Efficacy of an anticoccidial live vaccine in prevention of necrotic enteritis in chickens.

Necrotic enteritis (NE) is an important disease in poultry caused by Clostridium perfringens combined with predisposing factors, mainly eimeriosis. In the present study, we investigated the protective effect of a commercial attenuated anticoccidial live vaccine against NE in a clinical infection model using 60 day-old chicks. Vaccination was performed on study day (SD) 1 with natural booster-infections for 4 weeks from Eimeria spp. oocysts present in litter. On SD 28, five groups were formed (n=12): group V+/C-E- (vaccinated, uninfected), group V+/C-E+ (vaccinated, infected with Eimeria spp.), group V+/C+E+ (vaccinated, infected with clostridia and Eimeria spp.), group V-/C+E+ (unvaccinated, infected with clostridia and Eimeria spp.), and group NC (negative control). Efficacy was measured by clinical parameters, pathogen multiplication, and pathological parameters assessed during two necropsies on SD 34 and SD 40, respectively. Additionally, cytokine expression was measured in gut and spleen tissues at necropsy. Clinical signs of NE were observed only in the coinfected groups, mainly in group V-/C+E+. Accordingly, lowest body weight gain was observed in group V-/C+E+ (301.8 g from SD 28 to SD 40; group NC: 626.2 g). Oocyst excretion varied significantly (P<0.01) between all Eimeria spp. infected groups and was highest in group V-/C+E+, followed by V+/C+E+, and lowest in group V+/C-E+. NE typical intestinal lesions showed only in groups V+/C+E+ and V-/C+E+. The intestinal mucosa featured partly severe lesions in the jejunum, C. perfringens colonization was histologically visible. Upregulation of IFN-γ, was observed in the jejunal tissue of group V-/C+E+ (P<0.01 (SD 34) or P<0.05 (SD 40) compared to all other groups). IL-10 and IL-12 were upregulated in group V-/C+E+, IL-10 also in group V+/C+E+ (SD 40) while IL-2 expression remained unaltered. In conclusion, vaccination against coccidiosis was effective in preventing NE in a mixed infection comparable to field situations.