EFFICACY OF PASTEURELLA-HAEMOLYTICA SUBUNIT ANTIGENS IN A GOAT MODEL OF PASTEURELLOSIS

The effectiveness of Pasteurella haemolytica biovar A, serovar 1 (Ph 1 ) subunit vaccines was tested in goats, using challenge exposure by tr ansthoracic injection. Twenty-two weanling male Spanish goats were ran domly allotted to 4 groups. Six goats were given 2 transthoracic injec tions into the lung 18 days apart with live Ph1 impregnated in agar be ads (positive controls). Six goats were not given injections (negative controls). Five goats were given 2 transthoracic injections into the lung 18 days apart with 4.6 mg of cytotoxin in agar beads. The remaini ng 5 goats were given 2 IM injections, 18 days apart, into the thigh w ith 4.6 mg of cytotoxin emulsified in incomplete Freunds' adjuvant. Tw enty-four days after the second injection, all goats were challenge-ex posed to live Ph1 by transthoracic injection into the lung, and 4 days later, all goats were euthanatized and necropsied. Serum neutralizing anticytotoxin titer was measured throughout the experiment. Mean volu me of consolidated lung tissue was 0.38 cm3 for the positive control g roup, 32 CM3 for the negative control group; 19 CM3 for the cytotoxin- lung group; and 88 CM3 for the cytotoxin-adjuvant-IM group. Only the p ositive control group was protected from Ph1 challenge exposure. The P h1 cytotoxin subunit vaccine alone appeared to be ineffective, and the anticytotoxin titer was not correlated with protection. In a separate trial, 32 weanling male Spanish goats were randomly allotted to 5 gro ups. Each was given 2 transthoracic injections into the lung 22 days a part. Six goats were given Ph1 cytotoxin impregnated into agar beads; 6 were given Ph1 lipopolysaccharide impregnated in agar beads; 6 were given Ph1 capsule impregnated in agar beads. Six goats were given agar beads only (negative controls), and 6 were given live Ph1 impregnated into agar beads (positive controls). Twenty days after the second inj ection, all goats were challenge-exposed to live Ph1 by transthoracic injection into the lung, and 4 days later, all goats were euthanatized and necropsied. Mean volume of consolidated lung tissue was 0.14 cm3 for the positive control group, 7.59 cm3 for the negative control grou p, 11.21 cm3 for the cytotoxin group, 10.19 cm3 for the lipopolysaccha ride group, and 1.6 cm3 for the capsule group. Again, only injection o f live Ph1 (positive controls) induced solid protection; however, the capsule subunit vaccine induced partial protection against challenge e xposure in this trial. Lipopolysaccharide and cytotoxin subunit vaccin es were ineffective in protecting goats against challenge exposure wit h live Ph1.