PROTECTION, HUMORAL AND CELL-MEDIATED IMMUNE-RESPONSES IN CALVES IMMUNIZED WITH MULTIPLE EMULSION HEMORRHAGIC SEPTICEMIA VACCINE

A multiple emulsion (ME), vaccine against Pasteurella multocida (P52) infection in cattle was prepared and the efficiency in terms of immuni ty to direct challenge, duration of this immunity for up to I 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 an d calves, Nineteen calves were immunized with a single 4 mi dose of ME vaccine intramuscularly.? Group of these calves were challenge infect ed with virulent P, multocida (P52) (10(-1) 18 h old broth culture) gi ven by the subcutaneous route at 21 days, 3 months 6 months, 9 months and I year All the immunized calves withstood challenge infection and showed 100% protection, Humoral immune response was measured by indire ct haemagglutination test (IHA) and enzyme-linked immunosorbant assay (ELISA). Statistically ELISA values were Sound to be superior to IHA v alues because of small coefficient of variance, A fall in mean antibod y titres during 24 h, 48 h post-challenge infection was recorded where as 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 a nimals, Humoral antibodies were detected as early as 7 day post-immuni zation 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-me diated immune mechanism in protection, Our findings suggested that bot h humoral and cell-mediated immune responses contribute to protection in vaccinated animals, The results of these studies of ME vaccine show ed that it can be successfully used for the effective control of haemo rrhagic septicaemia. (C) 1997 Elsevier Science Ltd.