A new study has found that a retrovirus that originated in mice and attacks the human immune system is found in 68% of people diagnosed with chronic fatigue syndrome, but only 4% of healthy control subjects. This implies that there are something like 12 million asymptomatic or undiagnosed XMRV carriers out there, in addition to two-thirds of the 1-4 million people who have chronic fatigue syndrome. This suggests that millions of people have XMRV for years that only produces chronic fatigue syndrome after stress, a weakened immune system or something else allows the XMRV to take hold.
Only six kinds of human retrovirus had previously been discovered. Two types of HIV (HIV-1 and HIV-2 discovered in 1983 and 1986 respectively) which cause AIDS, and four kinds of HTLP which causes a rare, highly lethal form of leukemia that impacts T-cells (one in 1977, one in the 1980s, and two in 2005). Both retroviruses have long periods of dormancy. Untreated HIV typically doesn't cause death for a decade. About 4-5% of people with HTLP will eventually develop the associated form of leukemia; about 1 in 1500 carriers develop the associated form of leukemia each year. There are about 75,000 HTLP carriers in the United States right now. Both HIV and HTLP are far more common among IV drug users and among African-Americans than in the general population in the United States.
XMRV is in the same genus of retroviruses as the feline leukemia virus, which is well known because house cats are routinely immunized against it. Indeed, the existence of a feline leukemia virus vaccine offers hope that an XMRV vaccine may someday be developed. Vaccination may be a more attractive option for XMRV than for HTLP which is quite rare, or HIV, for which it has been notoriously difficult to create an effective vaccine. The first successful HIV vaccine test conducted in Thailand was announced this year, but it worked only about a third of the time.
Chronic fatigue syndrome has historically been a diagnosis obtained only by ruling out all other possibilities. Now, a blood test will be able to quickly identify people who are XMRV positive, leading to quick diagnosis and more focused treatment for two-thirds of sufferers, who have historically faced great skepticism from the medical establishment and seen treatment delayed to their detriment during prolonged periods of diagnosis. Some members of the medical establishment have seen chronic fatigue syndrome as a form of hypochondria or mass hysteria, and in the case of XMRV positive patients, that attitude will evaporate. The discovery will also suggest many strategies used to deal with HIV like control of viral transmission via blood or sexual transmission, and blood supply screening. XMRV carriers may also be prime candidates for efforts to boost their immune systems and limit stress in order to prevent the XMRV infection from giving rise to full blown chronic fatigue syndrome. But, a positive XMRV test could cause chronic fatigue syndrome to be viewed by a health insurance company as a pre-existing condition that will not be covered when, and if, it emerges.
The situation could also increase skepticism from the medical establishment for XMRV negative patients.