Classic bovine spongiform encephalopathy (BSE), sometimes called "mad cow disease," has been a major concern around the world since it was first diagnosed in cattle in the UK in the late 1980s. At its peak in the early 1990s, tens of thousands of cattle, particularly in the UK were diagnosed, causing a worldwide scare.
When the BSE epidemic reached its peak, cases were occurring at a rapid rate. But as more information became available and scientists implemented aggressive prevention and control measures, the rate of disease onset has slowed dramatically.
In April, USDA confirmed the nation’s fourth BSE case. A dairy cow in California tested positive for atypical BSE. It was tested at a rendering plant in central California and was never presented for slaughter for human consumption; so it did not present a risk to the food and milk supply, or to human health in the U.S.
Atypical BSE is a very rare form of the disease that is believed to be spontaneous and not associated with an animal consuming contaminated feed. The cow in this case was more than 10 years old, putting it in a higher risk category for the disease. USDA has since quarantined two dairies that were associated with the BSE case and found no link between the food the animal consumed and the disease, suggesting the case did, in fact, occur randomly. Those quarantines have now been lifted.
Classic BSE and atypical BSE are two different forms of the disease in cattle. Classic BSE usually occurs in cattle from three to five years old with clinical signs typically including hyper-sensitivity and hyper-reactivity to stimuli. Cattle with atypical forms manifest mental dullness and generally occur in animals over eight years old. Interestingly, atypical forms of BSE tend to be found in older cattle and have been found in countries considered to be at low risk for BSE. These findings suggest atypical BSE forms are sporadic in nature.
While any case of BSE is a concern, consumers – and the food processing industry -- should feel confident that the U.S. food supply is safe. In fact, this case further proves that the U.S. BSE surveillance system is working.
The U.S. cattle herd is more than 90 million head, and more than 30 million head are processed annually. Since 2003, the U.S. has diagnosed four total cases of BSE. Of the four cases, only the first case in 2003, a cow from Canada, was diagnosed with classic BSE. The recent case is the first since 2006 and, like the previous two cases, all the cattle were diagnosed with atypical BSE. The bottom line is that translates into one of the lowest rates of BSE in any nation that has ever diagnosed a case.
Also reassuring is the fact that no case of the human version (called Variant Creutzfeldt-Jakob Disease or vCJD) has ever been associated with U.S. beef consumption. In the UK, where nearly all of the human cases occurred, it was common to consume parts of the animal that can transmit the disease, like the brain of older animals. That was never a common practice in the U.S., and since 2004 it has been illegal. The U.S. learned from the British experience with the disease, and we were able to translate our learnings into strong, proactive interlocking safeguards that have served us well.
The U.S. approach has been one of prevention, using a "multiple firewalls" strategy. These firewalls prevent BSE from being introduced into the U.S. and would quickly control its amplification and spread to animals and humans. Key firewalls include:
- Ban the import of cattle and beef products from countries with BSE.
- Aggressive surveillance -- Since 2004, USDA has tested more than 800,000 cattle that are most at risk.
- Controlling what cattle are fed -- The feeding of protein derived from ruminant animals (cow, sheep, goat or deer) to ruminants has been banned since 1997.
- The removal of specified risk materials (SRM). SRMs are skull, brain, trigeminal ganglia, eyes, vertebrae, spinal cord and the dorsal root ganglia from cattle 30 months of age and older.
And small intestine and tonsils from cattle of all ages.
Additional firewalls include a ban on non-ambulatory cattle from food supply and the prevention of carcasses that are tested for BSE from entering the food supply until a negative result is achieved.
Atypical BSE is sporadic, occurring a randomly in some cows, and more research is being done to determine exactly what causes this infrequent finding, how early it can be detected and whether it can be prevented. These cases, while important to track, are not indications of an increased threat.
Our surveillance system is designed to find cases when they occur with a high degree of certainty, and we remove the parts of the animal that could pose a risk. Worldwide, BSE cases have dropped from tens of thousands per year in the 1990s to 29 around the world in 2011. Prevention practices and surveillance systems are working and people should feel confident in the health of our cattle supply and the safety of our beef.