Sorry I meant antibodies to antigens not simply antigens The sera of most vets in the USA contains antibodies to dog brucellosis and about  of men and  or women do likewise in the USA This would suggest far more animals carry the bacterium than we would think Now the presence of antibodies means exposure not necessarily infection Infection depends on many things including the genetic makeup of the person being exposed hisher health at the time but mostly on the degree of exposure was it one bacterium that landed in the mouth from an aerosol or was it billions of bacteria that sat in the vagina for hours etc If this topic interests you follow it up with this study