Experts have found that vCJD could be passed from human to human through secondary transmission -- such as blood transfusions and contaminated surgical equipment -- 'with relative efficiency.'

Through studies on mice, they concluded that variant Creutzfeldt-Jakob Disease (vCJD) could lie in the body for many years without showing any symptoms.

Due to long incubation times for the disease, a "significant level" of underlying vCJD may already be present in the population, they said.

Human to Human Transmission

The experts also found that vCJD could be passed from human to human through secondary transmission -- such as blood transfusions and contaminated surgical equipment -- "with relative efficiency."

The study, published on-line by The Lancet Neurology, said people may not know they have the agent for vCJD and thus there is a risk "of further disease transmission" through blood transfusions or equipment.

They concluded, "A lengthy preclinical disease is predicted ... which may represent a risk for further disease transmission and thus a significant public health issue."

vCJD is the human form of BSE, also known as mad cow disease. It affects the brain and is believed to be passed from cattle to humans through eating meat infected with BSE.

Some Never Show Symptoms

Some people carry the agent but never show symptoms, while others develop the disease after many years.

It causes a change in personality, loss of body function and eventual death.

The scientists, from the National CJD Surveillance Unit and the Institute for Animal Health in Edinburgh, noted that there had been 161 reported cases of vCJD in the UK.

Last November, about 50 people who received blood transfusions were warned they may have been exposed to vCJD. In July, a similar warning was issued to about 100 blood donors whose blood was given to three people who later developed the disease.