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Monday, Mar 30, 2015

Medical sleuthing unmasks supposed hepatitis virus

Suncoast News staff report

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Never mind.

That, in a nutshell, was the word from medical detectives who investigated the discovery of what was thought to be a new strain of hepatitis virus.

Using cutting-edge genetic analysis, Charles Chiu and the team under his directorship at the University of California, San Francisco Viral Diagnostics and Discovery Center unmasked the supposed sixth hepatitis virus as merely genetic material from a tiny marine creature.

In June, researchers in the hematology branch of the U.S. National Heart, Lung and Blood Institutes reported they had used what is known as "deep" gene-sequencing to discover a "hybrid DNA virus" in serum specimens from 92 people in China who were suffering from cases of hepatitis that could not be attributed to any of the known hepatitis viruses, strains A, B, C, D or E.

The NHLBI scientists dubbed their discovery parvovirus-like hybrid virus, or PHV.

Working independently from the NHLBI researchers, Chiu and his team were able to detect the supposed PHV genetic fingerprint in serum samples from a different set of patients with hepatitis not associated with any of the five know viruses.

That, however, is not where the story ends.

"At first we thought this was a genuine hepatitis virus, but later we found it in data sets from patients with many other diseases and even from animals," said Chiu, a professor of laboratory medicine at UCSF.

The UCSF team made this discovery after they applied a series of what has been dubbed "next-generation" DNA sequencing analysis on the supposed PHV genetic material and then compared the results with known viral genetic material sequences found in database catalogs.

What they concluded was that PHV was actually a virus known to be present in diatoms that are found off the coast of California and Oregon and, as far as anyone knows, nowhere else on Earth.

Diatoms are tiny, often single-celled, algae that are chlorophyll-containing plankton. The cell walls of diatoms are made from silica.

Diatoms got into the act because researchers isolate the genetic material for sequencing by spinning serum samples at high speed in centrifuges. The samples are centrifuged inside small glass vessels known as spin columns.

"The silica used in nearly all commercial spin columns is derived from the cell walls of diatoms," Chiu said. "We believe that PHV may be a diatom virus that had inadvertently contaminated the silica-based spin columns during manufacture."

Next-generation sequencing has made such genetic analysis faster and cheaper, but its very power raises the risk of sample contamination of the sort apparently seen in the NHLBI research.

v vThis is not the first time Chiu and other UCSF researchers have uncovered mistaken discoveries related to viruses.

They previously discovered that a virus known as xenotropic murine leukemia virus-related virus discovered in 2006 in tissue from cancerous prostates was not in the tissue samples when they were taken. Actually the XMRV came from lab mice used in creating experimental tissue cell lines.

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