BK Virus DNA Quantitative

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1. What are Polyomaviruses infections?

These are viral infections. BK and JC virus cause exclusive infections in humans where as SV-40 primarily infects rhesus monkeys but can affect humans too. Primary infection with these viruses usually occurs during childhood which is largely asymptomatic, and may result in transient viruria (shedding of virus in urine). Serological evidence of this infection is seen in more than 50 to 70% people till adolescence. BK virus is also found in up to 3% of pregnant women but is not associated with any form of disease.

2. What is the mode of transmission?

This infection can spread via respiratory droplets, coming in contact with infected blood or body fluids (like saliva, urine or semen), after organ transplantation or from mother to child during delivery.

3. What are the diseases caused by BK virus?

BK virus infections are rare in immunocompetent adults and usually cause mild respiratory illness or, rarely, cystitis. In patients of kidney transplant, this virus can cause tubulo-interstitial nephritis (most common) and BK virus associated nephropathy (BKVAN) in upto 5% recipients. It takes on an average about 40 weeks from the time of transplant for these entities to occur. However, it can occur any time between 6 to 150 weeks. Most severe outcome is irreversible graft failure and kidney allograft rejection. Another dreadful entity is urinary bladder involvement - hemorrhagic cystitis which develops in patient who underwent hematopoietic stem cell transplantation.

4. What are the symptoms of this infection?

Virus is inactive in healthy immune individuals and does not show any signs or symptoms. When you become immune-compromised, virus becomes active and patient comes with symptoms like blurring of vision, reddish urine, pain and difficulty while passing urine, cold, cough, breathing difficulty, fever, weakness, muscle pain or at times fits (seizure).

5. What is the clinical relevance of this test?

Detection of BK virus DNA in blood or urine samples may support the clinical diagnosis of kidney or urinary tract system disease. This test helps use to monitor the progress of BKVAN in kidney transplant patients. Persistence of BKVAN correlates well with positive blood results for BK virus. New immunosuppressive therapy increases the risk of BKVAN and it is observed that the virus disappears from the blood after reducing immunosuppressive therapy.

6. Which PCR test should be done first – urine or blood?

Initially qualitative PCR testing of urine must be done to see for presence of BK virus. If present, then it is important to proceed with quantitative testing. Higher the viral load in blood, more likely is the presence of renal disease.

7.  What is the importance of PCR testing in this infection?

PCR is a rapid and highly sensitive test to detect and quantify BK virus DNA in plasma or urine. This is because; PCR detects the presence of infection at a genetic level by looking for the presence of DNA of the pathogen in the human body. This is a non-invasive modality for identifying patients at risk for BK virus related illness and also for monitoring response to therapy. In future times, role of PCR is likely to increase in the field of diagnostics due to its excellent sensitivity and specificity. Another added advantage is BK virus PCR test does not show cross reactivity with other polyomaviruses (JC and SV-40).

8. How frequently this test should be done in kidney transplant patients?

Monitoring for BK virus is recommended every three months for the first two years and then once yearly till 5^th year after renal transplantation or when kidney allograft dysfunction occurs. BKVAN is most frequently seen in initial 2 years after transplantation.

9.  Does PCR testing have any limitations?

PCR is a highly sensitive technique, but at times unexpected or paradoxical results can come. This can be due to contamination during sample collection, selecting inappropriate specimens or some kind of in-built or pre-existing PCR inhibitors in the specimen.

10.  Can this test be done for routine population screening?

No. This test cannot be done to screen healthy asymptomatic patients because variable percentage of people can have positive test results without having any risk factors or symptoms. During latency period, there should be absence of viremia (virus in blood), however low levels (<2,000 copies/mL plasma) are seen in some asymptomatic individuals.

11.  What are the other modalities for diagnosis of BK Virus infection?

A negative result does not rule out the possibility of BK virus infection. So other modalities for diagnosis include urine cytology examination and kidney biopsy. Presence of Decoy cells, a type of infected cell which suggests reactivation of latent virus, in urine cytology favors viral infection. It is not diagnostic but absence of decoy cells is usually suggestive of absence of viral nephropathy. Definitive diagnosis is made by studying kidney biopsy and documenting characteristic pathological changes. This can be further supplemented by doing immuno-histochemistry or electron microscopy examination on the biopsy specimen.

12.  Is this infection treatable?

Yes. If you have been diagnosed with this infection, you need to visit your nephrologist. They will modify the existing immunosuppressive therapy and try to eliminate the virus while preserving the kidney function and avoiding any short or long term kidney graft rejection.

13.  How can this infection be prevented?

Prevention is the most important key for all kinds of infection. BK virus infection can be prevented by regular screening in post transplant patients to detect viremia or viruria. When test results are positive, visit your nephrologist for timely treatment modifications and thereby prevent the infection.

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