Researchers Nearing Commercially Viable Cure to Abalone Disease Findings Also Assist in Conservation of Endangered Species

June 6, 2006

Contact: Christina S. Johnson, csjohnson@ucsd.edu, 858-822-5334

SEATTLE – In research that may benefit abalone aquaculture and endangered species recovery efforts, an experiment is underway to test whether a single dose of a common oral antibiotic might be a commercially viable cure for an abalone wasting disease that has decimated both farmed and wild abalones.

In preliminary experiments funded by NOAA’s California Sea Grant and led by professor Carolyn Friedman of the School of Aquatic and Fishery Sciences at the University of Washington in Seattle, one dose of the antibiotic oxytetracycline, used extensively in livestock, was shown to be 90 percent effective at curing withering syndrome.

Caption: Professor Carolyn Friedman is developing a cure for the abalone disease known as withering syndrome. Photos courtesy of University of Washington, Seattle.

George Trevelyan, director of research and development at The Abalone Farm in San Luis Obispo County and a collaborator on the Sea Grant project called the results promising. “Ninety-percent is pretty good for a farm situation,” he said. “We are excited about the results.”

Withering syndrome is a highly contagious bacterial infection caused by a rickettsia-like pathogen. (Rocky Mountain spotted fever and typhus fever are caused by rickettsial bacteria.) The withering syndrome bacterium is shed in abalone feces and is believed to enter animals while they feed.

In abalone with full-blown withering syndrome, the most obvious symptom of distress is severe atrophy of the foot muscle, the mollusk’s primary edible portion. A wild abalone uses its foot to adhere to substrate and locomote, like a giant snail. A diseased animal can do neither effectively and likely will die.

As with other microbial diseases, abalones can carry the disease-causing pathogen without showing any symptoms of infection. Warmer ocean temperatures, however, accelerate the pathogen’s transmission, causing a precipitous rise in incidences of full-blown withering syndrome in previously asymptomatic animals.

An abalone suffering from withering syndrome (Left). A healthy abalone (Right). Credit: J. Moore, California Department of Fish and Game.

The interest in developing a single-dose cure for the disease stems from earlier research, led by Friedman and colleagues at the University of California at Davis and the California Department of Fish and Game. In this work, also funded by Sea Grant, researchers established that oxytetracycline not only treats symptoms it also cures the disease itself. After a month of receiving either 20- or 30-day oxytetracycline treatments, all previously infected abalones tested negative for the presence of the withering syndrome bacterium. A 10-day treatment was 97 percent effective.

Based on these findings, The Abalone Farm bought an industrial Italian pasta maker, capable of churning out 200 pounds of noodles an hour. The farm uses the machine to make a kelp pasta, a proprietary mixture of various meals, including ground kelp, and a small amount of antibiotic. Dried noodles are fed to abalones as needed and under oversight from the FDA’s investigational new animal drug program, the regulatory process through which a drug’s safety and pharmacological activity are established.

Despite the promising results so far, there remains a significant hurdle to the full-scale commercial use of oxytetracycline as a treatment for withering syndrome. Because of a quirk in abalone physiology, abalones preferentially accumulate oxytetracycline in their digestive gland. (Why is a topic for future research.) As a result, it takes an inordinately long time for antibiotic levels to fall below the FDA’s human health standard, said Eric Rosenblum, a former doctoral student with Ron Tjeerdema at UC Davis, who led some of the abalone experiments.

Following a 20-day treatment, it takes about 9 months for antibiotic levels to drop below the FDA standard, Friedman said. For abalones approaching harvest, this translates into nine months of extra culture time – a significant increase in the cost of rearing an animal that otherwise would reach market size in 3 to 4 years. Even the single-dose treatment they have been experimenting with recently requires a 3- to 4-month clearing time.

The experiments now underway are focusing on finding the lowest effective single dose.

“Before we were asking how much OTC (oxytetracycline) for how long to get rid of withering syndrome,” Friedman said. “Now we are looking to find the dose that results in a certain level of OTC in the digestive gland that allows an abalone to purge itself of the pathogen.”

Credit: The Abalone Farm, Cayucos, California

A commercially viable cure for withering syndrome would be a huge boon for abalone farms along the rugged Central California coast between Santa Barbara and San Mateo. The 1997-98 El Nino was the nightmare example of the region's vulnerability to oceanic warming. That year, an outbreak of the disease resulted in the loss of about $1.5-million worth of product at two of the state’s largest farms, one being The Abalone Farm. “We saw our largest, most valuable abalone wither away,” Trevelyan said. “A single-dose treatment would be pretty major for us.”

Not just cultured but also wild abalones are vulnerable to disease, particularly black abalones. Populations of this intertidal species were reduced by more than 90 percent in some areas in the 80s and 90s. Biologists at NOAA Fisheries are now evaluating whether the black abalone should be granted protection under the Endangered Species Act. If so, it would be the second abalone species with federal endangered species protection, the other being the deep-water white abalone, the first marine invertebrate on the endangered list.

Despite their precarious status today, black and white abalones were once abundant and targets of lucrative fisheries. The Abalone Farm and other culture facilities raise red abalone, the largest of California’s seven native species, also once a wild-capture commercial fishery.

Given the connection between warming and disease, worrying about withering syndrome has become a summertime ritual for Central California abalone growers. (Growers in Northern California worry less about disease since their coastal waters generally remain cold year round.) “Whenever we see the water temperatures in our tanks hit 18 degrees (Celsius), we are concerned about an outbreak,” Trevelyan said.

Currently, prevention is the farm’s main strategy for managing – not curing – disease. “We keep seawater flowing fast through the tanks,” Trevelyan said. Ideally, the water should be cooler than 16 degrees. Antibiotics are a last option, he said, but a good one when needed. “The fact that we can now give them medicine and they will get better is really exciting.”

Recent experiments suggest it takes a month after medication ends for abalones to rid themselves of the disease-causing bacterium. This month-long period is independent of the duration of antibiotic treatment and reflects the mechanism by which the antibiotic halts disease. “OTC does not kill bacteria,” Friedman explained. “It halts their replication.”

“We have to give the animals time to purge themselves of the bacterium,” she added.

"The fact that we can now give them medicine and they will get better is really exciting." – George Trevelyan, director of research and development at The Abalone Farm.

The use of antibiotics is usually relegated to cultured animals, not as a tool for assisting wild populations. The situation for California’s wild white abalone, however, is so dire that what is being learned during the recent research is being applied to conservation efforts.

James Moore, a senior fish pathologist at the California Department of Fish and Game and a co-investigator on ongoing and recent California Sea Grant projects, said that the recovery plan for white abalone includes a captive-rearing program in which progeny from wild-caught broodstock are outplanted in the wild.

That abalones accumulate oxytetracycline in their digestive gland may have benefits for wild conservation, Moore said. The withering syndrome bacterium attacks digestive tissues. The antibiotic is thus retained precisely where its activity is needed most. An accumulation of antibiotic may extend protection from the disease for some months.

Tom McCormick, who is leading NOAA Fisheries’ white abalone captive rearing program and is a co-investigator on another Sea Grant abalone project, is now examining the efficacy of oxytetracycline in controlling mortality of white abalone. The Abalone Farm has donated some of its medicinal noodles that in the controlled environment of a laboratory are being fed to captive-reared specimens.

“Withering syndrome is endemic to all of Southern California,” Moore said. “But the few brood stock we collected were from very deep waters and were found to be free of the withering syndrome agent. We don’t want to outplant infected animals.” Feeding abalones optimal doses of antibiotic, before they are released in the wild, may help in this effort, he said.