CMV- cytomegalovirus

I have a couple questions about CMV-cytomegalovirus as there is a general lack of information about this virus. I am curious about its transmission.
From what I understand, it is typically transmitted in children from fluid exchange, but i am also reading that it may be transmitted through sexual contact. My questions:

1) How easy is it to transmit CMV through sexual contact?
2) Does an adult have to have an active infection to transmit the virus?
3) How long do active CMV infections last in adults?
4) If in latency, what is the risk of transmitting CMV to others? Is prolonged exposure (ie-alot of kissing, sexual contact) necessary? Or is a one time exposure all that is necessary?
5) How easy it is to pass in only oral sex? Or is kissing a more common route of infection?

[H. Hunter Handsfield, M.D.]

CMV is pretty complex topic, although almost always an entirely benign infection that we all get at one time or another.  So the main message is one of reassurance and don't worry about it.  Partly for that reason, I'm going to answer your specific questions very succinctly.

1) It's easy, if one misses out on childhood infection.  That is, adults who didn't get CMV as kids therefore aren't immune to it when they become sexually active, and often acquire the virus sexually.

2 and 3) CMV is a lifelong infection; once you have it, it persists for life.  How infectious it is during most of that time isn't known.

4) Not known.  The virus probably isn't consistently in genital secretions or saliva during longstanding latent infection, but might reappear and be transmissible intermittently.

5) The actual mechanisms - i.e., sexual practices - of sexual transmission of CMV have not been well studied.  Probably mostly by vaginal or anal intercourse, but the potential roles of kissing or oral-genital contact have not been carefully studied.

The biggest problem for CMV is when a pregnant woman catches her first infection during pregnancy; serious infections of the newborn can result.  At present, there is no realistic way to prevent sexual transmission of CMV or fetal infection.  Fortunately, serious outcomes are rare (although the importance of milder fetal or neonatal CMV infections is a matter of debate and uncertainty).  Research on vaccines has been going on for 2-3 decades, so far without notable success.

Good luck--  HHH, MD