Illness may help mad cow agent spread, study finds

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The agent that transmits mad cow and related diseases may spread further in the body of an animal suffering from certain illnesses, scientists said on Thursday.

Their finding raises the question of whether measures aimed at curbing the spread of mad cow disease, or bovine spongiform encephalopathy, are adequate, the researchers said.

Their tests on mice showed that prions, the protein-like fragments that transmit BSE and related diseases, can show up in organs they are not supposed to if the mouse has an inflammatory condition.

Scientists have believed that BSE-causing prions are limited to the brain, spleen, spinal cord and lymph tissue, although some tests have suggested blood and muscle tissue may also harbor the prions.

The latest study, published in the journal Science, indicates that prions may also sometimes be found in the kidney, pancreas and liver.

“We administered prions to mice with five inflammatory diseases of kidney, pancreas or liver,” wrote the researchers, led by top prion expert Dr. Adriano Aguzzi of the University Hospital of Zurich in Switzerland.

Aguzzi and colleagues in Britain and the United States inoculated specially bred mice with prions and checked to see if the prions spread in their bodies when the mice had an inflammatory condition. This is because other studies had suggested that prions might be attracted to immune system inflammatory cells.

“In all cases, chronic lymphocytic inflammation enabled prion accumulation in otherwise prion-free organs,” the researchers wrote.

BSE peaked in British cattle herds in the mid-1990s and a few cases have been reported in other countries. Canada reported its third case this month.

People who eat BSE-infected beef products can develop a related human brain disease called variant Creutzfeldt-Jakob disease or vCJD. There is no treatment or cure. It has killed 148 Britons, and five Britons are alive with the disease, according to the British Department of Health’s monthly report on the disease.

The World Health Organization says it has reports of six cases in France, one in Ireland, one in Italy, one in Canada and one in the United States.

Experts believed BSE first appeared when cattle were fed improperly rendered remains of sheep infected with scrapie, a related disease. In 1997, the United States and Canada imposed animal feed bans, and have mandated the removal of materials believed to carry infectious prions.

These include the skull, brain, nerves attached to the brain, eyes, tonsils, spinal cord and attached nerves, plus a portion of the small intestine.

The study suggests that even symptom-free animals may also have prions in their livers, kidneys and pancreases. 

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