Vaccine giving oyster lovers hope | 7.30

Key Concepts

• Pacific Oyster Mortality Syndrome (POMS): A herpes virus affecting Pacific oysters, causing high mortality rates.
• QX Disease: A parasitic disease affecting Sydney Rock oysters.
• Natural Immunity: The development of resistance to POMS in some oysters after exposure.
• Vaccination (Oysters): A novel approach to protecting oysters from viral diseases, initially demonstrated with POMS.
• Plankton: Microscopic organisms that oysters feed on, and which can carry the POMS virus.
• Mortality Rates: The percentage of oysters dying due to disease, used as a key metric in the study.

Oyster Disease Outbreak and Vaccine Development in the Hawkesbury River

The Hawkesbury River north of Sydney is experiencing significant losses in oyster harvests due to Pacific Oyster Mortality Syndrome (POMS), a herpes virus. Oyster grower John Stubs recounts a devastating event in 2013 where 10 million oysters died “overnight,” resulting in the complete loss of his business. He describes the visual impact as a “cloudy formation throughout the lease of mortality,” with rapid and widespread death across oyster beds.

POMS: The Disease and its Spread

POMS is carried in plankton, the microscopic organisms oysters consume. The disease is linked to warmer ocean temperatures and has spread globally, with “explosive outbreaks” initially observed in France and then across Europe, extending to Scandinavia. The virus manifests in three ways: oysters that are dead with fresh meat, those that are dead and empty (no meat remaining), and those in an intermediate state.

Research Methodology and Initial Findings

Researchers, led by Franciscoca Samson and supported by Richard Wittington, are meticulously studying the disease. Their methodology involves collecting oyster baskets, counting live and dead oysters, and analyzing samples in the lab. A recent field study revealed a 60% mortality rate in one location. Initial dogma suggested oysters, considered “primitive animals” lacking a complex immune system, couldn’t respond to vaccination. However, the team observed that some oysters consistently survived annual outbreaks, leading to the hypothesis of developing natural immunity, particularly during cooler months.

The Vaccine Breakthrough

This observation spurred the development of a vaccine. The team successfully demonstrated that introducing a live virus into oysters could result in survival, achieving “between 86 and 93% survival.” Franciscoca Samson recounts the excitement of the breakthrough, stating, “It was very surprising to see it in front of your eyes…it is way exciting.” This success builds upon Richard Wittington’s prior research into oyster diseases.

Scalability and Future Applications

While individual oyster injection is impractical, the researchers are exploring scalable delivery methods. Potential solutions include coating oyster feed (algae) with the vaccine or directly introducing it into the water. This technological advancement establishes a precedent for vaccination in aquaculture, mirroring practices common in other animal farming systems.

The success with POMS opens possibilities for addressing other oyster diseases, specifically QX disease, which affects Sydney Rock oysters. QX is caused by a parasite, making vaccine development more challenging, but not impossible. John Stubs notes that a QX vaccine would be a “big game changer” for New South Wales oyster farming. He has already removed his Sydney Rock oyster crop to prevent QX infection.

Safety and Conclusion

The researchers emphasize that these viruses are specific to mollusks and pose no threat to human health. The development of a POMS vaccine represents a significant step forward in protecting oyster populations and securing the future of the oyster industry. The research demonstrates the potential for proactive disease management in aquaculture through vaccination, and lays the groundwork for tackling other devastating oyster diseases like QX.