BK virus can infect and result in kidney allograft (transplanted) dysfunction, prevalence rate being around 5% within 10-12 months after having received the transplant, though it can occur much sooner as in your case. After the diagnosis of BK virus disease or the nephropathy in the transplanted kidney, first line of approach is to reduce the immunosuppression by cutting back on the dosage of various immunosuppressive medications. If the kidney function doesn't improve over a period of few weeks to months, then one would be treated with antiviral agents against the BK virus. There is no definite set of antiviral drugs known to be effective against the virus. You would require close monitoring of your kidney function over next several months to begin with under the supervision of your nephrologist. Unfortunately, the reported incidence rate for transplanted kidney's failure from BK virus nephropathy is around 15-40%.