The aims of this study were to identify the prevalance and distribution of
Pasteurella haemolytica serotypes causing pneumonic pasteurellosis in sheep and goats
in Malaysia, assess the efficacy of a novel P'. haemolytica vaccine in field trials and to
isolate, characterise and assess the immunological significance of the polysaccharide
capsule of P. haemolytica A2. The serotyping study indicated that there was little
difference in the relative frequency of occurrence of A serotypes in the UK and in
Malaysia. Serotype A2 was by far the most common and the other A serotypes did not
differ significantly in order of prevalence. However, T biotypes appeared to be very rare
in Malaysia compared to UK. When electrophoretic protein and lipopopolysaccharide
profiles of some common strains from both countries were compared there appeared to
be no significant differences among the strains. Four to five major protein bands with
about twenty minor bands were shown to be present. The lipopolysaccharides profiles
were of rough-type.
A new P. luicnio/viiid iron-regulated protein (IRP) vaccine was tested in field
studies for its efficacy in preventing pasleurellosis in Malaysian sheep farms. The results
showed that this vaccine generated an immune response as measured in LLISA and IIIA
tests. I he antibody liters were significantly higher in the vaccinated sheep and there
appeared to be protection against clinical pasleurellosis following vaccination.
The capsular polysaccharide antigen of P. haemolytica A2 was identified as an
important immunogen and as a candidate for a future Pasteurella vaccine. An outer
membrane protein-polysaccharide (OMP-PS) complex was successfully prepared from an
ovine isolate of P. haemolytica serotype A2 by precipitation from log phase culture
supernatant and subsequent purification by column chromatography. The optimum
production of the complex was determined to be in 6 hour culture and comprised protein
and polysaccharide (4.1 w/w) with low in lipopolysaccharide content.
This complex was immunogenic in mice and adult sheep with induction of
humoral anti capsular antibody in indirect heamagglulination (IHA) test and anti-OMP
antibodies in immunoblolting. Direct immunisation of mice with the complex vaccine
demonstrated significant protection against A2 infection. The sera from two-year old
sheep immunised with OMP-PS passively protected mice against A2 challenge. Three month old lambs immunised with the same vaccine did not respond serologically and this
sera did not passively protect mice.
In vitro studies using ovine and murine macrophages indicated that the mechanism
of protection is antibody mediated phagocytosis as the opsonophagocytic activity of
immune sera could be demonstrated. These results indicate the potential of a /' .
hitemolytica A2 OMP-PS complex vaccine to immunise adult sheep and suggests that
passive protection of lambs against A2 infection is obtainable.