In recent studies, it has been shown that DHT (dihydrotestosterone) increases XMRV replication rate threefold. This is not surprising, considering that a number of prostate drugs target this very hormone. Testosterone is metabolized to DHT, which is more powerful - but it is also implicated in pattern baldness, prostate problems, and excess body hair. Some drugs such as Casodex and Flutamide will block DHT at its receptor, however they will result in impaired fertility, loss of libido, and feminization effects, as testosterone is necessary to mitigate the effects of estrogen.
On the other hand, blocking the conversion of Testosterone to DHT should result in a significant drop in viral replication rate. There are 2 very safe drugs that I can think of that can attain this effect: Avodart (dutasteride), and Proscar (available as Propecia in a lower dosage form). A threefold drop in viral replication rate could have a significant effect on symptoms of ME/CFS - It is my opinion that at a certain threshold, the immune system is capable of keeping XMRV in check, hence why XMRV is found in a small number of healthy controls. I would like to see a clinical trial enrolling male patients to test this hypothesis. The effects of these drugs have negligible effects on male fertility - treatment will only produce mild reductions in sperm count averaging 6%. Serum testosterone increased considerably, which is necessary for muscle protein synthesis, regulating the hypothalamus-pituitary axis, and increasing mental and physical energy - all things ME/CFS, Fibromyalgia, and Gulf War Syndrome patients could stand to benefit from.