Comparison of alum-absorbed or non-alum-absorbed oil emulsion vaccines containing either pilate or non-pilate Bacteroides nodosus cells in inducing and maintaining resistance of sheep to experimental foot rot
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Abstract
Highly pilate (P) or non-pilate (NP) cells of Bacteroides nodosus were compounded
into oil emulsion (O) either with or without prior absorption onto alum (A). The abilities
of these four preparations (referred to as PAO, NPAO, PO and NPO vaccines) to stimulate
antibody production and to protect sheep from foot rot were compared. Two injections
of PAO vaccine protected sheep against homologous challenge 12 weeks after the second
dose by PO, NPO and NPAO vaccines were less effective. Sheep were protected against
homologous challenge for 14 weeks after a single dose of PAO vaccine and for 22 weeks
after three doses; an ameliorative effect was still evident 40 weeks after the third
dose. Protection against challenge with two heterologous strains was demonstrated
at six weeks after three doses of vaccine. A numerical system of scoring the lesions
also confirmed that foot rot in vaccinated sheep challenged outside the 'protective'
period of the vaccine was somewhat less severe than in controls. PAO vaccine induced
much higher and more persistent titres of agglutinins than the other vaccines tested.
There was a relationship between agglutinin titres and resistance to homologous challenge.