Final answer:
Cytomegalovirus (CMV) is the virus most threatening to the fetus and neonate because it can cause significant long-term health problems if it infects the developing fetus.
Step-by-step explanation:
Among the viruses listed, Cytomegalovirus (CMV) is considered the most threatening to the fetus and neonate. CMV can cross the placenta and cause serious complications such as developmental delays, hearing loss, and visual impairments. While many CMV infections are asymptomatic, in fetuses and newborns, the virus can lead to significant long-term health problems. Other viruses like Herpes simplex virus (HSV) can also cause serious conditions like neonatal herpes, which is risky for newborns especially when the mother contracts HSV for the first time during pregnancy. However, CMV is specifically known for its potential to cause congenital conditions and is a major focus of prenatal screening due to this.