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Researching Diseases in Wild Oysters


While farmed oysters are big business in Virginia, the Chesapeake Bay wild oyster is still struggling with bay pollution and two diseases, harmless to humans, but fatal to oysters.

Since the late 1980s, the Virginia Institute of Marine Science has conducted annual surveys to check on how wild oysters are coping.

Dermo also called perkinsus was the first to attack oysters in 1949 robbing them of nutrients and eating them from the inside out. Ten years later, MSX arrived from Asia. By the mid-1980s oysters were in big trouble with commercial harvests at historic lows. Now, that's slowly changing.

Ryan Carnegie, an associate professor at VIMS, is trying to figure how oysters are living longer even though disease levels remain high.

“On the wild beds the oysters are doing better and better and better, despite the fact that perkinsis remains at a historical high. We're asking why that is, what the oysters are doing right. Are they experiencing the same physiological consequences that they did in the past.”

While all Virginia wild oysters are infected with perkinsus, the latest surveys show a very low number are infected with MSX. And VIMS researchers found something very interesting - MSX may not even be an oyster parasite at all.

“Perkinsus is an oyster parasite. But if we sat MSX down and asked it who it really is, MSX would probably say to us, “well alright to be honest, I'm actually not an oyster parasite. I infect oysters and I can kill them but I prefer to infect something else.”

Carnegie says researchers have also learned more about perkinsus. It needs large populations of oysters to survive. Back in the 80's when the oysters were barely hanging on because of the two diseases, perkinsus morphed into a more lethal parasite, shrinking in size, growing in number and infecting a different part of the oyster.

“So the suggestion is, that this is actually change in parasite virulence where an older form, that was the only form that existed up until the 1980s, was replaced by a hyper-virulent form, like superbug of the parasite basically, that completely took over in the 1980s when disease intensified and it's basically now all we see.”

So will perkinsus ever die off? Carnegie says no. It's likely the parasite will continue to adapt. Meantime, MSX may be off enjoying something other than oysters.

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