After kidney transplantation, long-term immunosuppressive drugs are required and the immunity of the body will be reduced, after which the viruses present in the body may be activated, resulting in damage to the body. One particular type of virus is BK virus. Unlike other viruses such as cytomegalovirus, EBV and herpes virus, this virus mainly causes damage to the kidney and can directly affect the survival of the transplanted kidney. Therefore, damage to the transplanted kidney caused by BK virus after transplantation is an important factor affecting the survival of the transplanted kidney and deserves your attention. BK virus originated in a kidney transplant patient whose initials were BK. The presence of this virus was first confirmed in this patient in 1971, and similar cases have been found in many transplant centers in the United States since then. BK virus nephropathy has also been reported in China in recent years. About BK virus nephropathy from the following aspects to make some elaboration for you: 1. Under what circumstances can BK virus nephropathy occur? Many people will ask, under which circumstances BK virus nephropathy can occur after kidney transplantation? There is no clear answer. Many recipients started to take immunosuppressants when they were treated for kidney disease before kidney transplantation, causing immune deficiency. It has been reported that BK virus nephropathy can also occur in kidney disease patients who have been taking immunosuppressive drugs for a long time, suggesting that immune depression due to immunosuppressive drugs is a major factor leading to BK virus nephropathy. The prevalence of BK virus nephropathy has been on the rise in the last decade and is strongly related to the current strong immunosuppressive drugs and strong preoperative immune induction. Some statistics show that the incidence of BK virus nephropathy is high in kidney transplant recipients taking tacrolimus combined with mycophenolate and prednisone because this combination has the strongest immunosuppression. The incidence was lower in recipients on other immunosuppressive combinations such as cyclosporine in combination with mycophenolate mofetil. Therefore, for patients who are immunocompromised before surgery it is recommended to check urine or blood for BK virus replication before kidney transplantation, and if the virus replicates before surgery, an immunosuppressive regimen with weaker immunosuppression is recommended. 2. How to monitor post-operative BK virus With the gradual awareness of BK virus nephropathy after kidney transplantation, many transplantation centers are regularly monitoring BK virus after kidney transplantation to monitor BK virus replication in blood and urine. Those patients with significant viral replication are promptly adjusted for immunosuppression to avoid BK virus-induced nephropathy and to provide early prevention. Therefore, for hospitals that have the conditions, BK virus replication levels in blood and urine should be routinely checked regularly after kidney transplantation, and then early intervention should be made according to the viral replication. For some high-risk patients, even if the hospital is not equipped to monitor, if abnormal transplant kidney function occurs, it needs to be measured at a transplant center that can monitor BK virus replication to assist in determining the cause. It is currently recommended that BK virus replication in blood and urine be monitored once a month for 3 months after kidney transplantation and once every three months to 1 year after surgery. 3. How to diagnose BK virus nephropathy BK virus nephropathy tends to occur within 1 year after kidney transplantation, so you need to consider whether you have BK virus nephropathy when you have elevated blood creatinine within 1 year after surgery. Elevated BK virus replication in the blood or urine can only be described as BK virus blood or urine disease, which does not equal BK virus nephropathy and does not necessarily result in transplant kidney function impairment. The current diagnosis of BK virus nephropathy relies on a transplant kidney biopsy. The diagnosis of BK virus nephropathy can only be confirmed by special examination of the kidney tissue from the puncture. The vast majority of patients diagnosed with BK virus nephropathy will have elevated blood creatinine, and some patients will have hydronephrosis in the pelvis of the transplanted kidney, which will help to confirm the diagnosis of BK virus nephropathy. 4, how to treat BK virus nephropathy Once the diagnosis of BK virus nephropathy, suggesting that the transplanted kidney has caused damage, and the main cause of BK virus nephropathy is excessive immunosuppression, therefore, the first treatment principle for BK virus nephropathy is to adjust the immunosuppression. The first strategy generally used is to adjust the immunosuppressive dose downward, such as mycophenolate dose, and adjust the tacrolimus or cyclosporine dose if necessary. If dose adjustment is not effective, the next step is to switch the immunosuppressive regimen, such as switching from mycophenolate to leflunomide or to imipramine, but there is no uniform regimen and individualized treatment regimens can only be determined on an individual basis. Our current common regimen is tacrolimus + leflunomide + prednisone, to which some patients add regimen of ralston polysaccharide tablets. Some patients also take tacrolimus + low-dose mycophenolate + prednisone. Still other patients take tacrolimus + imipramine + leflunomide + prednisone. These regimens need to be adjusted according to the patient’s response after treatment. Timely switching of the immunosuppressive regimen, regular observation of the treatment effect and readjustment of the drugs is the key, as there is no uniform treatment regimen and one has to figure it out in the treatment. Some cases are more complicated and those with combined rejection are not suitable to change to leflunomide, and only mycophenolate dose can be adjusted downward. Some patients with combined tacrolimus or cyclosporine toxicity have to adjust the drug concentration downward to reduce transplant renal damage. Because BK virus nephropathy is caused by viral replication, some transplant centers also use antiviral drugs such as cidofovir for treatment, but due to its side effects, the effect is very little is not widely used, looking forward to the introduction of more effective antiviral drugs with fewer side effects. 5.What is the prognosis of BK virus nephropathy? Due to the lack of effective treatment for BK virus nephropathy, many patients do not have significant improvement in the transplanted kidney after treatment, and maintaining stable function of the transplanted kidney is successful. In some patients, the function of the transplanted kidney gradually deteriorates after diagnosis, eventually leading to transplant kidney failure. The average survival time of this group of patients is 2-3 years as reported internationally. In our transplant center, due to the use of special drugs and individualized treatment plan, the average survival time of the transplanted kidney is 3-5 years, and the longest one has been more than 6 years, and the blood creatinine is still stable. Therefore, even if you have BK virus nephropathy, don’t be overly pessimistic, as long as you can get timely treatment, it can be controlled for some time. In conclusion, BK virus nephropathy after kidney transplantation is an important factor causing transplantation kidney damage, which needs the attention of the transplant surgeon, and regular monitoring of BK virus replication after surgery is an effective measure for early detection and prevention of virus nephropathy. The diagnosis of BK virus nephropathy depends on biopsy of the transplanted kidney and special tests. Once the diagnosis of BK virus nephropathy is made, treatment requires timely adjustment of the dose and type of immunosuppressive agents, and individualized treatment is the key to successful treatment.