Hollow Spheres Make Solid Vaccine To Protect Fish

Emerging virus-caused diseases, a worldwide aquaculture problem, have caused a 24 percent decrease in salmon production in the United States alone over the past seven years, according to "Aquaculture Outlook," published by the Economic Research Service, U.S. Dept. of Agriculture. Infectious pancreatic necrosis virus (IPNV) causes high death rates of young hatchery-reared salmonoids. There is no reliable commercial vaccine available for IPNV, the researchers reported.

Scientists of UMBI's Center for Biosystems Research in College Park, MD, and collaborators developed the new vaccine through recombinant DNA technology. CBR virologist Vikram N. Vakharia said that he and colleague Raghunath B. Shivappa used an insect virus in cabbage looper caterpillars to produce quantities of IPNV-like particles. The virus-like particles are hollow shells, the complete protein coat of the virus.

In experiments at aquaculture facilities in Norway and West Virginia, the vaccine composed of such particles caused the immune system to produce antibodies in test fish, demonstrating a resistance potential against the viral disease. Vakharia said the technology promises to usher in new generation of recombinant vaccines for fish.

The ultimate goal of the UMBI work, said Vakharia, is to offer aquaculture operations an immersion vaccine technology. They would simply bathe thousands of fish fry in tanks of water laden with high doses of the vaccine. The new vaccine is harmless to the fish.

In the first of two types of experiments, scientists at the Norwegian School of Veterinary Science injected a single dose of the UMBI vaccine into adult Atlantic salmon. The vaccine evoked a protective response after the fish were exposed to the disease virus. Vakharia said 65 percent of fish injected with the experimental vaccine survived the disease exposure compared with a survival rate of only 23 percent for control fish that were not vaccinated.

In West Virginia, Shivappa found that 43 percent of rainbow trout fry, which had been immersed for five hours in holding tanks with the vaccine, were cross-protected against a heterologous virus challenge. He conducted the experiments at the U.S. Geological Survey's National Fish Health Research Laboratory in Kearneysville.

Vakharia told the symposium, "these results are good, but we still have not optimized the dose of the vaccine." Vakharia's team cloned genes of the virus that produce the proteins, which make up its outer, spherical coat. The virus-like particles are thus hollow spheres that resemble the scaffolding of the virus but it cannot reproduce and cause disease.

With strong growth in recent years, salmon aquaculture has surfaced as a $4.9 billion dollar industry that produces 1.6 million metric tons of fish globally, reported in the Review of the State of World Aquaculture, Fisheries, 2003, U.N. Food and Agriculture Organization. But viral diseases can devastate a commercial operation. Norway, for example, the world leader in salmon production, reports an annual loss to IPNV disease in excess of $60 million.

UMBI has filed a patent application for the IPNV vaccine that will soon be available for licensing. For information on licensing technology, please contact Rita Khanna, Director of Technology Transfer at khannar@umbi.umd.edu or 410-385-6324.

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The University of Maryland Biotechnology Institute was mandated by the state of Maryland legislature in 1985 as "a new paradigm of state economic development in biotech-related sciences." With five major research and education centers across Maryland, UMBI is dedicated to advancing the frontiers of biotechnology. The centers are the Center for Advanced Research in Biotechnology in Rockville; Center for Biosystems Research in College Park; and Center of Marine Biotechnology, Medical Biotechnology Center, and the Institute of Human Virology, all in Baltimore.