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NMSU biologist studies effectiveness of virus-removal filters

Oshima is researching the capabilities of filters made of polyvinylidene fluoride (PVDF) membranes, using a variety of fluids contaminated with different viruses -- including the hepatitis B and hepatitis C viruses that can cause serious liver disease. He has found that the filters provide an efficient method of removing viruses and that performance is tied predictably to the size of the virus in question.

New Mexico State University biologist Kevin Oshima at the biological safety cabinet he uses in evaluating new virus-removing filters. (NMSU photo by Michael Kiernan)

"The bigger the virus, the better the removal," he said. "Larger viruses can be removed to below detectible levels" using filtration.

Complete elimination of viruses "is something we can't measure," he noted, so usually more than one method is used to validate the safety of a vaccine or other biological product. "You can couple filtration with heat, irradiation or detergents, for instance."

Oshima will present the findings of his research on virus filtration at a Viral Clearance and Testing symposium in San Diego Feb. 15. The symposium is part of a two-day Process Validation for Biologicals conference for the pharmaceutical industry.

An environmental biologist whose main research focus is viral contamination of water, Oshima began his work with virus filters while he was a post-doctoral researcher at the federal Centers for Disease Control (CDC) in Atlanta, before joining NMSU in 1996.

The PVDF membrane filters he tests in his NMSU laboratory are far removed from the coffee filters and oil filters most of us are familiar with. Viruses are smaller than the average cell -- too small to be seen with anything less than an electron microscope. A filter that can trap viruses must be extremely fine and uniform.

"The technology is getting better," Oshima said. "You have to be able not only to make the filters that tight, but also make them reproducible" so that the results are predictable.

Oshima has examined the virus-removing capabilities of PVDF membrane filters manufactured by Pall Corp. of East Hills, N.Y., which provides the filters for testing. Newer, tighter filters have proven to be more efficient at removing smaller viruses than previous versions, he said. But there is a downside to ever-tighter virus filters, Oshima noted: At some point "you have to worry about what they remove that you want to keep" in the vaccines or other products.

Although all viruses are vanishingly small, some types are larger than others. Influenza viruses, for instance, are two to three times bigger in diameter than the hepatitis viruses that Oshima has been working with most recently. The challenge in virus filtration is to remove the smallest viruses possible without removing the therapeutic components of the fluid.

The findings Oshima will report at the San Diego conference are from a collaborative study with Pall Corp. Other findings on the use of the filters are being presented at the conference by scientists from the CDC and from Protein Design Labs Inc.

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PHOTO: kevin_oshima.jpg
CUTLINE: New Mexico State University biologist Kevin Oshima at the biological safety cabinet he uses in evaluating new virus-removing filters. (NMSU photo by Michael Kiernan)

Karl Hill
Feb. 9, 2000