Experimental study of Forsythoside A on prevention and treatment of avian infectious bronchitis

Forsythoside A is the main active ingredient in the Chinese medicine Forsythia suspensa, which has antiviral, anti-inflammatory, antioxidation, and immunoregulatory effects. It is reported that Forsythoside A can significantly inhibit the replication of the avian infectious bronchitis virus(IBV) in cells, but there is no report in chickens. The present study aimed to investigate the effect of Forsythoside A on IBV-M41, experiments were designed using 120 chickens at 12 days of age. The chickens were randomly divided into eight groups: Forsythoside A high-, medium-, and low-dose prevention groups, Forsythoside A high-, medium-, and low-dose treatment groups, model control group and normal control group. All chickens, except the normal control group, were inoculated with 0.2 ml of IBV-M41 at 15 days of age.The antiviral effects were evaluated by clinical signs, weight, histopathology, T-,B-lymphocyte proliferation, T-lymphocyte subsets and cytokine levels.The results showed that the infection rate in each Forsythoside A prevention group was significantly lower than that in the treatment group and model control group (P < 0.05). The recovery rate in each Forsythoside A treatment group was significantly higher than that in the model control group (P < 0.05), and the recovery rate in high- and medium-dose treatment group was the highest, at up to 86.67%. Lymphocytic transformation ability significantly improved in the prevention and treatment groups. Forsythoside A significantly improved the CD3+, CD4+, and CD8+ T-lymphocyte of infected chickens. The cytokine level was able to maintain high concentrations of IL-2 and IFN-α for a long time and maintain a dynamic IL-4-concentration balance. A number of results showed that Forsythoside A had both preventive and therapeutic effects in IBV-M41-infected chickens, among which the high-dose (80 mg/kg/d) prevention group，the high- (80 mg/kg/d) and medium (40 mg/kg/d) -dose treatment group had significant effects.