The similarity of MLVs to HIV immediately leads one to think that they are probably transmitted similarly, ie. blood transfusions, sexual transmission from person to person, etc. However, CFS does not have the epidemiological characteristics of HIV. It seems to be fairly rare across spouses, and if it occurs in families it seems more likely to be among children and perhaps a parent. Also, most of the people with CFS that I know never knew anyone else with the illness before they got it, including myself. In fact, before I got CFS I had never heard of anything about it, and this seems pretty typical (It always amazed me how anyone could think this illness was psychological with large numbers of people coming up with the same set of chronic symptoms - sore throat, swollen lymph nodes, debilitating fatigue, difficulty with sleep, foggy thinking, tinnitus, aching joints, funny heart beats, etc - with a sudden onset and never having communicated with anyone else with those same symptoms). Anyway, this morning I was thinking, it seems there are so many varieties of MLVs (4 polytropic groups plus one xenotropic XMRV so far), that it would be odd for them to all derive from the same mouse to human transmission some decades or so ago. That coupled with the fact that the polytropic MLVs are infectious both to mice and humans lead me to think: what if MLVs were not transmitted to humans decades ago and then transmitted human to human the way HIV is, but were currently being transmitted primarily from mice to humans much the way the hantavirus is, say from mouse dropping that dry, become dust and are later inhaled by humans, or maybe instead via a mouse to human vector such as fleas. Such a mode of transmission would help account for the odd epidemiological characteristics. Transmission would often be sporadic, without the usual human to human transmission characteristics. Clustered outbreaks would occur when groups of mice became ill by transmitting to each other and then transmitting it to humans in the community. Members in a family would be more likely to get ill if the household had mice infected with the illness. Once humans are infected, blood transfusions could become a source of secondary transmission.