EVALUATION OF 3 EXPERIMENTAL SUBUNIT VACCINES AGAINST PNEUMONIC PASTEURELLOSIS IN CATTLE

The objective of this study was to evaluate the efficacy of three Past eurella haemolytica A1 derived experimental subunit vaccines against p neumonic pasteurellosis in cattle, The three vaccines were: (a) cultur e supernatant (CS) containing leukotoxin (Lkt), lipopolysaccharide (LP S) and capsular polysaccharide (CP), (b) sodium salicylate extract (SS E) containing iron regulated outer membrane proteins (IROMPs), LPS and CP, (c) and a combination of the above two. Vaccine efficacy was defi ned in terms of reduction in clinical and pneumonic lesion scores afte r intrapulmonic challenge with live P. haemolytica. The results indica te that the CS vaccine elicited antibodies against both Lkt and CP, wh ile the SSE vaccine elicited antibodies against IROMPs and CP. Animals inoculated with the combination vaccine showed increased levels of an tibodies against IROMPs, Lkt and CP. There was significant correlation between lung and serum antibodies against Lkt, CP and IROMPs. Animals that received the combination vaccine had significantly lower mean pn eumonic lung score as compared to SSE and control groups. The animals which received CS vaccine had mean pneumonic lung score significantly lower than that of control group. A strong negative correlation existe d between serum antibody levels against Lkt, IROMPs, CP and pneumonic lung scores. The results from this study demonstrate the usefulness of CS vaccine alone or in combination with SSE vaccine in bringing about optimal protection in vaccinated calves, against experimental pneumon ic pasteurellosis.