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While an influx of blood-sucking leeches, caused by Australia’s recent spell of wet weather has been lamented by some, surgeons and nurses across NSW are rejoicing.

The Black Summer bushfires of 2019 and 2000 caused a shortage of the parasitic worms, which have been branded “godsends” in the medical field.

Dr Sarah Tolerton, a plastic and reconstructive surgeon at Sydney/Sydney Eye Hospital who specialises in adult and paediatric hand surgery, said leeches are invaluable medical tools used to save fingers – and lives – across NSW.

A leech sighted in Sydney's Lavender Bay at the end of April.
A leech sighted in Sydney’s Lavender Bay at the end of April. The species used in medicine is not your garden-variety leech it’s a specially bred species from Victoria. (Supplied)

“The biggest problem we have after surgery if we’ve successfully replanted the finger is venous congestion,” Tolerton told 9news.com.au, adding most injuries she sees are sustained in the workplace involving power tools.

“What the leeches allow us to do is to kind of take on the role of the veins, or relieve that congestion.

“That way the tissue that’s been replanted doesn’t get too engorged and can survive.”

Tolerton works across a number of hospitals in Sydney, including Sydney/Sydney Eye Hospital and said a number of sites now have established “tanks” for the leeches.

A tank of medicinal leeches are seen at Sydney Hospital and Sydney Eye Hospital.
A tank of medicinal leeches are seen at Sydney Hospital and Sydney Eye Hospital. (Kay Maddison)

The species used is a specially-bred variation called Hirudo medicinalis. It’s bred in a water channel off the Murray Darling by a couple in northern Victoria.

Tolerton said no other human-invented technique works quite as well as these creatures, which evolved about 150 million years ago.

This is partly due to the anticoagulant peptide, Hirudin, in their saliva, which prevents blood from clotting when they latch on.

“There’s lots of things actually,” she said, adding patients are normally given an antibiotics to mitigate the small risk bacteria could be spread by the animals.

“Leeches secrete other substances like histamine and hyaluronidase; which dilate and allow access to the vessels.

“And the final thing is they suck, they’re multipurpose. The combination of these things means they are more powerful than many other techniques in the salvage of tissue.

“They really are godsends”

Leech saliva contains an  anticoagulant peptide called Hirudin, which prevents blood from clotting. When it comes to establishing blood flow this is crucial.
Leech saliva contains an anticoagulant peptide called Hirudin, which prevents blood from clotting. When it comes to establishing blood flow this is crucial. (Kay Maddison )

Tolerton said should a leech shortage occur, like when the bushfires happened, the alternative is to remove the nail to expose the nail bed or open up the tissues, and apply a synthetic anticoagulant called heparin.

“It’s far less effective,” she said.

“The leech can suck the blood but also injects all the bioactive goodies – they’re just incredible.”

Clinical Nurse Consultant at Sydney/Sydney Eye Hospital Kay Maddison works closely with the leeches.

Any patient receiving leech therapy is given a preventative course of antibiotics to mitigate the small risk bacteria are also spread by the parasites.
Any patient receiving leech therapy is given a preventative course of antibiotics to mitigate the small risk bacteria are also spread by the parasites. (Kay Maddison)

She said 22 patients were treated with the parasites from 2017 to 2022.

Six of these cases – the highest case load over this five year period – were last year.

“New nurses can get a little bit concerned but they soon get over it,” Maddison said.

“They know they do a good job.

“Patients can be squeamish about it as well, but they get over it too. They actually tend to name them.”

When it comes to the length of time the animal is left on, Maddison said “every leech varies”.

“We allow them to fully feed and detach themselves,” she said.

“They can last for half an hour, they could last for four hours.”

The history of leech therapy

The practice of bloodletting, removing some of a patient’s blood for therapeutic purpose, has a long history that spans at least 3000 years.

The first recorded instance of leeches being used for bloodletting “appears in a painting in an Egyptian Tomb of around 1500 BC”, according to a paper published in the National Library of Medicine.
Thomas Major's engraving 'Le Chirurgien de Campagne' (1747) depicts a man having leeches applied to his foot.
Thomas Major’s engraving ‘Le Chirurgien de Campagne’ (1747) depicts a man having leeches applied to his foot. (Supplied)

The practice reached the height of its popularity in the 17th and 18th century AD in Europe.

In fact, it was so popular during this period there was shortage of leeches in certain European countries due to over-use. It’s estimated five to six million leeches were used in Paris alone each year, and about 35 million in the country as a whole.

But enthusiasm for leeches started to wane by the end of the late 18th century.

And by the 1870s and 1880s modern germ theory, the theory certain diseases are caused by invasion of microorganisms, emerged.

The Colombian Dwarf Gecko is incredibly small and only reaches two centimetres long. But it boasts an impressive history; it has been around since the age of the dinosaurs.

The world’s rarest animals

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