Horizontal transmission in sheep and delayed clearance in guinea pigs and mice of a Brucella melitensis Rev. I mutant.

Virulence assays in guinea-pigs, mice and sheep with a Rev. I mutant strain (FSA) demonstrated that the latter had increased virulence in comparison with a reference strain. The mutant showed slower clearance in guinea-pigs and mice when compared with standard Rev. I strains and horizontal transmission was achieved in 2 sheep.