Study of babesiosis and anaplasmosis in relation to tick burdens of dairy calves in the eastern Bolivian lowlands.
The aim of this paper was to study the relationship between tick burdens and inoculation rates for Babesia bovis, B. bigemina and Anaplasma marginale in dairy farms in Santa Cruz, situated in the tropical eastern lowlands of Bolivia. In these farms, cattle are periodically dipped with acaricide against the cattle tick Boophilus microplus, the only species of significant importance in this region. 51 Holstein calves from 4 dairy farms were selected between April and September 1998. Animals were visited monthly from the age of 2-3 months until they were 7-8 months old. Monthly standard female tick counts were carried out, and serum samples were taken from them. Samples were tested for antibodies against B. bovis, B. bigemina and A. marginale using indirect ELISA. These results served to calculate inoculation rates for each of the haemoparasites. A significant linear correlation was found between log-transformed tick numbers and inoculation rates for B. bovis, but not for B. bigemina and A. marginale. A theoretical minimum number of ticks necessary for endemic stability was calculated from regression formulae.