Oral vaccines hold significant promise for fish farmers due to their ease of administration, especially for small fish that are challenging to vaccinate via injection. However, their effectiveness has been limited, primarily due to the hostile environment of fish stomachs, which can degrade the vaccine components before they take effect.
A recent analysis by scientists in India suggests that innovative stomach-resistant designs for oral vaccines could address this challenge. One approach involves encapsulating oral vaccines to protect them from gastric acids and digestive enzymes. This protective layer aims to ensure that the vaccines reach the hindgut, where immune cells can respond to the antigens and provide protection against target pathogens.
Traditionally, oral vaccines are mixed into fish feed, offering cost and labor savings, as well as stress-free vaccination for fish. However, the protective coating is crucial for overcoming the stomach’s destructive effects.
Among the promising encapsulation options are nanomaterial-based coatings, including chitosan, a biodegradable polymer derived from natural sources like crustacean shells. Early studies have shown stability in stomach acid and release in the intestine for such coatings.
Another approach involves delivering vaccines through live feed, such as artemia, daphnia, and rotifers. These “bioencapsulated” vaccines are not only stomach-resistant but also suitable for fish larvae, which are too small for injection. They have demonstrated effectiveness in reducing bacterial and viral infections in fish larvae.
Looking ahead, researchers are exploring various coating options, including algae-based biopolymers and liposomes, as well as engineered microorganisms like yeast for vaccine delivery.
The future of oral vaccines in aquaculture holds promise, potentially enabling mass vaccination through live feeds. This approach could offer cost savings compared to injection and immersion immunization methods while improving efficacy. To enhance the effectiveness of oral vaccines, further research is needed to optimize dosage, antigen nature, formulations, immune response processes, and the ideal age for vaccinating different fish species.
