GC: adj

S: NIH – https://www.nlm.nih.gov/medlineplus/viralinfections.html (last access: 1 September 2015); WebMD – http://www.webmd.com/a-to-z-guides/bacterial-and-viral-infections (last access: 1 September 2015).

N: 1. “of the nature of, or caused by, a virus,” 1944, see virus + -al (1). Sense of “become suddenly widely popular through Internet sharing” is attested by 1999, originally in reference to marketing and based on the similarity of the effect to the spread of a computer virus. Related: Virally.
2. First Known Use: 1937.
Full Definition:

• of, relating to, or caused by a virus
• quickly and widely spread or popularized especially by person-to-person electronic communication .

S: 1. OED – http://www.etymonline.com/index.php?term=viral (last access: 1 September 2015). 2. MW – http://www.merriam-webster.com/dictionary/viral (last access: 1 September 2015).

SYN:
S:

CR: antiretroviral therapy, virus.