Tainted crack and cocaine laced with a chemical that can kill is surfacing in London after years of wreaking havoc in big-city Canada and the U.S.

A nurse with London’s InterCommunity Health Centre discovered an infection caused by the chemical in a cocaine user in January, Henry Eastabrook, a centre outreach worker, confirmed Friday.

The centre is warning outreach and addiction workers in London about the chemical, a livestock deworming agent called levamisole.

“It can kill you if you continue using it. It attacks your immune system,” Eastabrook said.

Levamisole can cause agranuloctyosis, a dangerous reduction of white blood cells, which impairs the body’s ability to fight off even minor infections.

Cocaine and crack users with dark bruises that turn into scabs, often around the ears, or a rapid onset of fevers and chills should head to hospital emergency rooms immediately, the health centre warns.

It’s not clear how widespread the tainted cocaine is in London. Police couldn’t be reached for comment Friday.

Eastabrook suspects London has been spared so far, because most of the cocaine here is distributed from Montreal, where perhaps an older, untainted stash has been the main source.

“We haven’t had a major outbreak yet. When the supply dries up, I suspect we will see more of it.”

He also warned that cocaine is “still the drug of leisure” for many socio-economic classes in London, meaning that people from all walks of life will be affected by the tainted product.

Two years ago, crack ranked as the fourth-most common substance abuse problem at Addiction Services of Thames Valley in London, with cocaine fifth.

Infections caused by levamisole are treatable.

But in the U.S. some deaths have been attributed to levamisole-laced cocaine and in the fall of 2009 the U.S. federal health department issued a nationwide public health alert about the chemical.

Since late 2007, cocaine suppliers in Colombia — a major world source of the narcotic — have been cutting more and more of the illicit drug with levamisole, said the U.S. Drug Enforcement Administration (DEA).

By 2009, about 71% of the tested cocaine contained levamisole, the DEA said in its 2010 National Drug Threat Assessment.

It’s still not clear to police, addiction counsellors or users why the coke is being increasingly cut with levamisole.

It may be added to make the amount of cocaine appear larger, and still look pure, as when the drug is bulked up with other cheap ingredients to make the quantities appear larger. The chemical also has a similar stimulating effect as cocaine.

“You can’t smell or taste it,” Eastabrook said.

A doctor in Seattle has developed a kit that helps users test cocaine to see if levamisole is present, he added.