A fine kettle of fish

2019-03-07 01:14:01

By Tim Thwaites in Sydney NORTH American salmon and trout producers are keen to begin using a new antiviral vaccine. But because the vaccination involves injecting DNA into fish, there are fears that fish treated in this way will provoke more food scares in Europe and Japan. The new vaccine provides nearly total protection against infectious haematopoietic necrosis virus, a major problem in North America fish farms. Outbreaks of IHNV can kill most of the fish in farms, costing the industry tens of millions of dollars a year. The vaccine was developed by government laboratories in the US and Canada, along with Clear Springs Foods, the world’s largest producer of trout. At the International Congress of Virology in Sydney earlier this month, researchers reported that when trout fry and smolt salmon were injected with as little as a millionth of a gram of the vaccine, no fish died when exposed to the virus, whereas 90 per cent of the controls perished. The protection has lasted more than three months so far. “The industry really wants this vaccine,” said Gael Kurath of the Western Fisheries Research Center in Seattle, who was one of the leaders of the research. But Curt Endresen, a fisheries expert at the University of Bergen in Norway, doubts if such a vaccine would be acceptable in Europe. “You are adding something to the fish, and that would not be popular.” The problem stems from the way DNA vaccines work. Unlike most vaccines, which contain material that triggers an immune response directly, what’s injected is DNA containing the gene for one of the viral proteins. This DNA is taken up by cells, which then begin to produce the viral protein, priming the immune system to attack the virus itself. A similar technique has already been used to develop human vaccines against the Ebola virus, HIV and other viral diseases. Although several of these vaccines are undergoing trials, none has yet been approved by the US Food and Drug Administration. Kurath says she and her team will wait for this approval before registering their fish vaccine. “Once the idea of human DNA vaccines is accepted, it will be easier for veterinary vaccines.” The vaccines do not genetically modify organisms. Kurath says there was no evidence that the introduced DNA was permanently incorporated into fish chromosomes. “It’s a theoretical possibility,” says Harriet Robinson of Emory University in Atlanta, a pioneer of DNA vaccines. But she says that the chances are tiny, and that even if the DNA did become incorporated into fish chromosomes, it should not cause problems. Nevertheless, consumers in Europe and Japan may regard the process as genetic modification, says Endresen. This perception might be made worse because the DNA comes from a virus. “We know too little about what happens to the viral material after we eat the salmon,” says Endresen. “Norway sells salmon to the rest of Europe and the Japanese. No one likes the idea.” Stephen Hunt, who studies risk perception at the Institute of Food Research in Norwich, agrees that fish which have received the vaccine could well get a bad press in Europe. “Anything that might be interpreted as genetic modification is likely to be interpreted in that way,” he says. However, Kurath argues that viral DNA is probably already in the salmon and trout that people eat. Her group has also been working with a Danish laboratory that has produced a DNA vaccine for the most important viral disease of trout in Europe,