Australia - Scientists crack oyster disease mystery

The mystery of the source of a parasite threatening to cripple the Sydney rock oyster industry may finally have been cracked.

In 2004 an outbreak of QX disease in the Hawkesbury River killed oysters worth $5 million. Although harmless to humans, QX, found from south-eastern Queensland to the Georges River, has killed up to 90 per cent of infected oysters.

Scientists have known since 1976 that QX involves a parasite. However, it cannot migrate directly from one oyster to another and, until now, its origin has left scientists baffled.

In a major biosecurity breakthrough, Queensland Museum researchers have identified a tiny marine worm as the carrier.

Rob Adlard, the museum's head of marine zoology, said yesterday the discovery opened the way for laboratory research to defeat the disease, as well as the development of QX-resistant oysters.

Dr Adlard said scientists had suspected the parasite was being carried in another marine animal, but had had no idea which was the host.

To make the hunt even more difficult, parasites can take on different physical appearances when inside different hosts, meaning researchers armed with microscopes could not even be sure what they were looking for.

"It became a nightmare when you saw just how many possible candidates there were," Dr Adlard said.
His team solved the puzzle using DNA analysis of worms in Hawkesbury River mud.

"Thank God for DNA," said Dr Adlard, admitting he was jubilant when he realised the carrier had been found.

"I was really excited. This is the culmination of 10 years of research - and gut feeling, if you will pardon the pun."

QX was so named because when it was discovered in Queensland scientists could not explain its cause.

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Australia - Scientists crack oyster disease mystery