XMRV 

also becoming known as HGRV - human gamma retrovirus

Xenotropic murine leukaemia virus - a retro virus first discovered in 2006.

Possible involvement of this virus in Lyme, CFS and other degenerative neurological disorders.
Is this the missing link explaining why some people with Lyme Disease deteriorate so badly? This question will undoubtedly be answered in the near future.

Here are some relevant links:

http://lookingatlyme.blogspot.com/2010/02/xmrv-mecfs-lyme-disease.html

http://www.cheneyresearch.com/topic/xmrv

http://vesta.cumc.columbia.edu/lymedisease/news/user/featNews.php?sel=newsFeat sixth topic down the page

http://en.wikipedia.org/wiki/Xenotropic_murine_leukemia_virus-related_virus 

December 2010 updates on XMRV

Spread of the retro virus http://dancingwiththesandman.blogspot.com/2010/12/unintended-international-spread-of.html

More to come proving it is not a contaminant (recently published articles suggested this) - see next entry

New 2011 Information:

The presentation given in this update on XMRV by Dr AzRa Mael, MD 
gives important recent information that starts to tie the threads together
http://campaign.r20.constantcontact.com/render?llr=ie78sucab&v=001XMg27mzAweqsyzjqF49USomtrkOHsayt41QD3ZlGi9g1J4QFqPv4ghU8sIlrnk1T7x9HR7OsKFLT9LiDhMlSHFuWJt2qxJP-ToknNH0j8IIRxpnaGuQlRQ%3D%3D