A serological survey forBabesiain cattle in Scotland. III. The rates of acquisition and loss of antibody toBabesiaand their effects on observed levels of antibody incidence

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Abstract
Data for age and the incidence of antibody to B. divergens in cattle from areas of high and low endemicity were analysed using 3 simple epidemiological models to estimate the rates of gain and loss of antibody. The models adequately described the observations but did not allow for an increased recovery rate attributable to acquired immunity in older animals. The rate of loss of babesial antibody in the absence of challenge was estimated directly from data for age and the incidence of antibody in Irish-bred cattle located in non-endemic areas of Scotland [UK]. These data suggested an antibody loss rate of 0.25 per annum but did not provide firm evidence for the form of the antibody loss curve. Measurements of the titer of babesial antibody supported conclusions drawn from studies of antibody incidence. In Irish-bred cattle from non-endemic areas titers declined gradually over 8-10 yr; in cattle from an area of high endemicity, titers did not change appreciably with age. Cattle tested within 1-3 mo. of infection exhibited high titers.