Comparison of swine paratyphoid live vaccines lyophilized with two different stabilizers

Abstract:

[Objective] To systematically compare the physical, chemical and biological properties of the swine paratyphoid thermo-stable live vaccine (TS vaccine) and the traditional swine paratyphoid live vaccine (traditional vaccine), and provide references for evaluation of live vaccine prepared with thermo-tolerant stabilizer. [Methods] Three batches of TS vaccine and traditional vaccine were prepared. The vaccine physical properties, pureness, viable bacterial counts, safety, residual moisture, vacuity and storage period were measured according to the standard methods in Veterinary Pharmacopoeia of the People’s Republic of China. The survival ratio of the vaccines after lyophilization and the thermo-stabilities after storage at 37 °C for 7 days was compared. One batch of TS vaccine and traditional vaccine were selected for further protective efficacy study. Twenty-five piglets were randomly divided into five groups. With the exception of the non-vaccinated control, the other four groups were immunized orally (p.o.) or intramuscularly (i.m.) with 1 dose of TS or traditional vaccine. After thirty days, all piglets were challenged intravenously with 1 minimum lethal dose (MLD) of virulent Salmonella enterica serovar Choleraesuis. The protective efficacy of two vaccines were observed for 30 days post challenge. [Results] The physical properties, pureness, viable bacterial counts, safety, residual moisture and vacuity of two vaccines met the requirements of Veterinary Pharmacopoeia of the People’s Republic of China. The bacterial survival ratio after lyophilization of the TS vaccine was 88.2%, 83.1%, 86.4%, respectively, compared to the 52.3%, 56.2%, 61.4% for the traditional vaccine, respectively. After stored at 37 °C for 7 days, the survival ratio of the TS vaccine was 83.6%, 82.9%, 88.8%, respectively, compared to the 58.5%, 60.2%, 54.7% of the traditional vaccine, respectively. After stored at 37 °C for 7 days, the TS vaccine showed good properties, while the traditional vaccine had surface concave of 1/4?1/2. The storage period at 4 °C of the TS vaccine lasted 24 months, compared to the only 9 months for the traditional vaccine. The protective efficacy of the TS vaccine was 100% for oral or intramuscular immunization route. For the traditional vaccine, the protective efficacy was 100% for oral route and 80% for intramuscular route. [Conclusion] The TS vaccine had higher survival ratio after lyophilization and better thermo-stability. The TS vaccine could be stored at 4 °C for long-term and had good protective efficacy.