Effect of storage on the prevalent alum-precipitated hemorrhagic septicaemia vaccine in Pakistan and preparation of a more efficient oil adjuvant vaccine using dense culture of Pasteurella multocida Roberts type 1 on an improved culture medium.

Significantly drastic effects of storage on the potency of the alum-precipitated haemorrhagic septicaemia (APHS) vaccine are reported. The APHS vaccine, studied through challenge infection of vaccinated rabbits (post-60 days of vaccination), showed 100% potency when stored at 4 degrees C for 30 days. The potency dropped to 20% when storage period was extended to 60 or more days. At 30 degrees C, the potency reduced by 40, 40 and 60%, respectively, after 30, 60 and 90 days of storage, while, at 37 degrees C, the decrease was 60, 60 and 100% after 30, 60 and 90 days of storage, respectively. In view of this, the oil-adjuvant (OA) HS vaccine was developed by culturing Pasteurella multocida on a medium comprising yeast extract, sucrose, trypticase and sodium bicarbonate, under continuous aeration at 37 degrees C. This gave a far better bacterial count (maximum count 15 x 10(8)/ml) than the conventional APHS vaccine (maximum count 6 x 10(8)/ml). The OAHS vaccine-carrying water-in-oil emulsion remained stable at room temperature for 1 year. The log protection values of the two batches of the OAHS vaccine, studied in mice, were 5.2 and 5.3, as against 1.9 of the APHS vaccine.