The mad cow discovered in California last week was not really a mad cow. It suffered from a closely related disease. There is  no cause for alarm at this point, but several top scientists say the public health implications may not be as clear the U.S. Department of Agriculture would have us believe.

The diseased dairy cow from a rendering (or carcass recycling)  plant in Hanford, Calif., near Fresno, was infected with a condition variously known as BASE (bovine amyloidotic spongiform encephalopathy), atypical BSE and L-type BSE, which has so far been found in about 70 animals in the world. Lyndsay Cole, a spokeswoman for USDA, confirmed the diagnosis in an email Tuesday.

This condition, first reported in two Italian cows in 2004, causes the same rapid crippling and death as the classic bovine spongiform encephalopathy (BSE) that swept through Britain and much of Europe in the 1980s and '90s. But the brains of the animals look very different after their demise.

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Some experiments have shown that this rare disease can jump from species to species, infecting lab mice and even non-human primates. The research also suggests that the infectious agent for the rare disease could be more virulent than BSE, more likely to appear in meat (classical BSE is mostly in brain and nervous tissue) and might be carried in milk. Many scientists are quick to point out that all this research consists of studies too small to be conclusive. 

However, there is an urgent need for further study, they say.

What irks many scientists is the USDA’s April 25 statement that the rare disease is “not generally associated with an animal consuming infected feed.”

The USDA’s conclusion is a “gross oversimplification,” said Dr. Paul Brown, one of the world’s experts on this type of disease who retired recently from the National Institutes of Health.  "(The agency) has no foundation on which to base that statement.”

“We can’t say it’s not feed related,” agreed Dr. Linda Detwiler, an official with the USDA during the Clinton Administration now at Mississippi State.

In the May 1 email to me, USDA’s Cole backed off a bit. “No one knows the origins of atypical cases of BSE,” she said

The argument about feed is critical because if feed is the cause, not a spontaneous mutation, the California cow could be part of a larger outbreak.

The British and European outbreaks of BSE ignited because the industry turned cattle -- natural vegetarians -- into cannibals, feeding them the remains of cattle and other animals. U.S. farmers did the same, but Britain had a huge incidence of a related disease in sheep called scrapie, and many scientists believe that was the source of the massive cattle outbreak. Although experiments showed that BSE could infect monkeys and other animals, it was not until the first human infections that anyone realized the threat it poses to people. The human form of the disease, first discovered in Britain in the 1980s, has been blamed for the deaths of at least 280 people worldwide, with 175 in the UK alone.

How could the California cow have been infected with feed?  Following the British outbreak, ranchers in the U.S. and most of the rest of the world stopped feeding cattle the remains of cattle, sheep and other mammals. But a farmer’s feed still could get contaminated by other means. The USDA still allows chickens to consume the remains of cattle. Chicken litter, containing urine and feces, is fed to cows. That could theoretically transmit the infection to cattle.

And if it is feed, what does that say about the potential of an outbreak in the rest of this cow’s heard?  It appears the USDA and the California Department of Food and Agriculture are investigating. Dr. Jim Cullor, associate dean of the University of California, Davis, School of Veterinary Medicine and an expert on many animal illnesses, spoke to me from his office, which is close to the dairy farm that housed the sick cow.  He would not identify the farm (nor will any government agency) but he did say dairy farms in the area usually have about 3,000 animals (about half of them milk producers). But some farms in the area have as many as 10,000 head, Cullor explains. Typically, the inspectors would visit the farm’s “hospital,” where sick animals are treated. They would also go over the hospital’s records as well as the farmer’s feed and records of past feed purchases. 

“That farmer will feel like he’s had a visit from the IRS,” Cullor quipped.

But does such an inspection guarantee safety? Dr. Michael Hansen of the Consumers Union, along with many scientists, argues that, like Europe, the U.S. should test all animals that look sick or are over 6-years-old before they enter the food supply. The rationale behind testing healthy animals 6 years old or older is that BSE usually takes that long to develop. 

"With thorough testing we would know the food supply is safe,” Hansen said. “We wouldn’t be guessing.” 

We would also learn the true incidence and origin of spontaneous and atypical cases.

But the U.S. tests far fewer animals -- about 40,000 of the 35 million cattle slaughtered annually. The argument is about cost, an estimated $25 to $30 per animal.  Widespread testing would add a few cents to the cost of a pound of beef. Britain, Europe, Japan and several other nations have decided it is worth it. The USDA says it is not and declares: “The surveillance program allows USDA to detect the disease if it exists at very low levels in the U.S. cattle population.”

Few scientists would argue that the one California cow which never was headed to the U.S. food supply represents a health hazard. But many maintain that the current surveillance is insufficient. Dr. Kurt Giles, an expert in neurogenerative diseases now at the University of California, San Francisco, was at Oxford during the British outbreak.  He told me USDA’s assurances about safety today remind him of British statements during the 1980s. 

“It is so reminiscent of that absolute certainty,” he said.

Robert Bazell is NBC's chief science and medical correspondent. Follow him on Facebook and on Twitter @RobertBazellNBC

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