A comparison of the stability, safety and efficacy of two contagious Bovine Pleuropneumonia Vaccine formulations

Abstract

A study was carried out to evaluate a modified contagious bovine pleuropneumonia (CBPP) vaccine against the standard (currently in use) vaccine. The objective was to determine whether the modified vaccine was superior to the standard one with a view to recommend for field use. Both vaccines were lyophilized preparations from the T1 vaccine strain of Mycoplasma mycoides subsp. mycoides biotype small colony (MmmSC), grown in different types of media and reconstituted in different types of diluents. The two vaccines were compared in terms of stability, safety and efficacy. To determine stability, the two vaccines were reconstituted, and then aliquoted into three parts each. One aliquot from each vaccine was then stored at +4°C, 25°C and 37°C respectively. The number of viable Mycoplasma microorganisms from each aliquot was then estimated at intervals of 0, 1, 2, 4, 8, 12, 24, 48, 72 and 168 hours using the microtitration method. The safety was determined by vaccinating two groups of randomized cattle at the tailtip, and then determining changes in tail-tip circumferences and rectal temperatures. A control group that comprised of unvaccinated animals was included. The efficacy of the two vaccines was determined by challenging the vaccinated and the non-vaccinated animals each with 60ml of a Mycoplasma broth culture containing ,3x 108 colony forming units (CFU) of MmmSC, three months post vaccination. The challenge was done using a predetermined nasotracheal intubation method aided by a bronchoscope. The challenge method had been predetermined by infecting sixteen animals each with 60ml of a Mycoplasma broth culture containing 3x 108 CFU deposited at the tracheal bifurcation using a nasotracheal bronchoscope. The efficacy of the two vaccines was compared by their protection rates which were calculated by first determining the pathology score in each animal. The pathology score was calculated using a lesion score (determined by the size and severity of the lung lesion) and a factor determined by the lesion score and whether or not Mycoplasma organisms were isolated from the lung lesion. The pathology scores were transformed into protection rates expressed as a percentage of one less the mean score of each group divided by the mean score of the control group. From the results obtained in stability studies, it was observed that there was a significant (P < 0.001) titre drop in the standard vaccine at all temperatures and at all the intervals, compared to the modified vaccine. In the safety studies, changes in tail-tip circumferences in the animals vaccinated with the standard vaccine were more severe than those vaccinated with the modified vaccine (P < 0.001), while rectal temperatures in both groups remained within the normal range. From the results obtained in the efficacy studies, there was no difference in protection rates between the two vaccines (P > 0.05). From the results of this study, it was concluded that the modified vaccine has a higher stability than the standard vaccine. Further, the modified vaccine was safer than the standard one. However, the modified vaccine was not superior to the standard vaccine in terms of efficacy. On the basis of higher stability and safety, it was therefore concluded that the modified vaccine should be recommended for field use to replace the standard one. However, further modifications

of the vaccine are needed with a view to increase the efficacy.