What Is BK Viral Nephritis?

Medically Reviewed by Poonam Sachdev on October 18, 2022
5 min read

Over 20,000 Americans receive kidney transplants annually. After this procedure, some recipients develop a serious infection known as BK viral nephritis. This condition can affect your kidney function and reduce the likelihood of your transplant succeeding.  

Fortunately, there are several ways to prevent BK viral nephritis. Read on to learn about this infection’s causes, symptoms, and treatments.

BK viral nephritis is a dangerous infection that happens when the BK polyomavirus reactivates inside your body after a kidney transplant. BK virus was first discovered in 1971 in a kidney transplant patient with the initials “BK”. 

BK virus is a mild respiratory infection that spreads through secretions like mucus. BK virus symptoms are usually undetectable, especially in healthy people. You may not realize that you have contracted BK virus. Still, it can remain in your body as a latent, or dormant, infection. 

Over 80% of the general population has antibodies against BK virus, which means that many people have been exposed to it. Research on serology, or blood serum, suggests that most people contract BK virus during childhood. Individuals who don’t receive kidney transplants often carry the BK virus throughout their lives without ever getting sick.

If you receive a kidney transplant, you will typically take anti-rejection and immune suppression medications to increase the odds of your body accepting the new organ. These medications weaken your immune system and make it harder for your body to fight off infections. For instance, people who take immunosuppressants are more likely to get sick with infections like the flu, sepsis, and skin fungus. 

If you already have BK virus in your body, taking immunosuppressants after a kidney transplant can weaken your immune system so much that the virus reactivates. The virus attacks your kidneys and causes nephritis, or inflammation, in your ureters and other parts of your kidneys.

The ureters are thin tubes that connect the kidneys to the bladder, allowing urine to move between the two organs and exit your body. When these tubes swell up because of BK virus, you may experience problems urinating and other symptoms.

BK viral nephritis can lead to BK virus nephropathy, which means your kidneys stop functioning properly and may eventually fail. An estimated 2% of kidney recipients develop BK nephropathy.

People with BK viral nephritis often have no symptoms. People with symptomatic cases may notice these signs:

  • Bloody or reddish-brown urine
  • Discomfort or pain when urinating
  • Trouble urinating 
  • Feeling like you can't empty your bladder all the way
  • Sudden weight gain of two or more pounds that occurs within 48 hours
  • Tenderness or pain in your stomach or lower back

Urine tests and other lab work may detect abnormalities like increased blood urea nitrogen and higher creatinine levels.

If you experience any of these symptoms, you should consult your renal specialist. 

Most BK virus infections occur during the first three months following a kidney transplant, so you should be especially alert for signs of nephritis and nephropathy during this period.

BK viral nephritis can threaten the survival of your new kidney. An estimated 1% to 10% of transplant recipients develop this condition. BK virus reactivation causes graft loss in an estimated 30% to 80% of cases. 

Along with potentially hurting your new kidney, BK virus can injure your bladder. It may also spread to other body parts, including the brain, eyes, and lungs. You may develop other serious conditions as the virus spreads, including: 

  • Cancer. Cells may grow abnormally due to BK virus, causing malignant tumors to develop on your organs. 
  • Capillary leak syndrome. This serious condition occurs when plasma leaks out of tiny blood vessels into surrounding muscles, organs, and tissues.
  • Encephalitis. BK virus can cause inflammation in your brain tissue. This condition can cause symptoms like personality changes and seizures. 
  • Pneumonia. This infection causes fluid to fill your lungs, making it difficult for you to breathe.  
  • Viral hepatitis. If BK virus spreads to your liver, it can cause inflammation.

Your doctor may perform several tests to determine a BK virus diagnosis. Common tools used to diagnose this disease include: 

  • Blood test. Your doctor may draw a blood sample to detect the presence of viral DNA or mRNA associated with BK virus.
  • Kidney biopsy. A renal allograft is the most reliable way to diagnose BK viral nephritis. Your doctor will take two samples to improve the test’s accuracy.
  • Urine test. A urine test may detect decoy cells if you have BK viral nephritis. These cells come from infected cells in your kidney and pass into your urine. Like a blood test, a urine test may also show viral DNA or mRNA related to BK virus.

Few studies have examined the effectiveness of treatment strategies for BK viral nephritis, so there is no definitive treatment for this condition. However, your doctor can use several management strategies for BK virus treatment, including: 

  • Ordering antiviral medicines that may reduce your virus levels 
  • Prescribing medications that will boost your immune system to help it fight the BK virus
  • Switching you to a new anti-rejection medication 
  • Treating you with antibiotics if you have developed a secondary infection like pneumonia

Because most people contract BK virus during childhood, you can’t control if you have this latent virus. But there are several steps that you can take to reduce your chances of developing BK viral nephritis after your kidney transplant. Recommended preventative steps include:  

  • Using blood and urine tests to screen for BK viral nephritis before you develop symptoms 
  • Lowering your doses of immunosuppressive medications if your screening tests detect BK virus 
  • Having surveillance kidney biopsies to test for BK viral nephritis 

Experts recommend kidney recipients get screened for BK viral nephritis every three months for the first two years following the transplant surgery. After two years, screenings can continue annually until the fifth year. 

Keeping a close eye out for any symptoms of BK viral nephritis and following your doctor’s orders for preventative screening can help protect yourself from this serious infection. By reducing your chances of developing BK virus nephropathy, you can boost your chances of enjoying your new kidney for many years.