L. L. Callow

Reduction in virulence of Babesia bovis due to rapid passage in splenectomized cattle

Abstract A marked loss of virulence of Babesia bovis for normal cattle was observed during its rapid serial, blood passage in splenectomized calves. In 2 strains studied closely, responses to infection in cattle inoculated with parasites collected from the 11th passages were minimal, although the splenectomized donors were severely affected. The change was reversed by passaging in intact hosts, and in one experiment the parasites had become very virulent at passage 5. The finding has proved useful in the preparation of safe, living vaccines to control babesiosis. Selection either for immunogenic antigens, against immunosuppressive ones, or a combination of these effects may cause the decrease in virulence.

Development of a solid-phase radioimmunoassay for antibody to antigens of Babesia bovis infected bovine erythrocytes

Abstract Kahl L. P. , Anders R. F. , Callow L. L. , Rodwell B. J. and Mitchell G. F. 1982. Development of a solid-phase radioimmunoassay for antibody to antigens of Babesia bovis infected bovine erythrocytes. International Journal for Parasitology 12 : 103–109. A quantitative solid-phase radioimmunoassay (RIA) has been developed for the purpose of ranking sera from exposed animals according to their titre of anti- B. bovis antibody. The antigen was a sonicate of lysed infected blood cells, and antibody binding was detected with 125 I-labelled anti-bovine IgG. The assay was tested using sera from experimentally infected splenectomized and intact cattle and from animals resident in an endemic area. A high specificity for B. bovis was demonstrated. There was good agreement in identifying exposed cattle when the test was compared with an indirect fluorescent antibody (IFA) test although no correlation was seen between titres obtained in the two tests. Analysis of the effects of challenge infection with B. bovis on IFA and RIA titres in previously exposed animals illustrated that the RIA was a more sensitive test for detecting changes in antibody titre.