Fish vaccines keep antibiotic risk at bay

It is more effective than antibiotics and benefits consumers' health too, but costs are higher for farms
Audrey Tan Straits Times 20 May 17;

Just as infants are vaccinated against certain diseases, young fish at three farms here are also getting the same treatment.

They are injected with vaccines instead of being fed with antibiotics, the usual practice currently.

This keeps the fish - and the humans who eat them - healthy. This is because vaccines reduce the risk of people developing a resistance to antibiotics.

When farmed animals, such as fish, are fed with antibiotics, there is the possibility of residual drugs passing through the food chain and ending up in the bellies of humans, said Emeritus Professor Hew Choy Leong from the National University of Singapore's (NUS) department of biological sciences.

"Many of these antibiotics are used to treat human diseases. If antibiotics are consumed excessively, the bacteria can develop a resistance to medicine that was previously able to kill them," he said.

Only three of some 120 fish farms here have started vaccinating their fish, but experts hope more will follow. Fish farm Marine Life Aquaculture, for example, started a pilot to swop antibiotics for vaccines about four years ago.

Its managing director Frank Tan said the pilot has been successful - 90 per cent of vaccinated fish survived, compared with 20 per cent of those fed with antibiotics.

The farm will scale this up from next month to all its fingerlings, or young fish about 10cm long.

"When we vaccinate the fish, there is herd immunity which prevents disease from spreading fast - important for farmed fish in close proximity to one another. Antibiotics are mainly used after a bacterial infection hits, and it may be too late," said Mr Tan.

Vaccines cost twice as much as antibiotics, and administering them is labour-intensive - workers have to manually vaccinate the fish one by one - but Mr Tan said the high survival rate was worth it.

The Straits Times reported last December that the Health Ministry was working with the Agri-Food and Veterinary Authority (AVA), the National Environment Agency and NUS on a nationwide strategy to tackle the problem of some bacteria becoming increasingly resistant to antibiotics.

"Due to increasing worldwide concerns over the development of antimicrobial resistance, AVA has been stepping up efforts to advise and educate our farmers on proper fish health management to prevent infections without using antibiotics, and (on) prudent drug usage to treat disease when needed," an AVA spokesman told The Straits Times.

Farmers must follow certain procedures which, among other things, will prevent residual antimicrobials from exceeding certain levels, she said.

Whether more farms would start vaccinating their fish depends on factors such as cost, said Dr Grace Loo, a lecturer in marine science and aquaculture at Republic Polytechnic's School of Applied Science.

Dr Dirk Eichelberger, from fish farm Singapore Aquaculture Technologies, believes vaccines are key as they improve survival rates.

"However, there is a shortage of suitable vaccines in Singapore, and those that are available require a very high minimum order quantity," he said, adding that he uses antibiotics only in the rare event of disease outbreaks.

AVA said farms can tap its Agriculture and Productivity Fund to buy equipment, such as those required for fish vaccination, that boosts productivity.

Service executive Julie Ng, 60, said she is keen to buy vaccinated fish. "It sounds like the healthier choice, and why not, if the fish are cheaper too."

But teacher Ho Heng Mei, 56, said fresh fish are not sold with nutrition labels, making it hard for consumers to differentiate between vaccinated fish and fish fed with antibiotics. "There is no way to know the treatment process given. So as long as there is no health warning, I will continue to enjoy eating fish."

Why vaccines work better than antibiotics

Give a man a fish and he feeds for a day. Teach a man to fish and he feeds for a lifetime. That is essentially what antibiotics and vaccines do respectively.

Antibiotics are chemical compounds designed to kill bacteria - they treat a disease when it happens. Vaccines, on the other hand, are preventive. They contain biological compounds that bolster the body's own immune system to protect it against specific pathogens.

Mr Lee Yeng Sheng, a senior specialist for global marketing in aquaculture at MSD Animal Health, which developed the vaccines used by local fish farm Marine Life Aquaculture, said fish vaccines work like human vaccines. "Once administered, the fish will mount a natural immune response and be protected from infection by the disease, allowing for the use of medicines such as antibiotics when only absolutely necessary," he said.

This means that the next time a fish encounters an infection caused by bacteria or viruses it has been vaccinated against, its immune system will be ready to fight it. But if it had been given antibiotics instead, a new dose would be required every time there is an outbreak.

This could encourage and breed resistance in the bacteria, said Dr Leong Hoe Nam, an infectious diseases specialist at Mount Elizabeth Novena Hospital.

When fish are given antibiotics, the chemicals are usually mixed in its food.

"When the antibiotics go directly into the sea, or are excreted by the fish into the sea, it provides sub-therapeutic levels of the drug - which means the dosage is lower than that required to kill the pathogen," said Dr Leong. This makes it easy for the bacteria to mutate against the drug - an effect that vaccines do not have on the pathogen.

"In other words, give the fish antibiotics, you rid the bacteria for one day. Give the fish a vaccine, you teach the fish to fight the bacteria every day," he said.

Audrey Tan