Congenital Rift Valley fever in Sprague Dawley rats is associated with diffuse infection and pathology of the placenta
Rift Valley fever (RVF) is a disease of animals and humans associated with abortions in ruminants and, more recently, late-gestation miscarriages in African women. Here, we use a rat model of congenital RVF to identify cellular tropism, pathology, and local immune responses occurring in the placenta during vertical transmission. Infection of pregnant rats during late gestation (embryonic day 14) resulted in vertical transmission to the placenta and widespread viral infection throughout the decidua, basal zone, and labyrinth zone. Some pups delivered from infected dams appeared normal while others had gross signs of teratogenicity including fetal death. Histopathological lesions were detected in placenta from pups regardless of teratogenicity, while teratogenic pups had more widespread hemorrhage throughout multiple placenta layers. Teratogenic events were also associated with significant increases in pro-inflammatory cytokines, type I interferons, and chemokines within the placental tissue. Thus, we found that RVFV displays a high degree of tropism for all placental tissue layers, and that the degree of hemorrhage and inflammatory mediator production is highest in placenta from pups with adverse outcomes. This is the first detailed pathological study of the mechanisms of RVFV infection of placental tissue in a tractable rodent model of congenital RVF disease.