October 28, 2008


Australian researcher discovers new technique to 'silence' prawn virus

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


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


Currently prawns cannot be vaccinated against any virus, which makes farmers extremely vulnerable to losses.


However, through RNA interference, a gene "silencing" mechanism that occurs naturally in plants and animals, researcher Kathy La Fauce was able to identify the virus genes responsible for replication of PmergDNV within an animal. Also, crickets had enabled her to develop a method to reduce the virus' 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 La Fauce, "Densoviruses are also known to occur in crickets so they were the obvious choice."


By cloning a sequence of the replicating virus gene and injecting it into a cricket, La Fauce was 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 virus effect, according to La Fauce.


By reducing the levels of PmergDNV using this new technique, productivity could increase by at least 14 percent, La Fauce said.


"The Queensland industry makes US$46.5million each year, so that’s an increase of US$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.


La Fauce said they could grow the sequence in bacteria, put it into food and allow it to reproduce thousands of times over – in that way, the prawns will consume the feed and at the same time ingest the sequenced gene.

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