Efforts to rid the U.S. cow population of tuberculosis have been underway since 1917, when scientists developed the first accurate early detection test. After nearly a century of increasingly more diligent scrutiny and culling programs, total eradication remains elusive.

Six new infected animals have been identified in recent months by animal health officials in Colorado and Kentucky – a seemingly inconsequential number, but an extremely serious reminder that more work remains to be done.

In late May, a Pennsylvania slaughter plant identified a single beef cow as being infected. A subsequent test of its entire herd in northern Kentucky found one additional positive animal. Both were slaughtered and neither entered the human food supply. Kentucky has been certified TB-free by the U.S. Department of Agriculture since 1987. It will remain so as long as another TB-infected animal is not found during the next six months.

In late June, a dairy cow in southern Colorado was identified when she went to slaughter. Subsequent testing of her entire 500-cow herd found three more positive animals. All were slaughtered and none of the meat entered the human food supply. All milk that is sold commercially is pasteurized, which kills the TB bacteria.

Eradication of infected animals and pasteurization of milk are two of the key steps taken by state and federal health officials to protect human health from tuberculosis. Prior to their adoption, TB ranked as one of the leading causes of death in the U.S.

As of July 1 a total of 46 states were certified TB-free. The only exceptions were California, Michigan, Minnesota, and New Mexico. TB is naturally present in deer, elk, bison and other wild animal populations, and is perhaps the biggest obstacle to its total eradication.