Study Points to 'Mad Cow' Blood Risk for Humans

April 7, 2001 Reuters by Greg Frost

PARIS (Reuters) - Monkeys can contract mad cow disease if it is injected into their bloodstream, underscoring that infected tissue risks transmitting the brain-wasting illness to humans, researchers said on Friday.

French scientist Corinne Ida Lasmezas said that she and a team of French and British scientists proved that the agent that causes mad cow disease, or bovine spongiform encephalopathy (BSE), can be passed from one primate to another intravenously.

She warned, however, that the study had not proven that vCJD can be passed to humans through the blood supply.

``Everything depends on the amount of the infectious agent in blood -- we don't know if there is enough in human blood to infect another human,'' she said.

The team's research, published last week in the U.S. journal Proceedings of the National Academy of Sciences, dealt with the behavior of prions -- the distorted proteins blamed for causing BSE and its human equivalent, new variant Creutzfeldt-Jakob Disease (vCJD) -- in primates.

``We wanted to better understand the behavior of the BSE agent in primates to have an idea of the risk that vCJD poses in humans,'' Lasmezas told Reuters in a telephone interview.

``Effectively, this is the first time BSE has been passed between primates via blood,'' she said.

She said the study had also shown that the BSE prions become more virulent to primates after they have replicated in primates. They would lie dormant for less time when passed from one primate to another than when they cross from cattle to primates.

Sick Monkeys

In the study, Lasmezas and her team first infected macaque monkeys by taking concentrated samples of the mad cow agent from brains of infected humans and cattle and injecting them directly into the monkeys' brains.

They then took samples from the infected monkeys' brains and injected them into the brains of healthy monkeys. They also took samples from the brains of sick monkeys and injected them into the veins of other, healthy monkeys.

The researchers found that all monkeys that were injected with the agent -- either into the bloodstream or into the brain directly -- became sick with the fatal disease.

More importantly, however, the scientists found that the BSE agent lies dormant for a shorter period of time once it adapts to primates. ``This means that once the agent has adapted to primates, it's more virulent for another primate,'' she said.

Prions have puzzled scientists since they were discovered. Normally present in the brain and other tissue of mammals, they can take on an abnormally folded form that causes the brain to become spongy and eventually wither.

It is generally thought that prions can propagate, clump up and cause disease without the use of any kind of genetic material at all, unlike viruses, bacteria and parasites.

They are blamed for a range of diseases known as transmissible spongiform encephalopathies that include BSE in cattle and vCJD in humans.

At least 85 people in Britain and two in France have died from vCJD.

Because neither the incubation period for vCJD in humans nor the dose required to infect humans is known, scientists do not know how many more people may be infected by the agent.

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