What is BK Virus?
BK virus was first identified in the urine of a renal transplant patient in 1971 with the initials B.K. It is similar to another virus called JC virus and is a member of the polyoma family. You may also hear it referred to as polyomavirus.
The incidence of BK virus has increased over recent years however this may be, in part, that we are now screening for it more often. However modern anti-rejection drugs, though better at preventing rejection, may have increased the risk from some virus infections.
BK virus is reported in several studies to occur in around 3% (3 in every 100) of the renal transplant population and usually occurs within the first year following transplantation.
How does BK virus spread?
Exact transmission of the virus is unknown but it is known that spread occurs from person to person and not via animals.
It is thought that most people have a latent (sleeping) form of BK virus which does not cause trouble until they are immunosuppressed by the anti-rejection drugs used in transplantation.
How will I know if I have BK virus?
Most people who have BK virus will have no symptoms.
BK virus can be, and usually is, acquired without you knowing about it. When people are on immunosupressant drugs for a transplant they are at increased risk of acquiring BK virus and it causing a problem.
There are several ways of checking for BK virus and depending on which hospital you attend will depend on which test are carried out.
BK virus can be checked for in urine, blood or by staining on a kidney biopsy. Some terms which you may hear used are:
- Viruria detection of virus in the urine (often not associated with any change in kidney function)
- Viraemia detection of virus in the blood (often not associated with any change in kidney function)
- BK Nephropathy detection of virus in a kidney biopsy
What is BK nephropathy?
Sometimes found in biopsies done because of a deterioration in kidney function. Usually there are signs of inflammation and damage to the kidney from the infection. Although it is sometimes obvious that it is caused by a virus, at other times the virus can only be seen using special methods.
How can it be treated?
The usual treatment of BK viraemia or nephropathy is reduction of immunosupressant drugs. This usually begins with either MMF or azathioprine. We sometimes try other methods, but there is not convincing evidence for any particular one. It is difficult because as you reduce immunosuppressants there is always the possibility that rejection will occur. You will probably need more frequent checks and maybe drug and dose changes. You might need a follow-up biopsies.
How does BK virus affect my transplant?
There is a spectrum of severity – sometimes mild, and gets better, but sometimes severe. BK nephropathy is difficult to treat and can cause lasting damage.
Is there anything new coming along?
The best things would be a new anti-virus drug that isn’t too toxic. Until there is one, prevention is best, so balancing the amount of immunosuppression with the risk of infection is key.