Ovine anaplasmosis: in utero transmission as it relates to stage of gestation.

Seventeen mature, pregnant, anaplasmosis-susceptible and 3 anaplasmosis-carrier ewes were used in Anaplasma ovis in utero transmission studies. Susceptible ewes were arbitrarily allotted to 3 groups, 4 each in groups A and C and 9 in group B, and were inoculated with whole blood from a carrier ewe. Each group was Anaplasma-exposed once during one of the thirds of pregnancy. In all ewes, resulting parasitemias were low and anemias were mild. Three carrier ewes comprised group D. Blood samples were obtained once during gestation from each fetus at various stages of development for evaluation and inoculation into splenectomized lambs. Blood obtained from neonates before nursing was also evaluated for Anaplasma presence. Parasitemia was not detected in any fetus or neonate; however, 3 of 16 splenectomized lambs inoculated with fetal or neonate blood developed acute anaplasmosis. Dams of fetuses/neonates with infective blood had been Anaplasma-exposed during their 2nd or last 3rd of pregnancy. Infective Anaplasma agents crossed the placental barrier as early as 130 days of gestation.