The downer dairy cow recently found stricken with mad cow disease in California was infected with an “atypical” strain. Such cases are thought to arise spontaneously, a notion the USDA seized upon to explain how the disease could arise despite their regulations. If anything, that fact highlights the weaknesses in the current feed rules. If mad cow disease can arise out of nowhere, then it’s even more important to close the loopholes and stop the feeding of cattle blood to calves and chicken manure to cows to prevent it from spreading. And what the USDA didn’t mention about the atypical strain found in California is that there’s evidence it’s a more dangerous form of the disease.

The California cow died of a particularly virulent form of mad cow disease known as BASE, bovine amyloidotic spongiform encephalopathy, also known as L-type atypical BSE. Typical BSE was first documented in the ’80s in Britain. Afflicted cows often became twitchy and aggressive, giving rise to the “mad cow disease” moniker, as their brains degenerated into a characteristic Swiss cheese-like appearance. Hence the scientific name, BSE: bovine (cow) spongiform (sponge-like) encephalopathy (brain disease).

Then cats started dying. Max, someone’s pet Siamese, was the first non-bovine victim of the disease. Infectious pet food was implicated as the cause of Max’s death from a never-before-described feline spongiform encephalopathy.

Then young people started succumbing to a human spongiform encephalopathy called Creutzfeldt-Jakob disease, a relentlessly progressive and invariably fatal dementia, often involving weekly deterioration into blindness and seizures as their brains became riddled with holes. CJD appears sporadically in one in a million people, but typically strikes only the elderly. The new cases among teenagers were dubbed “variant” CJD, a disease now understood to be caused by consuming contaminated meat (or by getting a blood transfusion from someone who did).

Despite massive contamination of the food supply, no more than a few thousand people are expected to die, suggesting a robust transmission barrier between cows and humans when it comes to BSE. The same may not be true of the atypical forms of BSE found in California and in the last two mad cows in Texas and Alabama. Experimental models of human infection suggest that the type of mad cow disease discovered in the California case “is a more virulent BSE strain… in humans,” with “higher transmissibility” and causing a swifter death.

Just as one in a million people sporadically get CJD, evidence suggests one in a million cattle get atypical BSE. The U.S. cattle population hovers around 100 million. Though there is evidence some of these sporadic human cases of CJD may be associated with infected cows or sheep, case control studies tie CJD more closely to the consumption of pork. A study co-authored by D. Carleton Gajdusek, recipient of the Nobel Prize in Medicine for his research on these diseases, found that “consumption of pork as well as its processed products (e.g., ham, scrapple) may be considered as risk factors in the development of Creutzfeldt-Jakob disease.”

Though pigs have been proven susceptible to a porcine spongiform encephalopathy, the National Pork Producers Council claims that no naturally occurring cases of “mad pig” disease have ever been discovered. The Consumers Union, publisher of Consumer Reports, however, has petitioned the federal government to reopen an investigation into a case in which a USDA veterinarian may have found a cluster of suspect pigs in upstate New York.