An Evaluation of the Thermotolerance of Various Formulations of Freeze-Dried and Reconstituted Peste des Petits Ruminant Vaccines

Abstract

Peste des Petits Ruminants (PPR) disease is widely distributed in Africa. Live attenuated PPR vaccines are produced using approved Nigeria 75/1 and Sungri/96 strains by the World Organisation of Animal Health (WOAH) to control the disease. These PPR vaccines are very efficacious; however, the main challenge is the maintaining of the cold chain during vaccine distribution and delivery. This study evaluated the thermotolerance of freeze-dried and reconstituted PPR Nigeria 75/1 vaccines from vaccine manufacturers using eight stabilizer formulations (lactalbumin hydrolysate and sucrose, sucrose and peptone, Weybridge medium, trehalose, Lactose and N-Z Amine, lactalbumin hydrolysate, sucrose and L glutamine, skimmed milk, and lactalbumin hydrolysate, maltose and gelatine). Aliquots of the reconstituted PPR vaccine batches were titrated after 2, 4, and 6 h of storage at 4 °C and 40 °C. The PPR vaccines were also titrated after storage at 40 °C and 45 °C for 3 and 5 days. The results showed that reconstituted PPR vaccine stabilized with lactalbumin hydrolysate-sucrose promoted tolerance at 40 °C for 6 h. It was also noted that all reconstituted PPR vaccine formulations except the formulation stabilized with lactalbumin hydrolysate-maltose-gelatine maintained the titre above a 10^2.5 TCID₅₀/dose after 4 h of storage at 4 °C. Furthermore, the results showed that the PPR vaccine formulation containing lactalbumin hydrolysate sucrose was as the only one that maintained the titres above 10^2.5 TCID₅₀/dose after storage at 45 °C for 5 days, with a titre loss of 10^0.95 TCID₅₀/dose. Therefore, vaccine manufacturers producing PPR vaccines for use in tropical field regions could preferably use lactalbumin hydrolysate-sucrose stabilizer in vaccine formulation.

Keywords: peste des petits ruminants vaccine; stabilizers; thermotolerance.

Figure 1

Titres of PPR freeze-dried vaccines after storage at 40 °C for 3 and 5 days. All PPR vaccines had titres above 10^2.5 TCID₅₀/dose at day 0. PPR vaccines (2, 5, 6) had minimum required titre of 10^2.5 TCID₅₀/dose after storage at 40 °C for 3 and 5 days while PPR vaccines (1, 3, 4, 7, 8, 9, and 10) had titres below 10^2.5 TCID₅₀/dose after storage at 40 °C for 3 and 5 days.

Figure 2

Titres of PPR freeze-dried vaccines after at storage at 45 °C for 3 and 5 days. All PPR vaccines had titres above 10^2.5 TCID₅₀/dose at day 0. Only PPR vaccine 2 maintained minimum required titre of 10^2.5 TCID₅₀/dose after storage at 45 °C for days 3 and 5. However, PPR vaccines 1, 3, 4, 5, 6, 7, 8, 9, and 10) had titres below 10^2.5 TCID₅₀/dose after storage at 45 °C for 3 and 5 days.

Figure 3

Titres of reconstituted PPR vaccines after storage at 4 °C for 2, 4, and 6 h. PPR vaccines 1 to 10 had titres above 10^2.5 TCID₅₀/dose at 0 h. PPR vaccines (1, 2, 3, 5, and 6) maintained titres above 10^2.5 TCID₅₀/dose up to 6 h. PPR vaccines (4, 7, 8, and 9) maintained titre of 10^2.5 TCID₅₀/dose up to 4 h. PPR vaccine 10 maintained titre of 10^2.5 TCID₅₀/dose only up to 2 h of storage.

Figure 4

Titres of PPR reconstituted vaccines after storage at 40 °C for 2, 4, and 6 h. All PPR vaccines had titres above 10^2.5 TCID₅₀/dose at 0 h. PPR vaccines 2 and 3 maintained titre above 10^2.5 TCID₅₀/dose up to 6 h of incubation. PPR vaccines 1, 4, and 6 had titres above 10^2.5 TCID₅₀/dose up to 4 h of incubation. PPR vaccines 7, 8, 9, and 10 could not maintain minimum titre of 10^2.5 TCID₅₀/dose after storage at 40 °C for 2, 4, and 6 h.

Figure 5

The performance of PPR vaccine control (TCID₅₀). The titres from control runs 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and 14 to 24 had the minimum required titre of 10^2.5 TCID₅₀/dose. An exception was seen with control run 13, with the titre slightly below 10^2.5 TCID₅₀/dose.