Tongue May Harbor
'Mad Cow' Prions
By Alison McCook

NEW YORK (Reuters Health) - New research suggests that the errant proteins that cause "mad cow" disease in cattle and a similar brain disorder in humans can travel from the tongue to the brain and vice versa.
The experiments were performed in hamsters, and did not use the same type of abnormal proteins that cause mad cow disease.
However, if similar findings are discovered in animals that can sicken humans, it would suggest that eating beef tongue and products that contain beef tongue may put people at risk of the deadly human ailment known as new variant Creutzfeldt-Jakob disease (vCJD).
What's more, the researchers found that placing the prions on a small wound in the tongue was a highly efficient way to spread the disease, more so than actually eating the proteins.
Mad cow disease, or bovine spongiform encephalopathy (BSE) as it is officially called, is an incurable brain-wasting disease in cows, which Britain first detected in herds in1986. Since then, more than 100 people in Europe, almost all of them in Britain, have developed vCJD from eating BSE-infected meat.
BSE, vCJD and other related illnesses, such as the animal disease scrapie, are marked by the build-up in the brain of abnormal versions of proteins called prions.
Although people fall ill after eating infected meat, in the January issue of the Journal of Virology, Dr. Richard Bessen and his colleagues report that not all hamsters that consume foods that can lead to prion disease become sick as a result.
However, when the researchers injected the prions into the tongues of hamsters, they found that all animals became infected with prions, and did so more quickly than if they had eaten disease-causing food.
"Inoculation into the tongue was more efficient than ingestion," Bessen told Reuters Health.
Bessen and his colleagues also discovered that all hamsters with a small lesion on their tongues became infected with the disease after eating infected food. These hamsters became infected more slowly than when the prions were injected into the tongue, but faster than if they had eaten the food without a tongue lesion.
These findings suggest that cuts in the mouth put eaters of foods that can cause prion disease more at risk of disease than otherwise, Bessen noted.
The researchers also found that after injecting prions into the brains of hamsters, prion infection spread to the animals' tongues, indicating that the tongue can serve as a reservoir for prion disease.
In an interview, Bessen explained that prions travel along nerves, and the tongue is attached to a vast network of nerves. He noted that prions likely move between the tongue and the brain using that nerve highway, by traveling along the nerve that enables the brain to control the movement of the tongue, and the nerves that reach the tastebuds.
Bessen said that the next step is to determine whether the same process occurs in sheep and cows, the animals whose prion diseases may put humans at risk. In the new study, the researchers used a type of prion known to cause disease in mink.
"Whether (these experiments) have relevance in natural infections, we really don't know," Bessen said.
SOURCE: Journal of Virology 2003;77:583-591.
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