Bovine anaplasmosis: in utero transmission and the immunologic significance of ingested colostral antibodies.

Neonate progeny from 3 Anaplasma-free (clean) and 5 Anaplasma-carrier cows were splenectomized and each was challenge exposed with 5 ml of carrier blood. Prepatent times were between 18 and 25 days in calves born of clean cows and between 21 and 36 days in progeny from carrier dams. The lowest packed cell volume values in the clean group occurred at 25 to 39 days after the challenge inoculation and at 29 to 47 days in the carrier group. Highest parasitemias in the clean-calves ranged between 13% and 51% in 25 to 35 days and between 35% to 64% in 38 to 43 days in the carrier calves. Seven splenectomized calves were inoculated with 60 ml of whole blood from progeny of known Anaplasma-free or Anaplasma-carrier cows. After 183 days, all but 1 calf remained free of anaplasmosis. A 1% parasitemia was first observed in that calf 12 days after inoculation with blood from a calf which showed signs of acute anaplasmosis at birth. The infected neonate's dam had recovered from acute anaplasmosis infection during the middle of the second trimester of the gestation. Although not statistically significant, colostral antibodies and/or other maternal factors did not seem to completely protect progeny, but lengthened the prepatent period and delayed anemia and the climax of parasitemia. Further, it was determined that it was possible for an animal affected with acute anaplasmosis before the 190th day of the gestation to transmit anaplasmosis in utero.