Evaluation of the safety of cell culture-adapted fowl pox vaccines

Fowl pox virus infections cause significant economic losses in poultry farming, particularly in endemic regions. Despite the widespread use of chorioallantoic membrane (CAM)-propagated vaccines in Nigeria, outbreaks persist. This study aimed to assess the safety of cell culture-adapted fowlpox virus vaccines in chickens. A total of 25 specific-antibody-negative, five-week-old chickens were vaccinated via the wing web route with ten standard field doses (≈0.12 mL per dose) of each cell culture-adapted vaccine. The birds were monitored for 7–21 days for vaccine “takes,” adverse effects, disease, or mortality. Two birds per group were euthanized on day 21 for histological examination using Haematoxylin and Eosin staining. All vaccinated chickens (100%) developed vaccine “takes” without adverse reactions, disease, or mortality. No vaccine-associated disease or virulence reversal was observed (0%), as histological examination showed no “Bollinger bodies.” However, mild histopathological changes were noted, including renal tubular necrosis, hepatocyte necrosis, hemorrhage, and vascular congestion in various tissues. Polymorphonuclear cell clusters were also found in lung and liver tissues. These findings indicate that cell culture-adapted fowlpox vaccines are safe and effective under laboratory conditions. Additionally, they offer advantages over CAM-propagated vaccines, such as ease of production, cost-effectiveness, and higher vaccine yields. Further studies are needed to validate these results, assess vaccine persistence in host tissues, and evaluate the potential for genetic mutations.