Editor’s Note: This is the first in a two-part series about Mad Cow Disease. This article examines the abnormal nature of the disease. Thursday’s article will examine the theories of how the disease transferred into the human population.

The influx of sheep to be tested for a form of Mad Cow Disease has caused concern in Ames and at Iowa State, but experts say it is unlikely the disease will appear in the United States.

New cases of bovine spongiform encephalopathy, or BSE, have been detected in several European countries, including Italy, which was previously thought to free of the disease, said Nolan Hartwig, ISU Extension veterinarian specializing in beef, dairy, sheep and veterinary public health. However, Hartwig said he thinks it is unlikely the disease will enter the United States.

“The risk of BSE getting into the United States is extremely small, extremely small,” he said, “but it’s not zero.”

BSE, or Mad Cow Disease, is a degenerative brain disease, Hartwig said. The term “spongiform” indicates that, microscopically, the nervous tissue of infected animals looks like a sponge. Hartwig compared the appearance of a brain infected with BSE to a Pac-Man game chewing and eating away at the brain. Cows infected with BSE were belligerent, uncoordinated and eventually died.

The infectious agent that causes BSE differs from most other diseases, Hartwig said. BSE is one of a family of diseases called transmissible spongiform encephalopathies. These are not caused by normal infectious agents such as bacteria or viruses, but rather by an abnormal form of a protein called a prion.

“Prions are proteins, not living organisms,” he said. “They contain no genetic material, no DNA.”

The first case of Variant Creutzfeldt-Jakob Disease, the human version of BSE, was diagnosed in England in October 1986, Hartwig said.

“In the early ’90s, we started to see some evidence of these TSEs in people in the United Kingdom,” he said.

Animals and humans infected with BSE become belligerent, uncoordinated and debilitated, Hartwig said. Since BSE is a progressive disorder, infected patients take a long time to die.

“Apparently the variant form [Variant Creutzfeldt-Jakob Disease] takes people longer to die than the traditional form,” he said.

Harley Moon, professor at the ISU Veterinary Medical Research Institute, said the idea of a protein causing an illness was controversial when first proposed by Stanley Puzner, who won a Nobel Prize for his work. Moon said this concept was a leap from previous knowledge.

“It’s not a bug,” he said. “All these other things [that cause infections] are bugs. This is not a bug – this is a protein.”

Hartwig said prion proteins are present in all animals, not just cows and other ruminants.

“We all have prions in our bodies,” he said, “but they’re formed, created and then they’re removed. It’s a natural, normal process.”

Although prion proteins are the likely cause of BSE, it is still unknown what their function is in the body, said Janice Miller, veterinary medical officer with the National Animal Disease Center of the USDA Agricultural Research Service.

“Some [scientists] think maybe it plays a role as a neurotransmitter, because it accumulates at the synaptic nerve endings,” she said.

However, she said it appears prions are not necessary for life. In some experiments, for example, the prion protein has been removed from certain strains of mice, and the mice have survived.

“We assume that there’s a good reason, but that isn’t written in stone that there has to be,” she said.

The prion that causes BSE is abnormal in the way it is folded, Moon said. He said normal prion proteins have a helical, or spiral, shape, like that of DNA, but the abnormal prions are arranged in flat, pleated sheets.

“The protein, in terms of its amino acid sequence, it’s not even a mutant protein,” he said. “It’s the normal protein sequence; it’s folded wrong.”

Due to the abnormal folding of the protein, it is unable to be broken down properly, and the protein accumulates in the nervous tissue of animals, Moon said. Current knowledge is that this accumulation is what causes BSE.

“The evidence is that this protein, by mechanisms that are not yet understood, is toxic to the brain,” he said.

The folding of the abnormal prion protein also causes other difficulties. Hartwig said the prions are very heat-resistant, so they are not “killed” or denatured by normal processes. Such heat resistance is unusual for a protein, he said.

“Usually [proteins] are like the white of an egg,” he said. “When you heat it, it denatures it. It’s just not the same, and that change is irreversible.”

Other infectious agents in meat, like salmonella or E. coli, are killed when the meat is heated to very high temperatures in the rendering process. However, prions can’t be killed in this way. Also, Moon said prion proteins appear to be resistant to other forms of decontamination such as chemical disinfectants.

“This is not a bug,” he said. “So those systems we’ve put in place to eliminate bugs don’t work here.”