There was only a few herds in the US with Brucellosis until recently when the buffalo came out of the park and spread it to the cattle herds - again. If you live in a state near Yellowstone Park you should especially Bangs vac. Heifers have to be done between the age of 4 and 12 months - no later is allowable. Vet needs to do this. Gives a shot, tattoo and clip. Vac is not 100% guarantee protection, but at least 65%.
If you are having abortions in your cows in late gestation this is a symptom of the brucellosis. Very contagious to cattle, buffalo, pigs and humans.
If you have had cattle come into your herd with in the last 30 days to 1 year you can see symptoms. Contracts via mucal secretions. Cow licks another cows rear or afterbirth, ect. Humans get it the same way by touching the mucus or afterbirth.
If you are selling bred cows they will be checked for tattoo - the clip will not do. Has to be a readable tattoo. Montana will not allow cattle into the state without a readable tattoo.