Four people have been infected with what doctors believe is botulism while injecting drugs, according to the Department of Health.

The Public Health Laboratory Service is investigating three suspected cases in England and one in Scotland.

It is thought the four contracted the disease through contaminated heroin.

A warning has now been issued to drug users and health care professionals across the UK.

Prove fatal

The rare condition is caused by bacteria that poison the body if injected.

More than 90% of cases are treated successfully - but some prove fatal.

Early symptoms - blurred vision and difficulty swallowing and speaking - can quickly progress to include paralysis and breathing problems.

A spokesman for the Public Health Laboratory Service said any drug users with these symptoms should immediately seek medical help.

'Unprecedented outbreak'

He added that, as precautionary measures, heroin users should try to use as little citric acid as possible while injecting and refrain from sharing needles.

Last year, 40 addicts across the UK and Ireland, including 18 from Glasgow, died after contracting an illness which caused severe inflammation of vital organs from infected heroin.

A health board report described an "unprecedented outbreak of severe illness" among 60 users in Scotland, mostly in Glasgow, between April and August 2000.

And it identified the bacterium clostridium novyi - from the same family of organisms as wound botulism - as the cause of the illness.