A Review of Emerging Viral Pathogens and Current Concerns for Vertical Transmission of Infection

Vertical transmission, or mother-to-child transmission, of bacterial, viral, or parasitic infection is rare due to the success of the barrier functions of the placental maternal-fetal interface, which provides physical, molecular, and immunological mechanisms to protect the developing fetus. Infections in pregnancy that can cross the placenta and reach the fetus can cause fetal loss, stillbirth, or prematurity or can lead to congenital infection, malformation of organs, and neonatal disease at birth. The acronym TORCH stands for Toxoplasma gondii, other, rubella, cytomegalovirus, and herpes simplex virus (HSV). Within the TORCH category of 'other,' there are increasing emerging viral pathogens that can pass from mother to fetus, including Ebola virus, Zika virus, and emerging arbovirus infections, including West Nile virus and Rift Valley fever virus. Although SARS-CoV-2 has rarely been reported to show transplacental spread, the recent COVID-19 pandemic has highlighted the importance of surveillance of new human pathogens with rapidly evolving transmission patterns. This article reviews the protective roles of the placental maternal-fetal interface, the concept of TORCH infections, and the emergence of viral pathogens currently causing concerns for vertical transmission from mother to fetus.