Worries over test for mad cow disease

Oct 21 2008

A new test to screen blood for the incurable human form of mad cow disease could be available within 18 months, but it has raised concerns.

The breakthrough blood test which will be able to diagnose variant Creutzfeldt-Jakob diseases (vCJD), is currently undergoing clinical trials but experts are worried it will reduce the number of people prepared to donate blood - research suggests 1 in every 4,000 people might harbour vCJD in their blood, though 95% of them may never actually develop the full blown disease.

Variant CJD is a rare and fatal human neurodegenerative condition and is a Transmissible Spongiform Encephalopathy (TSE) or prion disease - because of the characteristic spongy degeneration of the brain - it is strongly linked to exposure, probably through food, to a TSE of cattle called Bovine Spongiform Encephalopathy (BSE).

In the early stages patients usually experience psychiatric symptoms such as depression or, less often, a schizophrenia-like psychosis.

Unusual sensory symptoms, such as "stickiness" of the skin, have been experienced by half of the cases early in the illness and neurological signs, including unsteadiness, difficulty walking and involuntary movements, which develop as the illness progresses; by the time of death, patients become completely immobile and mute.

There are at present no available, completely reliable diagnostic tests for use before the onset of clinical symptoms, but magnetic resonance scans, tonsillar biopsy and cerebrospinal fluid tests are useful for detection.

The highest incidence of vCJD is in the UK, the country with the largest potential exposure to BSE. A statutory ban on the feeding of protein derived from ruminants (e.g. cattle, sheep and goats) to any ruminant exists.

The use in the food chain of bovine offals thought to pose a potential risk to humans was also banned in the UK in 1989.

According to advisers to the British government, though the test is undoubtedly a significant step towards eliminating the incurable disease and preventing it from becoming endemic in society, it could result in a reduction in the number of blood donors and there are also fears it could increase insurance premiums.

Experts suspect that donors will be reluctant to give blood if they risk being told that they have the possibility of developing the disease which causes a horrible and agonising death.

Dr. John Forsythe, chair of the Advisory Committee on the Safety of Blood Tissues and Organs (SABTO) and a transplant surgeon at the Royal Infirmary of Edinburgh says the test does have significant downsides, despite concerns that the disease could become widespread in the UK.

However only 4 of the 167 people who have died from vCJD contacted it through infected blood - but the knowledge of having the disease would be terrifying prospect.

The problem is compounded because around 1% of the positive tests could be wrong and with two million people donating blood every year in Britain that could amount to 250 people being told they had the infection, and up to four of them being falsely diagnosed.

Experts say from both a legal and ethical standpoint, those incubating the disease would have to be told even though only a few could develop it fully.

In 2004 vCJD had an impact on blood supplies when the number of blood donors dropped by 52,000 when those who had received blood transfusions in the previous two decades was banned from donating blood.

Currently donated blood is screened for HIV, syphilis and hepatitis B and C, but because vCJD is neither curable or treatable, many donors may prefer to not know they could develop the progressive and fatal degenerative brain disease.

Presently vCJD is tested for by performing post mortem biopsies on the brain.