Mad cow disease has emerged once again in the United States, for the first time in six years. The infection was confirmed on Tuesday. A single dairy cow in California's Central Valley tested positive for a rare strain of mad cow disease, which is also known as Bovine Spongiform Encephalopathy.

Mad cow disease causes neural degeneration and can be fatal to humans who consume infected animals' nerve tissues. During 2009, an outbreak that centered in the United Kingdom killed over 150 people. This year's finding raised plenty of alarm bells, but the United States Department of Agriculture was quick to assure the public that this particular infection does not constitute a health concern.

The infected cow was put down shortly after testing positive for Bovine Spongiform Encephalopathy. Since it was a dairy cow, its beef never came close to entering the U.S. meat market. There are no concerns about its milk, as the World Health Organization confirms that mad cow disease cannot be spread by drinking the milk of an infected animal.

Scientists don't know exactly what caused this infection, but research is ongoing. A statement released by USDA Chief Veterinary Officer John Clifford suggested the California cow was a special case. Past cases of mad cow disease have been linked to the consumption of infected feed; this time, the animal was positive for atypical BSE, a very rare form of the disease not generally associated with an animal consuming infected feed.

Due to the unique nature of this infection, scientists think that this case may have occurred spontaneously and is therefore not necessarily indicative of a widespread problem.

But as health concerns were allayed, economic concerns took their place. There is a precedent for market upheaval: after a U.S. breakout of mad cow disease in 2003, the international response was nearly instantaneous. The USDA announced a presumptive positive test for Bovine Spongiform Encephalopathy just before Christmas that year, and even before a final confirmation could be made, Japan's agriculture ministry made plans to ban U.S. beef imports. Japan, which had been the top importer of U.S. beef, was followed by others including South Korea, Singapore and Taiwan.

As a result, U.S. exports of beef dropped by almost 75 percent. Months of talks and a set of strict new regulations were necessary before Japan and other countries agreed to reopen beef trade with the United States.

It's no wonder that this time around, investors got antsy at the first sign of trouble. Cattle futures fell their full 3-cent limit on Tuesday, reports Reuters. The market was already shaky due to recent concerns about pink slime, the ammonia-treated beef byproduct that was used as filler in everything from fast food to school lunches.

But on Wednesday, there was a reassuring rebound as cattle futures swung back toward stability. Big importers Japan and Mexico, calmed by restrictions in place since 2003 and reassured by the USDA's assertions of public safety, have made no move to cut down on their imports. The only setback came from South Korea, where two major retail chains refused to sell American beef products, even though South Korea itself has not imposed a ban and will continue to import from the United States.

With an essentially nonexistent health threat and minimal damage to the U.S. beef markets, this mad cow disease outbreak is amounting to little more than a minor concern. This reflects a trend of continuing success in battling Bovine Spongiform Encephalopathy; at its peak in 1992, there were 37,311 infections around the world. Last year, the number was 29. And since regulations went into effect in the United States in 1997, the California case is only the fourth cow to have tested positive for the disease.