Lab-grown parasite offers hope for oyster disease

April 30, 1993|By Liz Bowie | Liz Bowie,Staff Writer

Scientists say a seemingly minor laboratory breakthrough has raised new hopes that science might yet find a cure for one of the diseases that is lethal to the oyster -- that beloved bivalve so integral to the health of the Chesapeake Bay.

For 40 years, scientists couldn't find a way to grow the disease-causing Dermo parasite in their laboratories.

Without that ability, the chance for further scientific understanding of the disease was blocked. Researchers were left watching Dermo and a second disease, MSX, spread up the Chesapeake Bay, destroying vast areas that had once supported a large industry.

Now, just as predictions for oyster harvests look more bleak than ever, researchers at the Center of Marine Biotechnology (COMB) in Baltimore say they now dare to imagine a drug that could cure Dermo or a genetically engineered oyster resistant to it.

"This opens a number of doors in the understanding of the disease," said Gerardo Vasta, an associate professor at COMB. "I think there is hope for the Eastern oyster."

Dr. Vasta is one of three researchers working independently to develop a culture that allows Dermo to grow in the laboratory. Two other scientists -- one at the Virginia Institute of Marine Science at Gloucester Point and a second at Rutgers University's laboratory in Bivalve, N.J. -- also say they made the discovery this year.

All three scientists say their results will be published within the next month.

Now that marine scientists can grow Dermo in the lab, they can work to understand why the oyster's immune system does not attack the parasite. With further research, they hope to engineer a cure and perhaps find a gene that can be inserted into an oyster to make it resistant to the disease.

"The new tools of biotechnology offer the best -- and maybe the only -- hope for dealing with oyster disease," said Chris D'Elia, a longtime bay researcher and director of the Maryland Sea Grant College, which helped pay for Dr. Vasta's research.

A cure to Dermo is believed to be years away and by no means assured, scientists caution. And even if scientists can manipulate the oysters' immune system, major obstacles remain before the population can be brought back to healthy levels in the Chesapeake.

For example, MSX disease has proved even more confounding to scientists than Dermo and just as deadly to oysters. MSX and Dermo have no effect on people who eat the oysters.

Also, some biologists have also argued for years that overfishing and pollution have been as detrimental to the oyster as the diseases.

Another question is whether a genetically engineered version of the wild Eastern oyster should be released into the Chesapeake. And if an effective drug is found, would it be safe to place into the water above oyster beds?

The Chesapeake oyster is not just a delicacy that has been slurped down for centuries across the nation. When abundant, the oysters also act as large water-filtering devices, sucking out pollutants in the bay. Once the bay's oyster population, which survived in vast reefs just under the surface of the water, filtered the entire Chesapeake in just five days. Now it takes about a year.

So a healthy oyster population is seen as a key to helping restore the bay.

The breakthrough in culturing Dermo apparently came recently because the medium, or chemicals, needed to grow the parasite are much more advanced today.

In addition, the disease-producing parasite is more widely known.

"I am sure others had it in the culture, but they didn't know what it was," said Jerome F. La Peyre of VIMS.

Both he and Stephen J. Kleinschuster, a professor of marine coastal sciences at Rutgers, say they accidentally stumbled across the parasite in petri dishes or test tubes.

Dr. D'Elia said increased competition among scientists in the field also has helped to improve the pace of discovery.

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