MATERNAL-FETAL FELINE IMMUNODEFICIENCY VIRUS TRANSMISSION - TIMING AND TISSUE TROPISMS

The feline immunodeficiency virus (FIV) model of vertical human immuno deficiency virus type 1 transmission was used to explore the timing an d tissue tropisms associated with intrauterine lentivirus infection. C ats chronically infected with FIV-B-2542 and their cesarean-derived fe tuses and placentas were assayed by polymerase chain reaction and cocu lture at defined gestational intervals. Prevalence of fetal FIV infect ion was 0 at 3 weeks, 5% at 5 weeks, 38% at 7 weeks, and 60% at 9 week s (term). Fetal tissues exhibiting the highest viral tropism were bloo d mononuclear cells and brain (each containing virus in 60% of FIV-pos itive fetuses) and thymus (47%). Maternal hematologic and virus load m arkers did not vary substantially with gestational stage. Therefore, f etal and/or placental maturation may determine the timing of lentiviru s transmission. FIV infection prevalence in term fetuses was equivalen t to that seen previously in vaginally delivered offspring, suggesting that most vertical FIV transmission occurs late in utero rather than intrapartum.