Infectious Disease in Aquaculture by B Austin

Author:B Austin [Austin, Brian]
Language: eng
Format: epub
ISBN: 9780857090164
Publisher: Elsevier
Published: 2012-09-15T05:00:00+00:00

10.4.4 Poly(lactide-co-glycolide) (PLGA) particles

Nano- and microparticles can be used to improve the antigenicity of weak antigens and thereby act as adjuvants (Morris et al. 1994). The encapsulation of vaccines in biocompatible and biodegradable PLGA polymers has been studied for over 20 years. Antigen is released from the microspheres by diffusion through matrix pores and by matrix degradation. Biodegradation rates can be regulated by alterations in polymer composition and molecular weights.

To date, only a few studies have been carried out on fish with regard to uptake and degradation of PLGA particles and the immune response obtained. For the most part these studies have focused on oral administration (O’Donnell et al. 1996; Lavelle et al. 1997; Tian et al. 2008; Altun et al., 2010; Tian and Yu 2011). Recently, an article has been published which reported on parenteral immunisation of a major Indian carp species, rohu (Labeo rohita), with a PLGA-encapsulated antigen (Behera et al. 2010). Outer membrane proteins (OMPs) of A. hydrophila were encapsulated in PLGA microparticles. OMPs were mixed with FIA in an emulsion, and OMPs alone were i.p. injected in rohu. The antibody titres 21 and 42 days post-immunisation were significantly higher in the PLGA-encapsulated antigen group and in the FIA group compared with the OMP group (Behera et al. 2010). No significant differences in antibody titres were found between the FIA and PLGA groups.

Oral vaccines encapsulated in PLGA have been used in Japanese flounder (Tian et al. 2008; Tian and Yu 2011) and salmonids like rainbow trout (Lavelle et al. 1997; Altun et al. 2010) and Atlantic salmon (O’Donnell et al. 1996). The Japanese flounder, an important aquacultured species, is suffering from infection with lymphocystis disease virus (LCDV). A plasmid encoding the MCP of LCDV was constructed and encapsulated in PLGA. Controls were naked plasmid vaccine and blank PLGA particles (Tian and Yu 2011). The fish were orally intubated, and 28 days post-vaccination the fish were challenged by i.m. injection with LCDV. Vaccine effects were evaluated by observing the presence of lymphocystis nodules. The cumulative percentage of Japanese flounder with nodules after challenge was greatly reduced in the group receiving the plasmid coding for the LCDV protein in PLGA particles in the period between 15 and 120 days postimmunisation (Tian and Yu 2011). The MCP was expressed in tissues of fish vaccinated with plasmid DNA (pDNA) particles. In addition, the levels of antibody in the sera of fish vaccinated with PLGA microcapsules increased until 9 weeks post-immunisation, and then started to decrease (Tian et al. 2008).

In rainbow trout, human gamma globulin (HGG) was microencapsulated in PLGA (Lavelle et al. 1997). Specific antibodies were detected in the intestinal mucus of fish that had been administered with the microencapsulated antigen after boosting with soluble HGG, but not in fish that had been primed with the soluble antigen. The fate of orally administered free and encapsulated HGG has also been determined in Atlantic salmon. At 15 min after administration, the HGG–PLGA was found in the intestine, resembling the observation for free HGG (O’Donnell et al.

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