The most well studied and characterized of the subfamily Betaherpesvirinae is HHV-5, more commonly known as human cytomegalovirus. The descriptive name of viruses belonging to the Betaherpesvirinae subfamily, “cytomegalovirus,” is derived from the characteristic feature of the infection, which is enlarged cells, or cytomegalo. As with many other herpesviruses, HHV-5 is ubiquitous in the human population and largely asymptomatic. However, HHV-5 can be of concern in immunocompromised patients such as transplant recipients and those with acquired immunodeciency syndrome. HHV-5 is also of concern to infected pregnant women as it may cross the placenta and have negative effects on the fetus. As a result, considerable effort has been placed on the development of a safe and effective vaccine for preventing transplacental infections in humans.