The Efficacy of Conventional and Modified Contagious Bovine Pleuropneumonia T1 44 Vaccines Sixteen Months Post Vaccination

Abstract

Contagious Bovine Pleuropneumonia (CBPP), caused by Mycoplasma mycoides subsp. mycoides biotype Small Colony (MmmSC) is a cattle respiratory disease. It is controlled using live vaccines, movement control and slaughter of affected cattle. The current CBPP vaccine, T144 is associated with several limitations that make delivery in the field difficult. One of main short comings is low efficacy and sub-optimum bacterial titers. This has necessitated modifications in formulation of the vaccine. The current study sought to compare the protection of cattle at sixteen months post-vaccination by T144 vaccine prepared in the media in current use and the mediamodified to improve the vaccine efficacy. The modifications include, use of a buffer system based upon Hydroxyethyl Piperazine Ethanesulfonic Acid (HEPES), incorporation of a simple pH indicator to the culture medium and reconstitution of the vaccine culture in buffered saline instead of 1M MgSO4 as is common practice. Ninety zebu cattle were obtained from a CBPP free a and divided into two groups. One group of 46 cattle was used in a preceeding study to determine the efficacy of the two T144 vaccine formulations at 3 months post vaccination. In the current study the remaining 44 cattle were divided into 3 groups. One group (control group) was given phosphate buffered saline while the other two groups were vaccinated with conventional vaccine and modified vaccine respectively. Challenge was performed 16 months after vaccination by endobronchial intubation using 60 ml of pure culture of the pathogenic MmmSC strain B237. For the first three months following vaccination the animals were bled once per week and on monthly basis thereafter. Serum was analyzed by the complement fixation test (CFT) and the competitive enzyme linked immunosorbent assay (c-ELISA) test. Efficacy of each vaccine was determined by comparing the disease outcome of the vaccinand control groups. The analysis was at 0.05 confidence level. In vitro results show that at the same storage temperature, titers of the modified vaccine were higher than those of the conventional vaccine. This difference was significant including at 37oC (t = 2.394, df = 7, p < 0.05). The c-ELISA post challenge results showed that there was a significant difference in the reactions of the 3 groups (F = 32.21, df = 14, p < 0.05). Further analysis of the data using the tukey test indicated no significant difference between the two vaccinated groups (q = 1.151, p > 0.05). The vaccinated groups combined were however significantly different from the control unvaccinated group (q = 5.78, p < 0.05). The mean pathology scores of the animals vaccinated with the conventional and the modified T 144 vaccine were 3.4 and 3.9 respectively. The difference was not significant (t = 0.0841, df = 13, P > 0.05). The protection conferred by the two vaccines was 61.8% and 56.1% for the conventional and the modified vaccine respectively. This study recommends the continued application of the conventional vaccine in the field. Further research is also recommended to find out how the high stability of the modified vaccine demonstrated in the in vitro study can be translated in to improved vaccine efficacy