EXPERIMENTAL REPRODUCTION OF BOVINE FETAL NEOSPORA INFECTION AND DEATH WITH A BOVINE NEOSPORA ISOLATE

Studies were conducted to determine the pathogenic potential of the re cently isolated bovine Neospora protozoa (BPA-1) for the bovine fetus. Cows chosen for study had Neospora titers < 160 using an indirect imm unofluorescent antibody (IFA) test, Four experimental groups were stud ied. In group 1, 2 fetuses were inoculated in utero at 118 days gestat ion with culture-derived Neospora tachyzoites. A pregnant control cow was housed in the same pen. observed daily and screened serologically for evidence of exposure to Neospora. In group 2, 2 cows were infected with Neospora tachyzoites at 138 or 161 days gestation, and 1 control cow was given uninfected cell culture suspension simultaneously at 15 4 days gestation. Groups 3 (85 days gestation) and 4 (120 days gestati on) each consisted of 2 cows infected with Neospora tachyzoites and 1 control cow given uninfected material at the same stage of gestation. Dead fetuses were surgically removed from the infected cows in group 1 on postinfection day (PID) 17. The histopathology was compatible with protozoal fetal infection, and protozoa were identified by immunohist ochemistry. Viable fetuses were removed surgically from cows in group 2 on PID 28-30. The histopathology was compatible with protozoal fetal infection, protozoa were identified by immunoperoxidase techniques, a nd Neospora tachyzoites were reisolated in vitro from tissues of the 2 infected fetuses. In groups 3 and 4, the control fetus and 1 infected fetus were removed surgically between PID 26 and PID 33. The remainin g infected cows were observed until fetal death or abortion occurred. In group 3, the fetus that was surgically removed from 1 infected cow had no pathologic abnormalities, and parasites were not found (PID 26) . The second fetus in group 3 died in utero, and expulsion of a mummif ied fetus was induced on PID 67. Brain histopathology was compatible w ith protozoal infection, and parasites were identified by immunoperoxi dase techniques. The fetus that was surgically removed (PID 32) from 1 infected cow in group 4 had lesions compatible with protozoal infecti on, and Neospora tachyzoites were reisolated in vitro from fetal tissu es. The second infected cow in group 4 produced a full-term live calf that had a precolostral Neospora titer of 20,480. Clinically, this cal f had depressed conscious proprioception in all limbs. Very mild lesio ns were found in the central nervous system, but protozoa were not fou nd in the tissues. The results demonstrate that the bovine Neospora pr otozoa can be transplacentally transmitted, resulting in fetal infecti on and death, and mimics the naturally occurring fetal disease.