Evaluation of the effect of applying a specific diluent on efficacy and effectiveness of Fowl Pox vaccine

Providing a standard diluent for preparing the lyophilized Fowl Pox vaccine not only facilitates the preparation of the vaccine for inoculation and improves the accuracy of vaccination but can also affect the effectiveness of the vaccine. The aim of the present study was to investigate the role of a standard diluent in the preparation of the Fowl Pox vaccine and its effect on virus stability in the ready-to-use vaccine, vaccine efficacy, and effectiveness in field conditions. In this study, a colored diluent specifically prepared for the Razi poultry Fowl pox vaccine was evaluated and compared with conventional diluents recommended by vaccine producers. In the first experiment, the vaccine titer stability was investigated at 0, 12, and 24 hours after vaccine preparation by different diluents including specific diluent, distilled water containing 20% (V/V) of glycerin and PBS (Phosphate-buffered saline), as the positive control. In the second experiment, the efficacy of the vaccine prepared with a specific diluent, distilled water containing 20% (V/V) of glycerin, an imported diluent (containing water for injection), was evaluated following a challenge with the virulent Fowl Pox virus. In the third experiment, the effectiveness of the vaccine prepared with specific diluent or distilled water containing 20% (V/V) of glycerin was studied. The results of the first experiment showed that the use of a specific diluent or distilled water containing 20% glycerin could help to maintain vaccine titer during the post-preparation period compared to PBS (P <0.05). The results of the second experiment revealed that under the controlled laboratory conditions, there was no difference between the experimental diluents in terms of vaccinal take and vaccine efficacy in preventing post-challenge acute disease (P>0.05); however, all the vaccinated groups had higher vaccinal take and protection compared to the positive (inoculation of specific diluents without vaccine) and negative (inoculation of no vaccine and diluent) control groups (P<0.05). In the field trial experiment, the vaccinal take associated with the specific diluent group was 11% higher than the positive control group (P<0.05). In general, the findings of this study showed that the application of a specific diluent for preparing the Fowl Pox vaccine, not only maintains its maximum efficacy but also it has advantages over conventional diluents in terms of applying easiness and improving the vaccine effectiveness.