Call it a different kind of March Madness: Mad cow has reared its ugly head once again. A third U.S. cow has been identified as infected with brain-demolishing rogue proteins. U.S. consumers have shrugged off mad cow concerns in the past, but one might wonder how much longer that will continue if cases keep cropping up -- and if allegations continue that government agencies aren't doing enough to protect against the threat.

In humans, mad cow disease manifests as Creutzfeldt-Jakob disease, a neurodegenerative disorder contracted by eating meat contaminated with bits of infected cows' brain tissue. So far, conventional wisdom has insisted that the very minute incidence of mad cow disease in the U.S. means consumers have little to fear -- an understandable perspective at first. Although the first domestic mad cow, discovered in 2003, was Canada-born, the second diseased cow hailed from Texas. The most recent cow's birthplace is currently being investigated.

I can't help wondering how much longer U.S. consumers will feel at ease. Just as this new case was discovered, it came to light that the USDA plans to decrease mad cow testing. Its surveillance testing was hardly widespread to begin with; since 2004, the USDA has tested 652,697 of the United States' 95 million cows. Call me crazy, but given the newest case, wouldn't it be logical for the agency to increase testing instead?

As recently as January, a group of researchers joined with burger giant McDonald's (NYSE:MCD) to contend that the U.S. Food & Drug Administration's feed safeguards against mad cow disease are "inadequate." They called for more stringent guidelines on testing for the disease; McDonald's stated that there should be as close to zero risk of human exposure as possible.

Then there are protein peddlers such as Tyson (NYSE:TSN). It produces both beef and chicken, and though avian flu has not been detected in the U.S., Europe is currently in a panic over that ailment. Meanwhile, although U.S. consumers may remain nonchalant, Japan continues to ban U.S. beef. With Tyson shares struggling around 52-week lows, it might be tempting to wonder whether they have reached bargain territory. Still, there's no denying the risk of a potential storm on the horizon.

Even if U.S. consumers get nervous, steakhouses will likely prevail; unlike ground beef, where it's easier to get bits of other tissue worked into the mix, steaks and roasts have never been implicated in the disease. However, McDonald's has good reason for its concern, along with Wendy's (NYSE:WEN), Burger King, and other companies that count on Americans' appetites for the almighty burger.

(After my bull argument in a recent duel on Whole Foods Market (NASDAQ:WFMI), a Foolish reader named Rob emailed another good point to me -- that uneasiness about food safety could benefit Whole Foods and other grocers selling free-range and organic food.)

The latest mad cow case and the USDA's seemingly lax approach make me question repeated assurances from government agencies and trade associations that it's crazy to worry about mad cow disease. I certainly hope that's true, but it seems to me that mad cow is fast becoming an issue that investors should carefully consider when contemplating some of the affected companies.

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Alyce Lomax does not own shares of any of the companies mentioned.