Kathy La Fauce and the cricket that
helped her to develop the vaccine.

Researchers at James Cook University have developed a virus ‘silencing’ technique that could save the Australian prawn industry from millions of dollars in losses.

PhD student Kathy La Fauce has spent three years investigating how to reduce the spread of a virus which is robbing Australian aquaculture farms of their prawns.

Penaeus merguiensis densovirus (PmergDNV) is the Australian strain of hepatopancreatic parvovirus, which stunts the growth of prawns, leaving them vulnerable to other infections, and often results in death.

Currently prawns cannot be vaccinated against any virus, so if a pond is infected the farmer has to put up with the losses, dry out the pond and re-stock.

Through RNA interference – a gene ‘silencing’ mechanism that occurs naturally in plants and animals – Kathy has been able to identify the virus genes responsible for the replication of PmergDNV within an animal and, thanks to an orchestra of crickets, has developed a method to reduce its ability to replicate.

“Prawns carry other viruses which affect the results of my experiment so we moved to insects as a model because of their identical biosynthetic machinery,” said Kathy. “Densoviruses are also known to occur in crickets so they were the obvious choice.”

By cloning a sequence of the replicating gene of PmergDNV and injecting it into a cricket, Kathy has been able to protect it against future infections with the live virus.

“The copied sequence binds to the same sequence in the live virus and the infected animal’s enzymes destroy it, which stops or ‘silences’ gene expression and prevents the animal suffering any of the affects of the virus,” she said.

The technique could have massive implications not only for the Australian aquaculture industry but for the international industry.

“We knew this virus was in farms but didn’t know what impact it was having on prawns so we scanned 190 ponds – 28.5 thousand larvae – between 2007 and 2008. We estimated that by reducing the levels of PmergDNV using this new technique, productivity could increase by at least 14 per cent. The Queensland industry makes $46.5million each year, so that’s an increase of $6.5 million if farmers are growing susceptible species.”

The next step is to work out how to deliver the sequenced PmergDNV gene into thousands of prawns at a time.

“We think we can grow it in bacteria, put it into food and let it reproduce thousands of times over – that way, the prawns will eat the food and at the same time ingest the sequenced gene,” said Kathy.