Abstract
Pasteurella multocida was isolated from 4 conventional rabbit colonies. Amongst 51 isolates, 48 (94%) belonged to a group of strains with similar morphological, cultural, biochemical and antigenic characteristics; they were named for convenience Lo strains and gave rise to local or ascending infections. All Lo strains were found to be a new serotype, but 8 of them had additional antigenic factors characteristic of known serotypes.
The other 3 isolates (6%) were identified as serotype 3, known to have a wide host range: 2 strains were associated with septicaemia and haemotogenic spread, and 1 with snuffles.
Diagnostic agglutinating antibodies were present in the sera of adult rabbits. Maternal antibodies were in the sera of rabbits of 3 and 4 weeks old, but by the age of 8 weeks the titres had fallen to an undetectable level.