Dr Joebert D Toledo considers fish diseases hamper the booming aquaculture industry. (Photo: SEAFDEC-AQD)
Scientists test vaccine to halt viral infections in farmed fish
Friday, September 09, 2011, 15:20 (GMT + 9)
Filipino scientists are testing a vaccine to make farmed species immune to the lethal Viral Nervous Necrosis (VNN) virus. VNN can wipe out entire crops and cause enormous economic losses.
"The emergence of fish diseases caused by viruses, bacteria and other parasites is one of the downsides of the booming aquaculture industry," said Dr Joebert D Toledo, who heads the Southeast Asian Fisheries Development Centre Aquaculture Department (SEAFDEC-AQD).
SEAFDEC’s vaccine is being tried in broodstock so they can breed offspring free from the virus. The move is significant because it is believed that national VNN outbreaks are caused by the transmission of the virus from VNN-positive broodstocks to their offspring, said Dr Rolando V Pakingking Jr, a virologist at SEAFDEC’s Fish Health Section.
His research shows that a single injection with a formalin-inactivated vaccine provokes powerful immune responses and considerable protective immunity in experimental sea bass, grouper and pompano exposed to the virus, Malaya reports.
When the formalin-inactivated vaccine was given to infected fish in a laboratory, the vaccine induced protective antibodies that work to protect against the VNN virus with a 90 to 100 per cent survival rate.
In grouper, antibodies offered protection even up to six months, which is how long it usually takes to raise grouper until harvest. Ongoing experiments with pompano fish cage culture are also proving successful.
"It shows that antibodies can easily be activated to act against the virus so that it cannot infect the nerve cells anymore, making the fish resistant or less vulnerable to VNN," Pakingking said, adding that the findings suggest "that a single vaccination is enough to confer immunity and mount protection against the VNN virus in fish reared in cages in the natural marine environment where the virus is ubiquitous."
Preventive measures include screening broodstock, eggs and larvae for the virus by reverse transcriptase polymerase chain reaction, a lab technique often used in molecular biology to diagnose diseases and study viruses. However, at PHP 950 (USD 22.39) per test, the expense is too high for mass screening.
"With screening, VNN can be controlled in the nursery through elimination of VNN positive breeders and larvae," he said. "But the problem occurs when fish is reared in the natural environment like open floating cages where the virus can be easily transmitted to other fishes."
Vaccination is the way to go, he insisted.
By Natalia Real