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The amount of vaccine remaining on the skin surface post-vaccination with the needle-free method suggested that further studies of needle-free injections could lead to establishment of much smaller effective vaccination doses with this system.

Summary

This study, carried out at the University of Saskatchewan.s Vaccine & Infectious Disease Organization (VIDO), evaluated commercial vaccine delivery to piglets using a low-pressure, needle-free jet injector against intra-muscular delivery and found that resulting immunity in needle-free animals was as good or better than that developed by animals immunized using a syringe and needle. Animals immunized with the needle-free jet injector also experienced milder clinical disease. This work confirmed similar results achieved by researchers using other drugs or vaccines.

Introduction

Vaccination of livestock is crucial to developing specific immune resistance to diseases that otherwise cost producers billions of dollars. Vaccination of livestock with needles - intramuscular and subcutaneous - can incur costs through animal stress, vaccine residues, injection site lesions and broken needles. Needle-free injection offers several benefits over traditional means. Vaccine is dispersed as minute particles in skin and other tissue, greatly increasing exposure to white blood cells, and thus improving vaccine uptake. Entry points are minute, minimizing tissue damage at the injection site. The injector can be loaded for multiple injections and needle stick injuries are eliminated.

Experimental Procedures

Piglets were housed under commercial conditions for their initial five weeks, then transported to VIDO where they were housed in a controlled-temperature and ventilation isolation room with free access to water and commercially prepared feed. Piglets of six and nine weeks of age were vaccinated with Pleurostar-APPâ either by needle-free jet injector (NF) administration at 220 psi or conventional intra-muscular (IM) routes (eight piglets each).

Piglets receiving the vaccine by IM routes were injected at the right (primary injection) or left (booster) neck muscle with a 1x18 ga needle. For the NF group, the vaccine was delivered to the same surface location. Amounts of vaccine remaining on skin surface were quantified.

Blood samples for serological studies to quantify immune reaction were collected at the time of first vaccination, second vaccination, and pre-challenge (days 0, 21 and 28 respectively). At ten weeks of age groups of pigs from each treatment were challenged for 10 minutes with Actinobacillus pleuropneumoniae via aerosol in an enclosed plexiglass chamber. Pigs were clinically observed for seven days post-challenge and lung tissue analyzed for presence of A. pleuropneumoniae lesions.

Results & Discussion

An adverse clinical event in response to vaccination and blood sampling during the study was not related to the vaccination process.

All vaccinated pigs exhibited at least a four-fold increase in antibody titre before challenge. Measurement of two indicators of immune response (IgG1, IgG2) showed parallel immune reactions to A. pleuropneumoniae antigen OmIA for both groups (NF and IM) (Figure 1). Both groups also showed parallel immune responses for a second A. pleuropneumoniae antigen, ApxII (Figure 2).

The amount of vaccine remaining on the skin surface after vaccination was almost 60-fold greater for NF treatment; however the NF was used in this study without optimization for skin penetration. In terms of clinical disease, both groups of pigs were protected, and clinical disease was significantly milder in the NF group.

Acknowledgements

Program funding and support was provided by WLT Distributors Inc., Manitoba Pork Council, Sask Pork, Ontario Pork, Alberta Pork, and the Canadian Research Network on Bacterial Pathogens of Swine.

Source: Manitoba Pork Council - September 2004