first report to document transplacental transmission of Anaplasma phagocytophillum in the horse. A 4-year-old late-term pregnant mare presented for a recent onset of pyrexia due to equine granulocytic anaplasmosis (EGA). She was hospitalised for treatment with oxytetracycline and monitoring of high-risk foaling due to significant thrombocytopenia. Parturition occurred overnight, and the foal was PCR positive for A. phagocytophilum at birth. The foal was slow to stand and nurse, with signs of neonatal encephalopathy and anaplasmosis (thrombocytopenia). Therapy with oxytetracycline resulted in complete clinical recovery of the mare and foal within 5 days. Congenital anaplasmosis should be considered in any foal delivered to a mare suffering from EGA during late-term pregnancy and guide appropriate antimicrobial therapy.