A Safer Alternative for the Development of Oral Vaccines for Shrimp

Shrimp aquaculture has long struggled with devastating viral diseases, particularly White Spot Syndrome Virus (WSSV). These diseases can cause significant mortality rates, leading to substantial economic losses. While vaccination shows promise as a preventive measure, traditional methods often face limitations, particularly in of istration and efficacy.

A recent study published in Aquaculture introduced an innovative approach to shrimp vaccination, leveraging a safe and effective bacterial delivery system. By using heat-killed attenuated Listeria monocytogenes (HKALM), researchers from Seeing Bioscience Co., Ltd., Innocreate Bioscience Co., Ltd., National Taiwan Ocean University, Monash University, and National Taitung University have developed a new oral vaccine capable of effectively delivering genetic material to shrimp, triggering a robust immune response.

Disease Management Strategies

Disease management strategies in aquaculture include antibiotics, chemotherapeutics, probiotics, and vaccination. However, antibiotics and chemotherapeutics are increasingly criticized due to risks such as drug residue accumulation, the emergence of resistant pathogens, and potential immunosuppression.

Vaccination is a promising alternative, though its widespread application is limited by the lack of cost-effective and scalable delivery systems, particularly for oral istration.

Vaccination in Shrimp

Shrimp lack adaptive immunity but can mount innate immune responses against bacteria, parasites, and viruses, driving research into shrimp-specific vaccines. Despite efforts to develop vaccines using inactivated pathogens, recombinant proteins, DNA, and RNA interference techniques, current approaches offer limited protection and are impractical for immersion or oral delivery.

Live attenuated bacteria such as Salmonella, Shigella, Yersinia, and Listeria monocytogenes have been investigated as DNA vaccine carriers due to their ability to invade host cells and deliver plasmids with minimal risk of reverting to virulent strains. Among these, L. monocytogenes is a well-established platform for delivering therapeutic macromolecules and DNA, demonstrating versatility in aquatic and mammalian models.

A Triple-Layered Safety Approach

To ensure safety for both the environment and the target organisms, researchers implemented a rigorous triple-layered safety strategy:

1. Bacterial attenuation: Listeria monocytogenes bacteria were genetically modified to be less virulent, reducing their disease-causing potential.
2. “Suicide” mechanism: A self-destruction mechanism was incorporated into the bacteria, ensuring they would not persist in the environment.
3. Heat killing: The bacteria were further inactivated through heat treatment, eliminating any residual infection risk.

Effective Gene Delivery and Immune Stimulation

The HKALM delivery system demonstrated impressive efficiency in delivering genetic material to shrimp hemocytes and intestinal cells. Using green fluorescent protein as an indicator, researchers visualized and quantified gene expression, confirming successful vaccine delivery.

Moreover, when the WSSV envelope protein VP53A was expressed via HKALM, it significantly enhanced shrimp immune response, as evidenced by increased phenoloxidase activity. This enhanced immune response translated to improved survival rates following WSSV infection.

A Promising Future for Shrimp Aquaculture

This innovative approach to shrimp vaccination offers several advantages over traditional methods:

• Oral delivery: The oral delivery system is easy to ister and eliminates the need for invasive injection techniques.
• Enhanced safety: The triple-layered safety approach minimizes risks of environmental contamination and adverse effects on shrimp.
• Effective immune response: The HKALM delivery system triggers a strong immune response, providing robust protection against viral diseases.

Conclusion

The study findings suggest that HKALM provides a safer, more effective, and scalable platform for developing oral vaccines in shrimp aquaculture, offering a promising solution for managing WSSV and other viral diseases.

Key Findings:

• HKALM is a safer alternative for oral vaccine development in shrimp aquaculture.
• The triple-layered safety approach minimizes environmental risks.
• HKALM effectively delivers plasmids to shrimp hemocytes and intestinal cells.
• Expression of the WSSV VP53A envelope protein via HKALM improves shrimp survival rates following WSSV infection.

By addressing critical challenges in shrimp aquaculture, this groundbreaking research paves the way for a more sustainable and resilient shrimp farming industry. As scientists continue to refine this technology, we can expect significant improvements in shrimp health, productivity, and overall economic viability.

The study was funded by the National Science and Technology Council.

Li-Li Chen
Institute of Marine Biology, National Taiwan Ocean University
No. 2, Pei-Ning Road, Keelung 20224, Taiwan, ROC.
Email: [email protected]

Reference
Hsu, J. C. K., Hsu, T., Guan, S., Chi, P., Chiang, C., Pouton, C. W., Wong, Z., Huang, P., & Chen, L. (2025). Development of an oral vaccine delivery system for shrimp aquaculture using attenuated Listeria monocytogenes. Aquaculture, 597, 741940. https://doi.org/10.1016/j.aquaculture.2024.741940