PEI scientists: Current salmon vaccines aren’t working, but a cure may come soon

A team of Prince Edward Island scientists says that vaccines currently used to fight Infectious Salmon Anemia (ISA) may actually make the virus worse; that’s the bad news. The good news is that the same team at Atlantic Veterinary College, part of the University of Prince Edward Island, believes that it may be on the track of a real solution to the problem that has been plaguing Maine and Maritime salmon farmers.

Although the technicalities of the research are complicated, they all boil down to the following points.

There are “good antibodies,” and there are “bad antibodies,” according to Dr. Fred Kibenge, Professor of Virology at AVC. The antibodies now being used in vaccines are “virus-friendly antibodies” or “harmful antibodies,” he says. “What this indicates or suggests to us is that some virus proteins or antigens on the ISAV particles induce the production of these harmful antibodies. These antigens must be identified and excluded from ISAV vaccines in order for these vaccines to have substantial preventative value.”

Most importantly, Dr. Kibenge says, “We are getting close to the point of identifying these harmful antigens.”

The professor explains, “As you know, when a virus infects an animal host, the animal reacts by producing antibodies to the virus. Some of these antibodies bind to the virus and alert the immune system cells to come and destroy it. These are the good antibodies. That is how the animal fights off the infection, and that is why vaccination works to protect against infection and disease.”

He continues, “What we have discovered [for the first time with a fish virus] is that in case of ISAV, some of the antibodies produced against it in rabbits (and fish) actually help the virus to infect fish macrophage cells in culture. Thus when the cultured cells are exposed to serum containing the antibodies to ISAV and then ISAV is added, instead of the antibodies knocking out the virus and protecting the cells against the infection, these antibodies are taken into the cells together with the bound virus; then once inside the cells, the virus starts to multiply like there were no antibodies in the first place, i.e., they are “virus-friendly antibodies” or “harmful antibodies.”

Dr. Kibenge adds, “What this indicates or suggests to us is that some virus proteins or antigens on the ISAV particles induce the production of these harmful antibodies. These antigens must be identified and excluded from ISAV vaccines in order for these vaccines to have substantial preventative value.”

Again, “We are getting close to the point of identifying these harmful antigens,” he says.

Dr. Kibenge is a molecular virologist who began working on ISAV in 1997 following outbreaks in salmon farms in New Brunswick. His research at AVC is funded by Canada’s Natural Sciences and Engineering Research Council (NSERC), and he recently received an NSERC Strategic Research Grant for $762,910 over four years to continue work on ISAV.