Investigation on the incidence of adverse reactions, viraemia and haematological changes following field immunization of cattle using a live attenuated vaccine against lumpy skin disease.

ABSTRACT

The present study was performed to investigate the clinical impact and certain virological and haematological parameters following immunization of cattle against lumpy skin disease (LSD). The study was conducted in a dairy cattle farm (215 animals), immunized with a Neethling strain-based live vaccine. Twenty-seven animals (14 lactating cows, four dry cows and nine calves) were randomly selected for repetitive blood and saliva samplings. An EvaGreen-based real-time PCR was designed to differentiate vaccine from field LSDVs. Vaccinated animals underwent examination for adverse reactions. Nodule samples were collected from two representative cases for histopathological testing and virus identification. Milk yield was calculated based on bulk-tank measurements of all lactating cows (79). Viral DNA was detected between days 6-15 post-vaccination (p.v.) at 63% of the sampled animals (17/27). Saliva and bulk-tank milk samples were LSDV-negative. Pronounced swelling was observed at injection sites of 12% of the immunized animals (26/215), starting at day 6 p.v., and was resolved after 2-4 days. Small-sized (<0.5 cm) cutaneous lumps were developed between days 8-18 p.v. at 9% of the vaccinated animals (19/215). These were observed in adult cows and not in calves/heifers. Resolution was observable 10 days post-development. The vaccine virus was also identified in nodules and injection-site aspirates. Haematological changes (e.g., lower leucocyte counts) were observed in cows and not in calves. Daily milk production was being reduced during the first 12 days p.v. LSD immunization of cows resulted in nodules and low viraemia levels. The fact that nodules and haematological changes were not observed in calves, along with the low viraemia, supports the reduced virulence of the Neethling vaccine strain. The characteristic nodules in vaccinated animals could allow clinical differentiation from those observed in LSD. The developed real-time PCR efficiently differentiates infected from vaccinated cattle, and should be further validated as a tool in LSD surveillance.