Experimental fetal and transplacental Neospora infection in the nonhuman primate

BACKGROUND: Neospora is a newly recognized Toxoplasma-like protozoan that causes spontaneous abortion and/or neonatal disease in a wide range of animals. The purpose of this study was to determine the susceptibility of primates to Neospora infection. EXPERIMENTAL DESIGN: In experiment 1, two rhesus macaque fetuses were inoculated in utero at gestational day 65 with 1 x 10⁶ culture-derived Neospora tachyzoites. A control fetus was given uninfected vehicle. The fetuses were removed by hysterotomy between 13 and 22 days postinoculation. In experiment 2, two pregnant macaques were inoculated intramuscularly and intravenously on gestational day 43 with a total of 1.6 x 10⁷ culture-derived tachyzoites. A pregnant control macaque was given uninfected vehicle. The fetuses were removed by hysterotomy between 67 to 70 days postinoculation. Fetal tissues were collected for in vitro parasite isolation, histopathology, and Neospora immunohistochemistry. Fetal blood was examined for Neospora-specific antibody titers using an indirect fluorescent antibody test. RESULTS: Neospora infections were confirmed in all fetuses that received tachyzoites either directly or via transplacental infection. In experiment 1, infected fetuses had reduced amniotic fluid volumes, marked protozoal amnionitis and dermatitis, and a mild multifocal encephalitis. Infected fetuses from experiment 2 had a chronic multifocal necrotizing nonsuppurative meningoencephalitis with microcavitation, that was confined to the cerebrum, and a mild multifocal necrotizing amnionitis. In both experiments, Neospora tachyzoites were detected in association with lesions in fetal tissues by immunohistochemistry, and the parasites were reisolated in vitro. IgG Neospora antibody titers were detected in blood from all infected fetuses, whereas Neospora-specific IgM and IgA titers were found in one and three fetuses, respectively. CONCLUSIONS: Results indicate that nonhuman primates are susceptible to transplacental Neospora infection. The fetal lesions after transplacental infection are similar to those induced by transplacental Toxoplasma infections in primates.