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Holy spit, Batman!! A new study has found that a substance that vampire bats inject into their victims could be far more effective in preventing damage from strokes than the drug now being used.

Strokes, the fourth leading cause of death in Canada, usually happen when blood clots block the flow of oxygen and nutrients to the brain. Vampire bats secrete a potent clot buster in their saliva that one day could help millions of people.

"When the vampire bat bites its victim, it secretes this powerful clot-dissolving substance so that the victim's blood will keep flowing, allowing the bat to feed," said Robert Medcalf, an Australian researcher and author of a study in yesterday's edition of Stroke, published by the American Heart Association.

The bat compound, known as DSPA, was replicated in the lab in the early 1990s, so patients now taking part in clinical trials are being given an artificial version, not something actually extracted from vampire-bat spit. There are no results from human studies yet, but new research in mice shows that the bat compound may be better than the existing treatment because it can be used much longer after a stroke occurs.

The drug now being used, known as TPA, revolutionized the treatment of strokes. It was approved by Health Canada in 1999 and gave doctors a much greater chance of helping patients survive a stroke with little or no disability.

But it can only be administered within two to three hours of a stroke. After three hours, there may be an increased risk of bleeding in the brain. As a result, TPA is now available to only a fraction of the 50,000 Canadians who suffer a stroke every year. The rest aren't taken to hospital in time.

The researchers are looking at ways to improve the treatment of people with ischemic strokes, the most common kind of stroke, which occurs when a blood clot or constricted blood vessels prevent blood from getting to the brain.

Dr. Medcalf compared both drugs, and found that the bat compound worked better than TPA in mice and can be administered up to nine hours after a stroke. It is now being tested in that context for stroke patients in Europe, Asia and Australia. A U.S. study could begin this year.

The nine-hour window would allow patients to undergo imaging tests to make sure they have had a serious stroke before getting the medication.

There was also less risk of brain damage with the new compound, Dr. Medcalf says.

It targets and destroys fibrin, the string-like substance that forms when a clot is formed and that holds it together. It is only activated in the presence of fibrin, which means it is less likely to cause collateral damage in the body.

"There is an advantage to having a substance that only works when a blood clot is present," Dr. Medcalf said.

Other researchers were cautious about the development, saying that clinical trials in humans are needed to show whether the bat compound will live up to its potential. There may not be an advantage to having an extra six hours to administer the drug because many researchers believe the brain damage from a stroke is irreversible after three hours.

Dr. Medcalf was also involved in the development of TPA, which is similar to the bat-saliva compound, but less potent.

He says scientists have known since the 1960s that vampire bats, which feed on the blood of large birds, cattle, horses and pigs, produced something in their saliva that broke up blood clots.