Foot-and-Mouth Disease Virus Crosses the Placenta and Causes Death in Fetal Lambs

Abstract

Eighteen pregnant sheep, six at 45 days gestation and twelve at 75 days gestation, were infected with foot-and-mouth disease virus (FMDV) type O UKG 34/2001. Two sheep from each gestational group were killed at 2, 4, and 7 days post-inoculation (dpi). Three sheep, pregnant for 75 days at infection, were killed at 17 and 18 dpi. Real-time reverse-transcriptase polymerase chain reaction (RT-PCR) and virus isolation (VI) were used to detect viral RNA and infectious virus, respectively, in fetal tissues taken post mortem. Eleven fetuses were obtained from the six sheep inoculated at day 45 of gestation. Of these, two of three fetuses at 2 dpi had viral RNA detected by RT-PCR and virus was detected in one by VI. Viral RNA was detected in two of four fetuses at 4 dpi, while viral RNA and virus were detected in all four fetuses at 7 dpi. No gross abnormalities were evident in these fetuses. In the group inoculated at day 75 of gestation, viral RNA was detected in three of four fetuses at 4 dpi. Virus and viral RNA were detected in three of four fetuses at 7 dpi. Of the seven fetuses examined at 17 and 18 dpi, viral RNA was detected in five, and four of these had died in utero. Gross abnormalities including haemorrhage and oedema in a number of tissues were evident in many of the fetuses in this group, but no vesicular lesions were found. Viral RNA and virus were detected in the amniotic fluid associated with infected fetuses. This study is the first to demonstrate that FMDV may cause transplacental infection and fetal death.