Humoral Response in Cattle Vaccinated with the Heterologous Sheeppox Virus Vaccine for Protection Against Lumpy Skin Disease: A Field Study.

BACKGROUND/OBJECTIVES: Lumpy skin disease (LSD) is a notifiable disease due to a marked potency for rapid spread and a significant negative economic impact on agriculture worldwide. As such, vaccination is considered the most effective way to control the disease in endemic countries, and the serological response to homologous LSDV-based vaccines is widely investigated. However, less is known about the seroconversion and duration of the immune response that is elicited by live attenuated heterologous vaccines based on the Sheeppox virus (SPPV) used for LSD prevention. This study aimed to investigate the humoral immune response in cattle immunized with a heterologous SPPV-based vaccine in the field. METHODS: Commercial ELISA, based on P32 protein, as well as immunoblotting, were used to assess the antibody response in 6-month-old, 17-month-old, and older animals before and after the first immunization and revaccination. RESULTS: Only a secondary immune response was detected when using commercial ELISA in revaccinated animals in each of the groups (83.3% and 30%, respectively). A comparative bioinformatic analysis proved a marked polymorphism of P32, derived from LSDV/SPPV/GTPV, which potentially resulted in negative responses in the ELISA. However, immunoblotting revealed a 100% seroconversion in vaccinated animals after the first vaccination and revaccination. Notably, specific antibodies were found in the sera of 80% of 6-month-old calves before the first vaccination, which had probably been passively transferred from their mothers, who were multiply vaccinated with SPPV-based vaccines. CONCLUSIONS: Several immunodominant antigens were able to induce a humoral immune response in cattle to the SPPV-based vaccine after passive and active immunization, serving as promising markers for a humoral immune response to heterologous vaccines.