"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

October 10, 2019

Dinobdella ferox

When it comes to parasitology, sometimes you have to get really up close with your study organism, as one researcher in Taiwan did in trying to figure out the behaviour of Dinobdella ferox - a species of leech that has a habit of getting into some uncomfortable (for its host) places.

Dinobdella belongs to a family of leeches call the Praobdellidae - unlike other leeches that simply latch onto their host's skin and start sucking, Dinobdella and most other praobdellid leeches attach themselves to and feed from the host's mucous membranes - which means they either crawl up the host's nose, or occasionally even up their urethra or anus. Because of their habit of hiding themselves in parts of the host where the sun doesn't shine, it is rather difficult to figure out just what exactly what they get up to when they are attached to the host (aside from sucking blood).

Top: a D. ferox leech poking out of Dr Lai's nose., Bottom: a D. ferox leech which has emerged after the infection period
From Fig. 1. of the paper
Dr Yi-Te Lai at National Taiwan University decided to put his body on the line in the name of science, and infected himself with some D. ferox leeches, diligently documenting his own health and the leeches' behaviour throughout entire duration. He conducted three trials, each time administering himself with a different D. ferox leech - and you can see him demonstrating his procedure for self-infection in this video.

During this period, in addition to documenting the leech's behaviour based on his first hand experience, Dr Lai also took regular trips to a local clinical laboratory to examine the leech via endoscopy, and take measurements of his red and white blood cell counts to see what effects the leech's feeding might have on his blood works.

Some the symptoms he experienced during the leeches' residency were to be expected, including nasal congestion, mild stinging sensations and some nosebleeds. But despite the leech's feeding, he found that both his red and white blood cell count held steady during the infection period, and his body was able to compensate for the blood loss. Furthermore, despite their activities in the nasal passage, they can be remarkably camera shy and were pretty good at hiding from the endoscope.

And those leeches had a ravenous appetite - during the course of their stay (which can range from 24-75 days), they grew to five to ten times their original length, and increased their body mass by up to 380 times. The juvenile leech starts out as a tiny dark mote just 3-4 millimetres long, but by the end of their stay, they were big enough to be easily noticeable when they decide to poke their head out.

Cohabiting with a bunch of nose leeches allowed Dr Lai to make round-the-clock observations and record behaviours which might not have been previously documented. After about a month into the infection period, the leeches started getting restless and were looking for a new host, and this behaviour manifested itself in some disconcerting ways.

When D. ferox starts looking for a new host, it develops an attraction to darkness and water. According to Dr Lai's account, whenever he was in a dark place such as in the middle of watching a movie at a theatre, the leeches came poking out of his nose. But this wasn't the only time when they made their presence noticeable - they also got nosy when he went about some of his daily routines like showering or washing his face. This overlapped with the ceasing of bleeding-related symptoms - which meant the leeches had finished feeding.

With their cohabitation coming to an end, Dr Lai tested out some methods for removing such leeches which have been reported in the scientific literature. His self-experimentation showed that while the leech can be coaxed out with a bowl of water, this only worked at later stages of the infection, presumably after the leech has finish feeding and was ready to move on. Once they were out, they made one final contribution to science - they were preserved in a vial of 95% ethanol and are now held at the Academia Sinica collection in Taiwan.

There is a bit of a tradition among parasitologists to infect themselves with all manners of parasites to learn more about their study organisms or test out various techniques for treatment. In this case, through self-infection, one researcher was able to shine some light on a leech which usual prefers hanging out in dark places.

Lai, Y. T. (2019). Beyond the epistaxis: Voluntary nasal leech (Dinobdella ferox) infestation revealed the leech behaviours and the host symptoms through the parasitic period. Parasitology 11: 1477-1485