Cytomegalovirus (CMV) - a herpesvirus (species Human herpesvirus 5 of the genus Cytomegalovirus) that in healthy individuals casus an infection that is asymptomatic, or is accompanied by mld symptoms (as fever or fatigue) but in immunocompromised individuals and newborns may cause an infection marked by serious, sometimes life-threatening symptoms (as pneunomia, hepatitis, retinitis, brain inflammation, or seizures) - Merriam-Webster

Cytotoxic - Toxic to cells. - Merriam-Webster

Herpesviruses - A large family of DNA viruses that cause diseases in animals, including humans. At least five species are extremely widespread in humans: HSV-1 and HSV-2 cause orolabial herpes and genetial herpes; varicella zoster virus causes chickenpox and shingles; Ebstein-Barr virus is implicated in several diseases, including mononucleosis and some cancers; and cytomegalorvirus. More than 90% of adults have been invected with at least one of these, and a latent form of the virus remains in most people. - Wickipedia

Immunocompetence - The ability of the body to produce a normal immune response following exposure to an antigen. Immunocompetence is the opposite of immunodeficiency or immuno-incompetent or immuno-compromised. - Wikipedia

Immunocompromised - Having the immune system impaired or weakened (as by drugs or illness). - Merriam-Webster (Note: Infants are immunocompromised by virtue of their immune systems being undeveloped.)

Nephrotoxic - Poisonous to the kidney. - Merriam-Webster

Nucleoside - Any of several compounds that consist of a ribose or deoxyribose sugar joined to a purine or pyrimidine base and to a phosphate group and that are the basic structural units of nucleic acids such as RNA and DNA. - Merriam-Webster

Nucleotidyltransferase - any of several enzymes that catalyze the transfer of a nucleotide residue from one compound to another.

Polymerase - Any of several enzymes that catalyze the formation of DNA or RNA from precursor substances in the presence of preexisting DNA or RNA acting as a template. DNA polymerase - any of several polymerases that promote replication or repair of DNA usually using single-stranded DNA as a template. - Merriam Webster

Tropism - Involuntary orientation by an organism or one of its parts that involves turning or curving by movement or by differential growth and is a positive or negative response to a source of stimulation. - Merriam-Webster