These conflicting reports on the efficacy of tetracyclines
for chemosterilization suggest that differences in susceptibility
between isolates may exist. This hypothesis is
supported by the recent identification of two multidrugresistant
efflux pumps in the genome of A. marginale
(Brayton et al., 2005). However, the clinical significance
or activity of these pumps has yet to be examined. If
there are indeed differences in susceptibility between
strains, it would be necessary to know which A. marginale
strain(s) are present in the herd and the efficacy of CTC
for chemosterilization of those strains. Moreover, as stated
earlier, CTC is not approved for the treatment or prevention
of bovine anaplasmosis in Canada. Clinical trials
would have to be conducted to provide data for any
approval of CTC for the chemosterilization of A. marginale
infection.