Fetal Feline Immunodeficiency Virus Is Prevalent and Occult

The feline model of human acquired immune deficiency syndrome, feline immunodeficiency virus (FIV), was used to model maternal-to-fetal human immunodeficiency virus type 1 (HIV-1) transmission. Fetuses were collected from cats infected with clade A FIV(Petaluma) (FIV-A-Pet) and clade C FIV(PaddyGammer) (FIV-C-Pgmr). Virus was detected by DNA polymerase chain reaction (PCR) and a quantitative RNA assay that used substitutional PCR. FIV in tissue sections was assayed by DNA and RNA in situ hybridization and immunohistochemistry. Viral DNA was detected in 67% and 92% of fetuses with FIV-A-Pet and FIV-C-Pgmr, respectively. A discordance was observed between placental and fetal FIV-A-Pet localization. FIV sequestration in fetal tissues was common without detectable virus in blood (occult infection). Viral RNA was not detected in amniotic fluid or fetal plasma. In situ assays demonstrated FIV DNA but neither RNA nor antigens in placentas and fetuses. If mother-to-offspring FIV infection reflects vertical HIV-1 transmission, fetal virus exposure is common and may be occult at term.