Second Human Mad Cow Blood Case Raises Concerns

August 5, 2004
By Patricia Reaney

LONDON (Reuters) - Britain's second suspected case of transmission of the human form of mad cow disease through a blood transfusion could mean more people will become infected with the deadly illness, a medical expert said Friday.

Professor James Ironside, of the National CJD Surveillance Unit in Edinburgh, which monitors and studies the illness, said the case shows blood transfusion is an effective means of transmission and that people with different genetic makeup from previous patients are also susceptible.

"The patients we have seen so far may just be the first of a series of groups of patients. The idea that vCJD somehow is a disappearing disease -- I think we can't entertain that anymore," he said in an interview.

The government announced what was thought to be the world's first case of transmission of variant Creutzfeldt-Jakob disease (vCJD) via transfusion last December after a patient died several years after receiving blood from a donor later found to have had the illness.

The second suspected case was reported last month.

But unlike all the other cases of vCJD, the elderly patient, whose case is reported in The Lancet medical journal, belonged to the largest genetic subgroup which includes over 50 percent of the population. All the other patients belonged to a smaller genetic subgroup.

"This really reinforces the fact that vCJD is a problem that still has potentially quite a long future ahead of it," Ironside explained.

LONG INCUBATION PERIOD

Variant CJD is the human equivalent of Bovine Spongiform Encephalopathy (BSE) or mad cow disease, which is linked to eating meat infected with BSE. The illnesses are caused by brain proteins that transform themselves into infectious agents.

According to the Department of Health 142 people have died from probable or definite vCJD. The incidence of the illness has been declining recently, sparking hopes it could be the beginning of the end of the problem.

But Ironside said the identification of the infectious agent in the most common genetic subgroup means it probably isn't.

"It indicates quite clearly that people can be infected by this agent. They can be asymptomatic but can still carry the agent and at some point in the future may develop the disease.

"In the meantime they represent a risk to others of transmitting the disease through blood transfusion ... or perhaps through contamination of surgical instruments," Ironside explained.

The second patient did not die of vCJD but an autopsy showed the infectious agent in the spleen. The patient had a blood transfusion five years earlier from a person who later developed vCJD.

Studies of other types of prior disease have shown that patients in the largest genetic subgroup have the longest incubation period, which is consistent with what scientists have found in the patient.

Until now all people with vCJD have been in the less common genetic subgroup and may have been the most susceptible and with the shortest incubation period.

"There may be an unknown number of other people in the UK who have been exposed to BSE but because of their genetic background they will have a long incubation period and therefore we can anticipate more cases in the future," Ironside said.

"We've shown that individuals in the commonest genetic subgroup are susceptible to variant CJD infection. There is no doubt about it."
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