BK virus (Hemorrhagic cystitis)

Definitions & Key takeaways

The BK virus is a double-stranded DNA virus that infects the kidney epithelial cells, causing life-threatening hemorrhagic cystitis in immunocompromised people, especially in bone marrow transplant recipients. It can also cause nephropathy and ureteral stenosis in kidney transplant recipients. Symptoms include suprapubic pain, hematuria, symptoms of chronic kidney disease such as edema; fatigue, and breathlessness due to anemia.

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Introduction 0:00–0:46

BK virus or BKV is named after the initials of the patient in whom the virus was first identified BK virus typically infects the urinary system of immunocompromised individuals or those with a weakened immune system, especially those receiving immunosuppressive medications following organ transplants.
Major clinical manifestations of BKV infection include hemorrhagic cystitis, which is inflammation of the urinary bladder associated with bloody urine in bone marrow transplant recipients, ureteral stenosis or narrowing and nephropathy in kidney transplant recipients.
BK virus belongs to the polyomavirus family. Along with the JC virus, these contain a circular double stranded DNA genome which is surrounded by an acoss capsid which is a spherical protein.

Viral characteristics 0:46–1:09

She made up of 20 equilateral triangular faces. They are also called non enveloped viruses.
Since the capsid isn't covered by a lipid membrane. Now, it turns out that the vast majority of the population is infected with BK virus during their childhood.

Transmission 1:09–1:26

The virus is thought to be transmitted from person to person through respiratory droplets when someone coughs or sneezes and by ingesting contaminated food and water.
Once inside the virus moves through the bloodstream and eventually reaches the kidneys. Specifically the renal tubular epithelial cells where it starts to replicate.

Pathophysiology 1:26–4:31

But the cytotoxic CD eight positive T cells in our immune system, keep the virus in check by killing any cell that has replicated BK virus inside it.
However, the sneaky little viruses are not eliminated, but instead they hit the snooze button and go into a latent phase within the kidney epithelial cells.
In other words, they're not dividing or causing disease. Most people with a healthy immune system are able to keep BK virus in the latent phase in the kidney epithelial cells for their entire life.
But things can change if the immune system gets weaker. This can happen for various reasons like in HIV, infected individual who loses T cells or individuals taking immunosuppressive medications like tacrolimus.
Tacrolimus is a medication primarily used to reduce the immune response after organ transplantation to prevent transplant rejection.
BK virus infection is especially common in kidney and bone marrow transplant recipients. In immunocompromised individuals, T cells are affected and without them, the BK virus in the epithelial cells starts multiplying once again, which results in tubular cell death by lysis or the breakdown of the cell membrane, releasing the virus into the interstitial tissue.
This elicits an inflammatory response from the host, namely white blood cells like macrophages found in the affected tissue release, inflammatory mediators like histamine and cytokines.
This makes blood vessels in the infected area, dilate and become more permeable, allowing more leukocytes and fluid to enter local tissue.
The end results are the four cardinal signs of inflammation, heat, pain, redness and swelling. Now, because of vasodilation virus, in the interstitium can slide into the capillaries, lining the tubules and travel through the blood to reach different parts of the urinary system.
If the virus enters the ureteral epithelial cells, it causes inflammation which over time results in fibrosis and narrowing of the ureter walls called ureteral stenosis.
If the ureters are completely blocked, it results in hydronephrosis, which is the distention of the renal calices and pelvis with urine.
If the virus spreads to the urinary bladder, it causes inflammation and bleeding of the mucosa which is called hemorrhagic cystitis.
All this blood can form clots within the bladder which come to lie over the urethral opening and obstruct the flow of urine.
This leads to urinary retention. BK virus often spreads to newly transplanted kidneys and causes interstitial and tubular damage.
As a result, the kidney stops functioning, which is called nephropathy. Sometimes damage to the kidney is so severe that it can even result in transplant rejection.
Primary infection with BK virus is usually asymptomatic or produces mild common cold like symptoms that people can recover from on their own.

Clinical manifestations 4:31–5:12

Hemorrhagic cystitis usually presents with painful hematuria or bloody urine, increased frequency of urination, inability to pass urine due to obstruction by clots and lower abdominal pain.
Ureteral stenosis commonly presents with decreased urination and pain in the flanks BK virus. Nephropathy.
Symptoms are similar to those of chronic kidney disease, which include increased nocturnal or nighttime urination, edema, fatigue and breathlessness due to anemia.
Early detection of BK virus infection can help treat the disease in the early stage for this purpose. Regular screening is done in transplant recipients with the help of polymerase chain reaction or PCR assays that look for viral DNA in blood and urine urine can also be tested for decoy cells.

Diagnosis 5:12–5:48

These are virally infected epithelial cells that resemble renal cancer cells and can often mislead the diagnosis. The gold standard test for diagnosing BKV.
Nephropathy is immunohistochemical analysis of kidney biopsy specimens to look for viral antigens. The main goal of treatment is to reduce the immunosuppression, either by reducing the dose of immunosuppressant used or by switching to a less potent medication in HIV infected individuals.

Treatment 5:48–6:45

Antiretroviral medication like lamiVUDine, zidovudine and efavirenz are used to prevent viral multiplication and improve T cell count.
Leflunomide, which is an immunosuppressive medication with some antiviral properties can be used in the case of BKV nephropathy.
Treatment of hemorrhagic cystitis involves providing adequate hydration clot evacuation by placing a catheter into the urethra and flushing the bladder with water or sodium chloride solution to break up the clot care must be taken to avoid over distending.
The bladder, ureteral stenosis can be treated with a balloon dilatation where a deflated balloon is inserted into the stenosis.
Then it's inflated to open up the ureter or by placing a stent. All right, as a quick recap BK virus is a DNA virus that infects the kidney epithelial cells and sets up latent infection in individuals with healthy immune systems.

Review 6:45–7:24

It gets reactivated when the immunity lowers causing hemorrhagic cystitis. In bone marrow transplant recipients and nephropathy and ureteral stenosis in kidney transplant recipients.
Primary infection with BK virus is usually asymptomatic and symptoms during reactivation depend on which part of the urinary system is affected.
Diagnosis involves PCR assay, urine analysis and kidney biopsy. And treatment is aimed at reducing the immunosuppression.