By translating viruses from RNA to DNA, scientist have developed effective vaccines — for fish. From Vaccines That Keep Salmon Safe to Eat May Help Humans:
The domesticated fish are Atlantic salmon, favored by farmers for their docile temperament and fast growth — qualities that make them the Hereford cattle of aquaculture. But unlike indigenous types, the transplanted species have little natural resistance to the local virus, which causes fatal hemorrhaging, and can contract it from the wild fish swimming past their pens.In mid-2001, a destructive epizootic, the animal equivalent of an epidemic, struck, sickening Atlantic salmon in 36 farms over a two-year period. In some pens, more than 90% of the young fish succumbed.
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The large loss of fish spurred new efforts to develop a vaccine against the virus, which causes the untreatable disease called Infectious Hematopoietic Necrosis, or IHN. This time, scientists tried arming the immune system using a snippet of viral genetic code translated into DNA, rather than a traditional approach, such as culturing a weakened IHN virus.
In detail:
Scientists at Aqua Health, a unit of Novartis in Prince Edward Island, Canada, solved the problems of potency and mass production. They took advantage of work by Ottawa scientists, who put a gene for a protein that covers the IHN virus in a ring of DNA, or plasmid, which some bacteria use to share genetic code. A single shot of vaccine behind the salmon’s dorsal fin contains 10 micrograms of these DNA rings.Plasmids make their way into muscle cells, much as infecting viruses do, where they spur the cells’ protein-making machinery to pump out copies of the viral protein. By tricking these cells to make telltale proteins of a virus, the DNA-based vaccines better mimic infections and so can confer greater protection.
Like salmon swimming upstream, the viral protein produced by the fish cells migrates into the bloodstream. The fish gird for battle by producing antibodies and preparing white blood cells to fight the virus, a response traditional vaccines barely stimulate. After a few months, the muscle cells containing the plasmids die — as normal muscle cells would — so fish vaccinated as youngsters carry virtually no traces of vaccine except their immunological armor.