I've always wondered if it could be xmrv too because I had such a sudden onset. I worked the day before and was fine. I woke up April 16, 1986 with what first felt like the flu or strep throat. By the end of the day I was so sick I was bedridden. Have been in that state for the last 24 years. Antibiotics have helped some. Doctors at first thought viral menengitis, but spinal tap was negative. I just wonder if xmrv is slow to reproduce how I got so sick so fast.
You then get another infection - something probably almost ordinary. It is perhaps a little more severe than normal. The immune system really kicks off. Suddenly XMRV is replicating like made. Twenty years of slow replication take place in just a few days. Viral load in the tissues goes from low to high. Now you have a real case of XAND, as the virus is now able to highly disturb the entire system, triggering major and prolgonged cytokine shifts,...
First you get an XMRV infection, maybe you have it for years with few if any symptoms, like HIV patients. Sudden onset patients then get a nasty virus that speeds up the XMRV-->XAND progression. HHV-6 is a known progression factor for HIV-->AIDS, for example.
You get an XMRV infection which gradually damages your immune system over time. Eventually your immune system is so damaged that you have XAND. Also similar to a path in HIV-->AIDS
This may occur when the virulent 2nd virus hits early in XMRV infection so there's less XMRV to spread (or better immune system function), or perhaps the 2nd virus is not as serious (typical flu) but comes later in the XMRV infection.
XMRV is not HIV. It is different in a number of important ways. But there are some similarities that may be helpful in thinking about XMRV and XAND.
It looks to me like there's plenty of room in the XMRV hypothesis for all the kinds of onset we've seen. It's only when we assume all our symptoms are due directly to XMRV or that XMRV acts like the viruses we're used to (flu, mono, chicken pox) that we run into trouble.
It seems most likely to me that our symptoms are primarily due to secondary infections, which themselves are the result of immune deficiencies caused directly by XMRV. CNS infections, in particular, seem very likely. Several of the herpes viruses can spread to the CNS, especially when not fully suppressed by the immune system.