Cow to Cow mad Human disease possible?

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Human-to-Human 'Mad Cow'-Like Infection Possible

By Amanda Gardner

HealthDay Reporter

 

 

People may be at risk for contracting the human version of mad cow

disease, even if they haven't eaten parts from an infected animal, a

new study contends.

 

Instead, new experiments with mice suggest that human-to-human

transmission via blood transfusions, unsterilized surgical

instruments or other means could be a relatively easy mode of

infection with the deadly disease.

 

British researchers say variant Creutzfeldt-Jakob disease (vCJD), the

human version of the disease, was more easily transmitted in mice

producing a human gene than bovine spongiform encephalitis (BSE)

or " mad cow " disease, the animal version.

 

vCJD, which is caused by a distorted protein called a prion, also

infected mice with gene variants that had previously been thought to

be immune to the illness.

 

" It means that we should be aware and keep an open eye and set up the

best possible measures to avoid human-to-human transmission because

we have to count on the fact that there might be more asymptomatic

carriers that we know of, " said Dr. Corinne Lasmezas, professor of

infectology at Scripps Florida in Jupiter. " But it doesn't mean that

it will be a huge epidemic. "

 

Lasmezas wrote a " reflection and reaction " paper that accompanied the

study. Both appeared Monday in the journal The Lancet Neurology.

 

The total number of human vCJD cases worldwide now stands at 190. The

incubation period is so long, however, that the toll may rise

anywhere from the low hundreds to the hundreds of thousands, the

study authors stated.

 

In August 2004, British authorities reported evidence that vCJD might

be spread by blood transfusion. The misfolded prions characteristic

of vCJD were detected in an elderly person who received a blood

transfusion in 1999 from a donor who developed the disease after the

donation and died in 2001.

 

The transfusion recipient, whose age and sex were not disclosed, did

not have symptoms of the disease and died of other causes.

 

Another case of transmission linked to a transfusion involved a

victim who developed symptoms of the disease six-and-a-half years

after receiving a transfusion. In that case, the donor developed

symptoms three years after the donation and died of vCJD.

 

Because of the potential risk, the United States does not accept

blood donations from people who spent at least five months in Europe

since 1980 or who spent three months in the United Kingdom between

1980 and 1996.

 

No human equivalent of mad cow disease has yet been found to have

originated in the United States, but three BSE-infected cows have

been identified.

 

For the new study, Edinburgh-based researchers engineered mice to

carry one of three different human gene variants, known as MM, MV or

VV. Among Caucasian humans, 50 percent of individuals are MV, 40

percent are MM and 10 percent are VV.

 

All of the human cases of vCJD thus far have been in people who are

MM. One person who tested positive for prions but died of other

causes was MV.

 

" As far as clinical cases, being MM seems to be a particular factor

of susceptibility, " Lasmezas said. It had been thought -- or hoped --

that other gene variations were less susceptible. The MV person, she

added, " was the first hint that MV people might be susceptible. "

 

The researchers then inoculated the engineered mice, along with mice

which had bovine genes, with either vCJD or BSE.

 

BSE was transmitted to the bovine line but not to the human lines;

vCJD, on the other hand, infected all three human lines.

 

" This means that as far as we can extrapolate to humans, which is

something we always have to be careful with, all genotypes allow

infection so all humans could be potentially infected if they have

been exposed to a sufficient amount of the infectious agent, "

Lasmezas said.

 

There was, however, a gradation of susceptibility. Most mice that

were infected were MM, followed by MV, who were infected at about the

same rate but developed the infection later. Transmissions were much

lower among VV mice, indicating that this variant might be

protective.

 

" If this is true in humans, there may be as many MV people incubating

but they might develop the disease later or might never develop the

disease, but we have to count on the fact that there might be MV

people who are infected and are subclinical [no symptoms] carriers, "

Lasmezas said.

 

One positive note: The study mice were infected directly with brain

material, meaning the findings may be less relevant and less alarming

to humans.

 

" This was brain-into-brain and that doesn't occur very often, " said

Dr. Carol K. Petito, professor of pathology at the University of

Miami Miller School of Medicine. " It's a mistake to say this never

will happen... [but] human-to-human transmission will be less

efficient. "

 

More information

 

Visit the U.S. National Library of Medicine to learn more about

Creutzfeldt-Jakob disease.

 

 

brain to brains.......bob