It is interesting to see how the current of ideas ebbs and flows, as notions flow like the oceans. Of course some ideas just don’t float for very long at all, but others seem perennial. Some seem locked in endless cycles and every so often they resurface. One of these is the germ theory of disease.
The germ theory related to The Ecological Model of health and disease. Essentially, it reflected the development of medical knowledge up to that point in time when most of the major diseases faced were due to infections. Hence, the notion that if any disease was observed, there must be an underlying infecting organism.
As medical knowledge advanced it became evident that not all disease was caused by infections and the theory ebbed. However, like the ocean tides, it keeps returning as a valid way to describe condition after condition. Note that I am not particularly in favor of the theory because it is too one-dimensional in the clearly multi-dimensional world of health and illnesss but, as I say, it does keep proving correct, even when dismissed.
For example, for many years it was dismissed by medical researchers who were convinced that gastric ulcers were caused by too much stress, poor diet, genetic makeup or anything but an infection. After all, they claimed, no organism could survive the highly acidic stomach environment. However, it turns out that most such ulcers are indeed caused by the infecting organism h. pylori. Of course those other factors can make a person susceptible.
Another example is cancer of the cervix. This condition appears to almost exclusively have a sexually transmitted viral cause. Perhaps it is not too surprising then, that a newly identified virus, tentatively called XMRV, seems to be associated with the development of prostate cancer in genetically susceptible men.
"XMRV is closely related to a virus that causes leukemia in mice and is a newly identified infectious agent in humans. While more research is needed to confirm our findings, this could be the first evidence that a virus is linked to prostate cancer," Dr. Eric Klein of the Cleveland Clinic said in a statement in San Francisco at the 2006 Prostate Cancer Symposium, co-sponsored by the American Society of Clinical Oncology, the American Society for Therapeutic Radiology and Oncology, the Prostate Cancer Foundation, and the Society of Urologic Oncology.
Damage to an antiviral protein called RNaseL, may increase susceptibility to prostate cancer, Klein and colleagues note. Such dysfunction may occur when a gene called HPC1, which produces RNaseL, is mutated and stops functioning normally. Men with these genetic alterations are more prone to prostate cancer.
Klein’s group explored the possibility that a viral infection might contribute to prostate cancer in men with HPC1 mutations that impair function of RNaseL. They used a DNA ViroChip containing the genetic sequences of nearly 5,000 viruses to screen prostate tumor samples from 86 men who had their prostates removed. They compared the incidence of viral infection between men who had two mutated copies of HPC1 gene and men with one or no mutated copies of this gene. Klein and colleagues found XMRV in 45 percent of the 20 men with two mutated copies of the HPC1 gene but in only 1.5 percent of the 66 other men.
XMRV could be sexually transmitted. It’s possible that infection leads to chronic inflammation of the prostate leading ultimately to cancer, the researchers theorize, analogous to the way human papillomavirus (HPV) can trigger cervical cancer.
If the XMRV virus does prove to be a cause of prostate cancer, it could be a therapeutic target for drugs or a vaccine like the new vaccines against cervical cancer currently undergoing approval trials. It would also be one more visitation from the germ theory of disease.
