Fishing for a Cure

Two marine biologists at the University of Hawaii are developing a fish vaccine to prevent a widespread and often fatal parasitic problem

January, 2004

Jo-Ann Leong and Teresa Lewis want to make sure Hawaii doesn’t get the tropical “ich.” Though the letter “t” is missing, the meaning is the same – except ich is an itch that fish get from parasites. Leong and Lewis, who are marine biology researchers at the Hawaii Institute of Marine Biology (HIMB) on Coconut Island in Kaneohe Bay, have initiated a program funded by the U.S. Department of Agriculture, the National Oceanic and Atmospheric Administration and the federally funded Hawaii SeaGrant program to study this warm-water scourge. Leong’s fish virology research has brought in about $850,000 over the past few years.

The cryptocaryon parasite burrows into the mucous membranes of warm-water fish and irritates their skin. The parasite causes white lesions. Itchy fish rub themselves on rough or hard surfaces to try to alleviate the irritation and often rip off chunks of their skin. In many victims the parasite leads to other health problems and eventually to death. “They itch, get real sick and many of them die,” says Leong, who is the director of the HIMB, a unit of the University of Hawaii’s School of Ocean, Earth Science and Technology (SOEST).

Just as they do in the rest of the tropics, cryptocaryon infect many Hawaii fish varieties, including opakapaka, kahala and various snappers and reef fish. That’s a big problem as the state seeks to grow its aquaculture industry. In 2002, according to the USDA, Hawaii aquaculture products had a gross value of $25 million. Fish are one of the fastest growing aquacultural products. Since 1998, the value of finfish grown in Hawaii has increased 180 percent, from $958,000 to $2.638 million. The Hawaii state Department of Agriculture hopes to grow that segment to $5 million by the latter half of this decade. With the success of the moi farms off the Waianae Coast and promising developments in other finfish aquaculture operations on the Kona Coast and at the Oceanic Institute near Makapuu, that goal appears increasingly realistic.

To meet it, though, the fish farmers may need Leong and Lewis to help them fight fish diseases that spread like wildfire among confined populations typical in aquaculture operations. Both Leong and Lewis are world-class experts in fish diseases, with broad experience in how the immune systems of fish function. Their plan? First they want to sequence the genome of cryptocaryon and get a clearer picture of how the parasite infects and affects fish. Then they hope to develop a fish vaccine that aquaculturists could easily administer to their fish either through simple injections or skin-absorption techniques.

Such vaccines might sound exotic, but are actually fairly commonplace. Leong developed two fish vaccines while working at Oregon State University in the 1970s and 1980s, which were among the first in the field. Those vaccines immunized salmon and rainbow trout against two different types of fatal viruses that had plagued the fish-rich rivers of that rainy state, as well as its fish farms. Those farms represent businesses worth hundreds of millions of dollars in the Pacific Northwest. One of Leong’s vaccines, which guards against a virus that damages fish livers, is widely used by fish farmers in Norway.

Today, companies manufacture 10 different vaccines protecting dozens of farmed species. Many fish farms have been able to dramatically cut their use of antibiotics by immunizing their fish.

However, Leong and Lewis face some obstacles. Decoding the genome of a single-celled parasite is actually far more complicated than decoding the genome of a virus. “A virus genome only carries 12 kilobytes of information. A parasite genome will carry megabytes of information,” explains Leong, who expects the effort to take more than a year. Further, while the white spots and subsequent health problems in fish caused by cryptocaryon are well documented, scientists understand very little about the life cycle and habits of cryptocaryon. This information, says Leong, will be necessary in building a vaccine.

However, Leong and Lewis hope to copy the basic vaccine-building methodology that Leong used in the two salmon-virus vaccines. This will entail isolating the cryptocaryon gene that encodes a surface protein of the parasite and then, placing that gene into a DNA vector that would be easily absorbed by or injected into fish. By doing so they actually program a strong defensive response to the parasite into the fish’s immune-response system. To ensure that the added gene does not disrupt the fish’s own genome, Leong and Lewis can build a self-destruct function into the vaccine, which ensures that the injected genes do not persist. “It’s only one gene, so it’s very safe. And it’s extremely effective,” says Leong.

A cryptocaryon vaccine could also prove lucrative. Leong and Lewis hope to patent the technology so the UH will have the option of licensing the vaccine to a commercial entity for widespread production and use around the world. What’s more, these types of fish vaccines could become increasingly important in maintaining aquatic populations. Says Leong, “There are disease outbreaks in wild fish quite frequently. Our fisheries are beginning to decrease. So we are going to have to practice conservation biology to bring some of these fish back to healthy levels. And we are going to have to understand how to rear them without disease.”

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Alex Salkever