I'm only 24, and tysabri (natalizumab) has been my miracle drug for ms. But, I've just tested positive for the jc virus. Do I continue? What is next best options?

A matter for your MD. Good question. Is it safe to continue Tysabri (natalizumab) if blood testing for JC is positive? Yes, sometimes. Are there alternative treatments to Tysabri (natalizumab)? Yes, there are good alternatives. The alternatives for you depend a bit on your personal history, such as what worked, and what did not, and perhaps why. Another question is whether confirmatory testing for JC is needed. Hope that helps!
Statistical risks. Tysabri (natalizumab) is a marvelous drug, but has caused over 400 cases of a serious disease called pml. Typically, even with positive blood testing, the disease is not present until about 24 months, and with blood test positivity, the maximum risk would be one in 90. Need to carefully decide options, but many of our patients switch to gilenya, if there is concern about future pml.
See your expert. You need to see an expert given the serious importance of the medications, the diagnoses and the consequences of making any changes based upon a lab study.