When scientists are creating tests to detect viruses, they need to balance two factors:
A ‘sensitive’ test is no good if it cross-reacts with other proteins/viruses/antibodies. A test with high ‘specificity’ is no good if you miss 3 out of 10 infections.
Of course, then you need to worry about cost (a perfect test is unusable if no one can afford it) and speed (acute diseases need fast diagnoses, and who wants to wait 3 months to find out if they have a life-altering chronic disease?), and other factors.
So scientists normally use tests that view a putative disease from lots of angles, reducing the odds we are making mistakes by looking for one thing the wrong way–
- Look for antibodies to the virus
- Look for viral antigens
- Look for viral RNA and/or DNA
Each of these tests have variations (antibodies to what? what viral protein? viral genomes? proviruses? which part?), and when you put them all together, the odds of someone being falsely labeled ‘POSITIVE’ (or ‘negative’) drop lower and lower and lower.
One thing about these XMRV ‘tests’ and their reported ‘results’ is that some of the scientists reporting ‘positives’ are not thinking critically, at all, about what they are saying regarding the sensitivity and specificity of their tests.
Prime example, the WPIs latest
bitchfest press release regarding other labs findings (or lack thereof):
6. The UK authors were unable to detect XMRV, even though 4% of healthy individuals were found to be infected in the US. Japanese scientists detected XMRV in 1.7% in healthy blood donors in Japan.
This statement is completely and utterly misleading to the general public. Comparing these results is comparing apples to oranges.
The WPI found 8 of 217 (3.7%) of their healthy controls were PCR positive for the gag gene. Only 11 healthy controls were PCR tested for both the gag and env gene. Only one person was gag positive (9%), none env (0%), 0 out of 16 (0%) healthy controls expressed viral antigens on white blood cells, 0 out of 5 (0%) had viral antigens by Western blot, 0 out of 12 (0%) had cells that could produce infectious virus, 0 of 7 (0%) of healthy controls made antibodies to XMRV.
If we are going to compare apples to apples, we need to compare the WPIs antibody results with the Japanese antibody results.
In healthy controls:
WPI: 0 of 7 (0%)
Japanese group: 5 of 300 (1.67%)
We can then compare these two results to the Second British paper, which also looked for antibodies in healthy controls:
UK #2: 25 of 395 (6.33%)
Ummm… so, technically, the second British group found more ‘XMRV’ than the other two groups, including the WPI. But they dont believe their results.
Know who I believe?
Us PhDs have lots of tricks for detecting a virus in the lab, and individual PhDs might want to see/not want to see certain viruses (**WINK!!**) but Big Pharma doesnt give a shit. If the virus exists and is a threat to humans/agriculture/whatever, Big Pharma will industrialize our lab ‘tricks’ and turn them into large-scale diagnostic tests with error rates (false positive/false negative) numbers as low as physically possible. I mean, there is a reason every kit I buy has in big letters “FOR RESEARCH USE ONLY!” “NOT FOR CLINICAL USE!” etc.
Big Pharma has this shit covered in clinical labs.
Turns out Abbott Diagnostics (the makers of OxyContin!) has been working with Emory to create a reliable XMRV detection system. They screen blood for antibodies to three XMRV proteins: gag p30, env gp70 and env p15E. Their results from screening the general population in the US?
Abbott: 3 of 2,851 (0.1%)
I believe that. Not only because of their stringent ‘positive’ guidelines and 100% sensitivity in detecting antibodies in animal models, but because that number, 0.1%, makes sense.
HIV-1, a big deal, is found in about 0.3% of the US population.
0.1% for XMRV in the general population makes a hell of a lot more sense for a brand new blood-born/STD retrovirus than 4%, 1.7%, or 6.3%.
This tiny number does reinforce my suspicions that XMRV doesnt transmit via saliva, though.
And then theres that pesky fact that XMRV has not been established as a causal factor for any human disease.