A strain of Pasteurella multocida associated with infections in rabbit colonies.

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 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.