EXPERIMENTAL-INFECTION OF CATTLE WITH SEVERAL BORRELIA-BURGDORFERI-SENSU-LATO STRAINS - IMMUNOLOGICAL HETEROGENEITY OF STRAINS AS REVEALED IN SEROLOGICAL TESTS

Twenty-three experimental cattle, mainly calves, were each inoculated 1-3 times with one of ten Finnish Borrelia burgdorferi sensu late stra ins. All three genospecies were represented. Borreliae were administer ed mainly by both intravenous (about 10(6) to 10(9) spirochaetes) and intradermal (10(4)) routes, and on six occasions subcutaneously (10(3) ) only. For infectivity control and comparison purposes mice and rabbi ts were inoculated simultaneously. Immune responses in cattle were mon itored both with whole-cell sonicate enzyme-linked immunosorbent assay (IgG-ELISA) and indirect immunofluorescent assay (IgM-IgG-IFA). Five Finnish strains and the American strain B31 were used as antigens. No clinical signs of borreliosis were observed. Of the strains, 7/10 were interpreted by the immune responses to have caused relatively short-t erm subclinical infections of varying intensity. Borreliae could not b e isolated from blood or other organ specimens of cattle. A rough esti mate of the mean infectious dose in the conditions of experiments is 1 0(6) to 10(7) organisms. In conclusion, the overall result appears to argue a low susceptibility of cattle to clinical borreliosis, at least when infected by Finnish strains of the agent. Significant antigen-sp ecific differences were observed both by ELISA and LFA in detection an d quantification of immune responses. As a rule, the homologous antige n was found to be the most sensitive. Genospecies differences were mos tly distinct. Antigens of two Borrelia garinii isolates proved practic ally equal in sensitivity, whereas major differences were displayed be tween two Borrelia afzelii antigens. In an IFA study, an American (B31 ) and a Finnish B. burgdorferi sensu stricto strain proved equally sen sitive as antigens. In two relatively strong primary immune responses the antigen-specific measurement differences were such that diagnostic ally in a cross-sectional study only the homologous antigen or an anti gen of the same genospecies would have been sufficiently sensitive to show a positive result. (C) 1998 Elsevier Science B.V.