LONDON - Scientists have pinpointed a highly toxic bacteria as the cause of a mysterious illness that has killed at least 35 heroin addicts, public health officials said Thursday.
The source of the illness, which emerged first in Glasgow and also has been found in other areas of Scotland, England and in Dublin, Ireland, had baffled health chiefs for more than a month. Sixty-four infectious cases have been confirmed.
Scientists at the Public Health Laboratory Service in Cardiff, Wales, and experts at the U.S. Centers for Disease Control and Prevention in Atlanta identified the culprit as the clostridium bacterium.
Experts believe a batch of heroin was probably accidentally contaminated with the bacteria when the drug was being mixed with other substances before sale.
Dr. Jai Lingappa of the U.S. centers said scientists still need to clarify exactly how the bacteria contributed to the illness.
''We also want to learn more about why these people became sick and others didn't,'' he said.
The bacteria, Clostridium novyi Type A, is commonly found in soil and dust and can occur in animal droppings. It grows only when there is no oxygen, which makes it difficult to identify in a laboratory. It is closely related to others in the clostridium family that cause mild food poisoning, tetanus and botulism.
Dr. Laurence Gruer of the Greater Glasgow Health Board said it was unclear where in the delivery line the bacteria had contaminated the heroin.
''That is something we can only speculate on. There is a long route bringing the heroin into the British Isles,'' he said, adding that it could have happened at any point between western Asia, the suspected source of most of Britain's heroin, and Britain.
Gruer said he ''hoped and believed'' the outbreak was an isolated one.
Health officials said Type A clostridium bacteria were responsible for outbreaks of gas gangrene during both world wars, but that the bug this time is thriving in citric acid, which is sometimes mixed with heroin.
The problem occurs when the drug is injected into muscle, rather than a vein because the acid burns and kills muscle tissue. The bacteria infects the dead tissue and multiplies there, releasing a toxin that enters the blood and can damage distant organs, prompting the body to go into a deadly toxic shock.
The affected addicts suffer initially from swelling around the point where the needle entered the skin. The patient then usually suffers toxic shock.
''Clostridium novyi Type A is well known as a cause of severe infection in domestic animals, but rarely does so in humans,'' said Dr. Brian Duerden, medical director of the Public Health Laboratory Service in Cardiff. ''As far as we know this is the first time this bacterium has ever caused an outbreak of infection in drug injectors.''
If found early enough, the bacteria can be killed by antibiotics, and surgeons can remove infected tissue, health officials said. But the resulting toxin is resistant to antibiotics and very poisonous.
Gruer said the most accurate figures available to date showed that 20 people in Scotland, eight in Dublin and seven in England and Wales had died of the illness.
Other health authorities also are investigating deaths that may bring the total to 39, and three deaths in middle England that police said were linked to the illness have not been included in the figures, Gruer said.
The Glasgow health board has advised heroin addicts to smoke the drug rather than inject it.
