Chitosan nanoparticle vaccine loaded with crude extracellular proteins of C. perfringens and Salmonella flagella is partially protective against necrotic enteritis in broiler chickens.

Abstract

Necrotic enteritis (NE) causes significant economic losses and food shortages world-wide. There are currently no licensed commercial vaccines against NE in broilers. Chitosan nanoparticles were formulated with extracellular proteins of C. perfringens surface-tagged with Salmonella flagellar proteins. One-day-old male broiler chicks were completely randomized to 3 treatments: Non-vaccinated non-challenged as negative control, Vaccinated-challenged, and non-vaccinated challenge as positive control. On day of hatch, d7, and d14 post-hatch, vaccinated-challenged birds were orally gavage with 50g vaccine in 0.5ml PBS while positive control birds were gavage with 0.5ml PBS only. Birds in the vaccinated-challenged and positive control groups were orally infected on d14 post-hatch, with 5,000 oocysts/bird of E. maxima, followed by log 8 CFU of a virulent strain of C. perfringens on d19, d20, and d21 post-hatch. From d14 to 21 and d14 to 28 post-hatches, mortality in the vaccinated-challenged group was higher than that in the positive control group, approaching statistical significance (p=0.07). On d21 post-hatch, the mean lesion score of 3 birds/cage in the vaccinated-challenged group was higher than the positive control group, approaching statistical significance (p = 0.05). From d 14 to 28 post-hatch, the feed intake was higher and feed conversion ratio lower in the vaccinated-challenged group compared to the positive control group (p<0.05). On d21 post-hatch, antigen specific recall proliferation in the vaccinated-challenged group was higher than that in the negative and positive control groups (p<0.05). On d21 post-hatch, cecal tonsils CD8+ T lymphocytes expression in the vaccinated-challenged group was similar to the negative control group (p>0.05) but higher than that in the positive control group (p<0.05). Finally, vaccination resulted in an increase in ileal mRNA levels of zonula occluding on d21 post-hatch. In conclusion, there were numerical but not statistically significant decrease in NE lesions and mortality in vaccinated and challenged broilers. Further studies are needed to improve the efficacy of the vaccine and understand the mechanism underlying protection in vaccinated birds.