Safety and Efficacy of a Contagious Bovine Pleuropneumonia Inactivated Vaccine Formulated With Different Adjuvants

Abstract

Contagious Bovine Pleuropneumonia (CBPP) is a respiratory disease of cattle caused by Mycoplasma mycoides subspecies mycoides Small Colony (MmmSC) and is mainly controlled by quarantine and vaccination using live MmmSC T1/44 and T1-SR strains. These vaccines while requiring cold chain for delivery, only provide protection for short durations, are unstable after reconstitution and are associated with post-vaccinal site reactions. This study assessed the safety, and protection threshold of an inactivated T1/44 MmmSC vaccine formulated in different adjuvants. Cattle were randomly assigned into 7 groups of 10 animals and the experimental group vaccinated with different inactivated formulations. Animals in the negative control group were vaccinated with either adjuvant alone or Phosphate Buffered Saline, while the positive control group received the current live attenuated T1/44 vaccine. Twenty additional cattle were intubated and served as pathogen donors during the challenge experiment. After vaccination, no animal recorded fever, while the number of animals with swellings at the vaccination site were significantly higher (P<0.001) in the groups vaccinated with the inactivated vaccine formulations compared to the positive control group (T1/44 vaccine). Sero-conversion rates following vaccination were higher in groups that received the inactivated vaccine (KE2 and KE6). After challenge, a significant proportion of animals which received the inactivated vaccine formulations, developed fever and gross pathological lesions characteristic of CBPP, this compared to the live attenuated vaccine. Overall, the protection rate for animals which received the live attenuated T1/44 vaccine was higher. The results demonstrated that inactivated vaccine formulations although safe, did not provide protection levels similar to the current live attenuated T1/44 vaccine. There is need to explore alternative vaccine formulations and booster immunization regimes.