Bleeding-edge research into some of the nation's rarest invertebrates

Posted 9 Aug 2024 in Highland Wildlife Park

Medicinal leech

IMAGE: RZSS

At Highland Wildlife Park we have conservation breeding-for-release programmes for five invertebrate species: pine hoverflies, dark bordered beauty moths, medicinal leeches, blood red long horn beetles and pond mud snails. As an RZSS vet I am involved in keeping all the animals that we have at the park healthy, but recently I have been undertaking some exciting work with our invertebrate species conservation projects.

My involvement is mostly as a sort of ‘disease risk assessor’ for the releases of all those invertebrate species back into the wild. We make sure that the populations we breed are healthy, but also that we're managing and breeding them in a manner that is bio-secure so that when those animals are released into the wild, they're not going to be taking any diseases with them.

On the opposite end of the spectrum, we need to check when we're bringing individuals in from the wild, such as the medicinal leeches, that we're not also bringing anything into the breeding for release centre. This requires veterinary testing for invertebrate diseases, post-mortem examinations, helping the team to write their quarantine protocols and treating any animals that fall ill while living in the conservation breeding programme.  

There's not a lot of research done on medicinal leech health - as you can imagine. Most of what is published in relation to leeches refers to their relevance to human medicine (some other species of leeches are still used in human medicine today). In attempting certain treatments to help sick leeches we have been undertaking investigations into the species that have never been done before.

And we have had some great successes. We used an antibiotic treatment in a very sick individual and they got better! Choosing the correct antibiotic was a challenge. We swabbed the leech and sent that away to a laboratory to get a culture and sensitivity report back that tells us which bacteria are present and which antibiotic ingredients could kill them.  

Once we have that we then need to look at what different formulations the appropriate antibiotics come in. Obviously, a leech can't swallow a tablet, so that's no good. We steered away from injections, partly because where would we give an injection? There isn't really any data on how to do that safely. We also don't want to disrupt the microbiome of the leeches’ gut with antibiotics added to water.

We also have to be very careful of their skin because they're aquatic creatures, so we have to be mindful of anything that they come into contact with. There are lots of products that are used for fish, and with leeches being aquatic that seems like a sensible way to go, but leeches don't have skin like a fish. They have a mucosal membrane, which is very, very sensitive. It's like the surface of your eye or the inside of your mouth. A lot of the products that were suitable for fish could be painful for the leeches.  

I ended up treating the leech as if it were a frog with no bones, and used an antimicrobial preparation that was designed to be gentle on the skin. We went for ear drops; it was a product that's used for infected ears in dogs that contained the correct antibiotic ingredients and was in a topical preparation that we hoped wouldn't irritate their skin and it worked, with the leech making a full recovery.

There is still a long way to go before we can understand leech health as well as we do some of the other species we care for but the longer we work with the species, the more we can discover.

Dr Rebecca Amos

Royal Zoological Society of Scotland (RZSS) Veterinary Surgeon

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