Abstract:
A two-year field study was conducted in four communal grazing areas in South Africa. Sera were
collected from young cattle (6-18 months old) in these areas during the winters of 1991 to 1993. The
sera were tested for antibodies to Babesia bovis, Babesia bigemina, Anaplasma marginale and Cowdria
ruminantium. In two of the four areas, treatment with acaricide was erratic and dependent on the
discretion of individual owners. In these areas the drought of 1992 had a major impact on tick burdens
and there were changes in the seroprevalence to tick-borne diseases. In the other two areas
there was a reduction in the intensity of acaricide application and this was associated with an increase
in seropositivity to the tick-borne diseases. Increases in the prevalence of seropositivity and the presence
of endemic instability, as calculated from inoculation rates, were not accompanied by outbreaks
of clinical disease. Possible reasons for this are discussed.
