Genetically altered prion-free cattle may be solution to mad cow disease

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SALEM, Ohio – Cattle, fingered for dozens of cases of the disease infamously dubbed “mad cow” around the globe, may prove to be not just the carrier, but also a solution to the disease.
Late in December came reports that USDA and Hematech, a South Dakota-based pharmaceutical research company, had bred genetically modified cattle that do not produce prions.
What’s a prion? Prions are proteins that are naturally produced in animals.
According to the Food and Drug Administration’s Center for Food Safety and Nutrition, abnormal prions are associated with a group of diseases called transmissible spongiform encephalopathies (TSEs), the best known of which is BSE, or mad cow disease.
Diseases caused by mutated prions include mad cow in cattle, scrapie in sheep and variant Creutzfeldt-Jakob disease in humans.
Healthy. Mice have already been produced that lack the prion protein, which led agricultural scientists to spend three years studying the effects in cattle.
Juergen Richt, a veterinary medical officer at the National Animal Disease Center in Ames, Iowa, said his team wanted to see if cattle that lacked the protein could be produced and whether they were viable.
Then the team’s $100,000 question would be whether the cattle were resistant to prion-based diseases.
At almost 2 years old, the Holstein steers appear to have no developmental abnormalities and are in good health.
Richt said the researchers have studied the steers from top to bottom, looking at weight gain, circulation and nervous systems, and even behavior and temperament. Their birth weight and weight gain are in the normal range for Holsteins.
“We could not find an obvious defect in these animals,” Richt said.
Seeing is believing. ARS, with assistance from researchers at Hematech and the University of Texas, evaluated the cattle using careful observation, post-mortem examination of two of the animals, and a technology that amplifies abnormal proteins to make them easier to detect.
Five of the seven steers on site at the animal disease center have been inoculated with a bovine prion agent, which would cause disease in animals with the prion protein. Now scientists wait to see if their modified cattle are resistant.
Richt is quick to caution that while the results look promising today, nobody knows what tomorrow may bring.
Some of the mice that lacked the prion protein had health problems as they matured, leading the scientists to approach every day with caution with their herd of Holsteins.
At least three more years of testing is planned.
Not necessary. “By knocking out the prion protein gene and producing healthy calves, our team has successfully demonstrated that normal cellular prion protein is not necessary for the normal development and survival of cattle. The cows are now nearly 2 years old and are completely healthy,” said James Robl, president of Hematech.
The company anticipates prion-free cows will be useful in studying prion diseases in both animals and humans.
According to the Hematech Web site, the company is also developing cattle that can produce human antibodies aimed at treating viral and bacterial infections and autoimmune disorders.
(Reporter Andrea Myers welcomes reader feedback by phone at 800-837-3419 or by e-mail at amyers@farmanddairy.com.)

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