Protection, humoral and cell-mediated immune responses in calves immunized with multiple emulsion haemorrhagic septicaemia vaccine.

A multiple emulsion (ME), vaccine against Pasteurella multocida (P52) infection in cattle was prepared and the efficiency in terms of immunity to direct challenge, duration of this immunity for up to 1 year and the role of humoral and cell-mediated immune mechanisms were studied. ME vaccine was sterile, safe and was potent when tested in rabbits and calves. Nineteen calves were immunized with a single 4 ml dose of ME vaccine intramuscularly. Group of these calves were challenge infected with virulent P. multocida (P52) (10(-1) 18 h old broth culture) given by the subcutaneous route at 21 days, 3 months, 6 months, 9 months and 1 year. All the immunized calves withstood challenge infection and showed 100% protection. Humoral immune response was measured by indirect haemagglutination test (IHA) and enzyme-linked immunosorbant assay (ELISA). Statistically ELISA values were found to be superior to IHA values because of small coefficient of variance. A fall in mean antibody titres during 24 h, 48 h, post-challenge infection was recorded whereas a steady increase in the titre after 72 h up to 10 days was noticed. The prechallenge mean titre in animals correlated with survival of animals. Humoral antibodies were detected as early as 7 day post-immunization and persisted to 1 year after immunization. Leucocyte migration inhibition test showed > 20% migration inhibition during all pre- and post-challenge periods in animals suggesting an involvement of cell-mediated immune mechanism in protection. Our findings suggested that both humoral and cell-mediated immune responses contribute to protection in vaccinated animals. The results of these studies of ME vaccine showed that it can be successfully used for the effective control of haemorrhagic septicaemia.