With the vast focus on European diseases, Native American diseases have been largely ignored, to the point where it’s commonly misconstrued that native peoples were either disease free, or the diseases were mild and unimportant to study.
This is, of course, completely inaccurate.
How inaccurate is this? Well, let’s take syphilis as an example.
Syphilis is a multi-staged sexually transmitted disease caused by the bacterium Treponema pallidum. It starts off with genital sores and then progresses into skin rashes (typically on the palms and bottoms of feet) and mucous membrane lesions, with the possibility a whole host of other symptoms (including, but not limited to, fever, swollen lymph glands, condyloma lata, sore throat, fatigue, muscle aches, and hair loss). So far, so unpleasant. Don’t worry though, it gets worse. These are just the symptoms of the primary and secondary stages of the disease, all of which will go away on their own. However, if the disease is left untreated, it will progress into a latent stage, in which it can lie dormant for years before entering a late stage infection. Late stage syphilis “may damage the internal organs, including the brain, nerves, eyes, heart, blood vessels, liver, bones, and joints.”  (Incidentally, late stage syphilis’ propensity to damage bones is why we can identify syphilis via skeletal remains).
This is probably sounding (and looking) pretty gross by now, right? Well, the good news is that nowadays we can treat readily syphilis infections with penicillin. Back in the 1500s though? Not so much.
In 1495, and epidemic of syphilis began in Europe when the French army of Charles the VIII invaded Italy and kicked off the spread of the disease. From there it spreads all through Europe, into North Africa, and as far out as India (I highly recommend reading through the amazing amount of finger pointing that went on during the epidemic). 
Now, you might be wondering where the Americas come into play when this is a European epidemic. Well, here’s a hint (if you missed it before), take another look at the year the epidemic began. Now, add to that the fact that syphilis had never been seen among Europeans until that first epidemic.
Although there has been much debate about the origins of syphilis in Europe, the most compelling hypothesis is that Columbus brought the disease back with him from his voyage to the Americas. Although reports of several of Columbus’ crew suffering from symptoms of syphilis upon their return to Europe and accounts of Native Americans having elaborate treatments for the disease (whereas Europeans had never seen it before) do point to an American origin for syphilis, there was still much backlash against the idea that the disease could have been brought to Europe from the Americas. 
The main source of evidence for an American origin of syphilis is in the skeletal records of both the Americas and Europe. As I mentioned before, late stage syphilis can cause bone deformities that result in characteristic lesions that can be observed on the skeleton of the infected deceased.
Now, there is plenty of skeletal evidence in the Americas that the disease had been present there for thousands of years. On the other hand, there was very little evidence of syphilis’ presence in Europe’s skeletal record before Columbus’ voyage. In fact, there were only 16 bone fragments that could be definitively linked to syphilis infections and had been carbon dated back to before Columbus’ voyage. However, all of these bone fragments were found in coastal locations that were heavily reliant on seafood; which contained carbon brought up from deep in the ocean and has been known to interfere with accurate carbon dating. If this inaccuracy is adjusted for, none of the bone fragments date to pre-contact with the Americas. 
This evidence (and lack thereof) points to a scenario where Columbus and his crew made the journey to the Americas, managed to contract syphilis, and returned with it to Europe. Once there, it swept through the population and gave the Europeans a little taste of their own medicine. How’s that for a non-virginal soil epidemic!
By Taylor Hellmann