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Meet Macrobdella mimicus: Researchers identify new species of medicinal leech

You might think of leeches as something to avoid.

But the bloodsucking parasitic worms still play a part in modern medicine — and researchers like Sebastian Kvist of the Royal Ontario Museum in Toronto have been seeking them out.

Kvist, the ROM's curator of invertebrates, is one of four co-authors of a report by an international team of scientists that made the first discovery of a new North American medicinal leech species in more than 40 years. Their study was published Thursday in the Journal of Parasitology.

The ROM is home to a leech now considered a member of the new species. It's no longer alive, but is housed in a jar. Kvist said when he first received the leech a few years ago he knew something was different.

"I was very, very happy that we had them here," Kvist told CBC Toronto during an interview in his lab. 

"It's a good thing to distribute individuals of this species throughout the world in different museums or natural history collections so that we do have a repository of the species around the world should something happen," he said.

A team led by Anna Phillips of the Smithsonian National Museum of Natural History found the species in Maryland in 2015 while investigating genetic variations of leeches. They initially thought the leech they found was of a species that had already been identified, but DNA sequencing revealed otherwise.

The 2015 discovery prompted the team to look for more.  

Phillips's team searched through marshes and ponds looking for live leeches, but they also asked museums to take another look at existing specimens. After analysis, researchers learned that dozens of the new species, named Macrobdella mimicus, had been preserved in museums for years without scientists knowing they were a different species.

They eventually discovered the new species has long called the region between the Appalachian Mountains and the eastern coast of the U.S. home. 

Anna Phillips, curator of parasitic worms at the Smithsonian's National Museum of Natural History, led the international team of scientists that discovered the new leech species. (Paul Fetters for Smithsonian )

"We were really excited," Phillips said. "There's four species known and everyone thought these were pretty well characterized. We thought we knew them pretty well."

She said the leeches were never far away — the new species were found less than 80 kilometres from the Smithsonian, where she is the parasitic worms curator.

"It just goes to show that there's a lot [of] unrecognized diversity," Phillips said.

Over a two-year period, the team examined 147 of the new leeches, 60 of which came from museums.

As part of the study, Kvist helped sequence the leech's DNA and compared it with the quintessential North American medicinal leech species called Macrobdella decora. He was able to confirm the new species.

He said there's a five to 10 per cent difference in DNA between the two species, but the physical differences are best seen under a microscope.

Sebastian Kvist, the Royal Ontario Museum's curator of invertebrates, helped sequence DNA to confirm a new species of North American medicinal leech. (Chris Langenzarde/CBC)

"Those differences are quite minute for non-leech experts, but for us, they're actually quite significant," Kvist said.

He said the discovery allows people to better understand the ecological diversity that surrounds us and the fundamentals of biology – knowing which species lives where and how they interact with each other.

"You can't conserve or protect something that you don't know what it is," he said.

Notorious bloodsuckers 

Medicinal leeches have been used medically for centuries in various countries, according to Jacalyn Duffin, professor emeritus of medicine at Queen's University.

"They were probably used before writing began," she said.

It was believed ridding the body of bad blood could help cure ailments including headaches, fevers and disease.

They are still used at Toronto Western Hospital's combined surgical unit for post-operative patients.

"It's pretty amazing what leeches are able to do," said April Huang, a nurse educator at the hospital.

Leeches are used on about one-third of patients who have had a finger amputated and reattached by surgeons, according to Huang.

The leeches help manage some post-surgery symptoms, and can prevent complications. They are also used to facilitate blood flow.

The Royal Ontario Museum is home to one specimen of the newly identified leech species. (Angelina King/CBC)

Huang said not only do they suck out congested blood, they can dilate blood vessels to increase blood flow and prevent clotting. Their saliva includes an anesthetic property that produces a numbing effect and has proteins that help with anticoagulation.

Kvist said the discovery of the new species doesn't equate to any concrete changes in the medical field, but it could eventually help patients.

"We're hoping that down the line the knowledge of this new species will help us to find new anticoagulants or new blood thinners that these leeches have in their saliva and that might be of benefit."

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