Mad Cow Disease - How Do We Know We're NOT At Risk? Reader Questions Answered.
As a follow-up to our previous post on the California dairy cow with “mad cow disease”/BSE, there were a few reader questions. We talked to Dr. James Roth, from Iowa State University, to provide some clarity.
- Director of the Center for Food Security and Public Health
- Distinguished Professor of Vet Microbiology & Preventive Medicine at Iowa State University
Question from Best Food Facts reader, Denise: We learned before that BSE is not contagious. If this is the case, how do cattle contract the disease?
Dr. Roth: "Cattle can contract BSE in one of two ways:
1. "Consumption of BSE-contaminated bovine products: The brain and spinal cord are the products that carry BSE. These bovine products were banned from the food supply in 1997.
2. "Spontaneous rare mutation: It’s rare, but possible. BSE is a prion (an infectious agent made of protein) that can cause confusion in the body where the prion becomes stable and other healthy proteins mutate and match it. This leads to mass infection, dementia and ultimately death.
"Other than the 2003 case of a U.S. cow with BSE, which was a cow born in Canada prior to the feed ban, the instances of BSE here have been of the spontaneous nature. We do know that it is rare, but it will continue to happen because of the nature of the disease. In the most recent case of BSE in a California dairy cow, spontaneous mutation was found to be the cause."
Question from Best Food Facts reader, Mujahid: How can it be said that there are no other cows with this disease?
Dr. Roth: "Well, we can’t say that. In fact, it is actually likely that more cases will show up every few years. It’s possible (as it always has been) that a rare case like this could come up. It always shows up later in the life of the animal.
"Because it takes years to manifest, most cattle in feedlots aren’t old enough to develop the disease. Once it is developed fully, the cattle are immobile or have other clinical signs, so they can’t go to slaughter.
"It would be very rare, but some cattle could go to slaughter before any clinical signs, which means there wouldn’t be much prion in the brain. To protect against this, though, slaughter protocols have changed so as to remove specified risk material to protect humans, and they removed the potential for feeding animal products to protect cattle."
Best Food Facts: What are the signs of BSE in cattle?
Dr. Roth: "Cattle affected by BSE experience progressive degeneration of the nervous system. Affected animals may display changes in temperament (nervousness or aggression), abnormal posture, lack of coordination, difficulty in standing up, decreased milk production, or weight-loss without noticeable loss of appetite. There is no treatment nor a vaccine to prevent the disease. The disease’s incubation period is from two to eight years, and following the onset of clinical signs, the animal’s condition deteriorates. This process usually takes from two weeks to six months."
Best Food Facts: What is being done to protect animal health?
Dr. Roth: "The primary animal-health protective measure is a feed ban. In 1997, the FDA implemented regulations that prohibit the feeding of most mammalian proteins to ruminants, including cattle. This feed ban is the most important measure to prevent the transmission of the disease to cattle. The feed ban was strengthened in 2008, by additional prohibitions on those tissues that have the highest risk of transmitting BSE. These additions to the feed ban prohibit the use of brain and spinal cord from cattle 30 months of age and older for use in any animal feed."
Best Food Facts: Is cow’s milk a source of BSE?
Dr. Roth: "No. Scientific research indicates that BSE cannot be transmitted in cow’s milk, even if the milk comes from a cow with BSE. The same is true for beef."
Best Food Facts: So, are milk and milk products BSE-safe?
Dr. Roth: "Yes. The World Health Organization (WHO) has stated that tests on milk from BSE-infected animals have not shown any BSE infectivity. Milk and milk products are, therefore, considered safe."
Best Food Facts: Is there any ongoing monitoring taking place to ensure BSE is a non-issue for consumers? If so, what is being done to tackle the risk of BSE cases entering the food chain?
Dr. Roth: "USDA’s Food Safety Inspection Service (FSIS) is monitoring BSE. Because it’s so rare, the testing is targeted on the highest risk animals. In terms of our medical care, it’s similar to human screening for rare diseases. We don’t test every person for the disease; instead, we focus on those with related symptoms and those who are at the highest risk. If we were to test every animal – just as if we were to test every human – we would likely see instances of false positives, as is common with cancer screenings.
"The evidence that it’s working is that we haven’t had a case in humans that originated from the U.S. So, what’s in place is working very well."
Best Food Facts : How does USDA conduct surveillance for BSE in the U.S.?
Dr. Roth: "USDA has an ongoing, comprehensive, interagency surveillance program to detect signs of BSE in the United States. USDA’s BSE surveillance program samples approximately 40,000 animals each year and targets cattle populations where the disease is most likely to be found. The targeted population focuses on cattle exhibiting signs of central nervous disorders or any other signs that may be associated with BSE, including emaciation or injury, and dead cattle, as well as non-ambulatory animals.
"Samples from targeted populations are taken at farms, veterinary diagnostic laboratories, public health laboratories, slaughter facilities, veterinary clinics, and livestock markets. About 5,000 samples are also collected each year from renderers and similar salvage facilities.
"USDA’s National Veterinary Services Laboratories in Ames, IA at Iowa State University, along with contracted veterinary diagnostic laboratories, use rapid screening tests as the initial screening method on all samples. Any inconclusive samples are sent to NVSL for further testing and analysis."