Abstract
During a 3-year period strains of Group-B streptococci from 1227 (94.6 %) of a total of 1297 cases of bovine mastitis were serologically typed. Twenty-seven different antigenic combinations were found. Ab. 70 % of the strains carried polysaccharide antigens among which Type III was predominant (57 %). The protein antigen X was widespread (62 %), and 5 % of the strains were non-type able.
Type Ic predominated among “false positive” bulk milk isolates (52.2 %, 12/23), but was rarely isolated from quarter milk samples (3%).
Variation in the antigenic structure of infecting strains occurred to some extent and involved at least 10.8 % (132/1227) and probably 25.2 % (132/523) of the strains. Within a herd the antigenic variation was limited, however. Hence a definition of a herd type was possible. During the period of investigation infections caused by Herd Type III decreased numerically while the number of herds infected by other types remained almost stable.
Keywords: Group-B streptococci, serological types, bovine mastitis
Sammendrag
Serologisk typebestemmelse blev foretaget på isolater fra 95,6 % af køerne (740/774) og 94,6 % af kirtlerne (1227/1297) fra samtlige besætninger (129), hvor der i treårsperioden 1/4 1976–1/4 1979 diagnosticeredes gruppe B-streptokokmastitis (B-str. mastitis). Retypisering viste, at mindst 10,8 % (132/1227) og muligvis 25,2 % (132/523) af de inficerede B-str. stammer var antigent variable. I besœtninger, hvor fiere kirtler var inficerede (90/129), fandtes derf or hyppigst (63 %, 57/90) B-str. af mere end een „type” (Tabel 1).
Typebestemmelsesresultaterne (Tabel 2) viste, at B-str. af 28 forskellige antigenkombinationer forekom. 70 % af stammerne var i besiddelse af et polysakkaridantigen, blandt hvilke Type III var det mest udbredte (57 %). Af stammer af ren „proteintype” var der 14 % X; 11 % havde Ibc antigenet alene (8,6 %) eller sammen med X eller R. X-antigenet forekom alene og sammen med andre antigener meget udbredt (62 %); 5 % var ikke typiserbare.
Da den antigene variation blandt B-str. stammer var begrænset, kunne de 28 antigene kombinationer sammenfattes i 9 besaetningstyper (Tabel 3).
Besætningstypefordelingen blandt 100 nyinficerede besætninger (Tabel 4) viste: Type III 38 %, Ie 14 %, II 15 % og Ibc 13 %. Type Ic var det hyppigste fund (52,3 %, 12/23) blandt de „falske positive” isolater fra leverandørmaelkeprøver (Tabel 5).
Besaetningstype III syntes hurtigst at kunne sprede sig i en besaetning og især indenfor den enkelte ko (Tabel 4). Bekæmpelsesprogrammet har næsten udelukkende haft effekt overfor denne type, medens anfallet af besaetninger smittet med de forskellige øvrige typer holdt sig konstant gennem undersøgelsesperioden (Fig. 1).
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