"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

February 13, 2017

Trichodectes pinguis

Today we're featuring a guest post by Aidan McCarthy - a student from 4th year class of the Applied Freshwater and Marine Biology' degree programme at the Galway-Mayo Institute of Technology in Ireland. This class is being taught by lecturer Dr. Katie O’Dwyer and this post was written as an assignment about writing a blog post about a parasite, and has been selected to appear as a guest post for the blog. Some of you might remember Dr. O'Dwyer from previous guest post on ladybird STI and salp-riding crustaceansI'll let Aidan take it from here

The words parasite and lice regularly go hand in hand, and usually brings us dreaded flashbacks to those primary school days when our parents would rigorously comb and shampoo our hair trying to rid of us those nasty headlice! Well unfortunately for Scandinavian brown bears, lice may impose a bigger problem than just an itchy head as a team of Swedish scientists found out in their recent study.

Trichodectes pinguis specimen from Fig. 4 of the paper
Trichodectes spp. hit the limelight when these “pests” were discovered in our beloved pets, often resulting in scratching, sleeplessness and nervousness in man’s best friend. This lead to the cull of Trichodectes canis from dogs in the western world through veterinary practices.

However, Trichodectes don’t just occur on dogs, with previous studies discovering 16 species within this genus (no doubt there are hundreds more waiting to be discovered!) parasitising ungulates and carnivores worldwide. Trichodectes pinguis are chewing lice or biting lice of brown bears, although this name suggests they bite and chew their host, they actually feed on their dead skin and other skin products.The side effects caused by this feeding can be major irritants to brown bears as you’ll see later. These are permanent ectoparasites that stay their entire lifecycle on their host, and are highly specific to brown bears. They get transmitted between bears through direct physical contact during mating, fights, and mother-offspring contact.

Patches of hair loss in the neck and upper chest region of the infected bear
From Fig. 1 of the paper
In the April of 2014, a 5-year-old female brown bear was captured by scientists in south-central Sweden under the Scandinavian Brown Bear Research Project and after extensive examination, patches of baldness were discovered on its neck and upper part of its chest. This was caused by, you guessed it, those foraging little critters. Similar but more extreme cases were observed in two male bears the following year who had extensive patches of “bearness” throughout their bodies. Moderate to high numbers of these tiny lice were found in the hair surrounding the affected areas.

The affected areas showed signs or hyperpigmentation, lichenification, and in some cases chronic dermatitis indicating inflammation, pruritus and severe scratching, so pretty nasty hey! We all know the feeling of having an itch that just won’t go away, now imagine that on most of your body. Interestingly, hair samples collected from nearby brown bear day beds (hidden resting places) were found to contain lice too.
Left: Capture male brown bear parasitised by lice with patches of hair loss, Right: the same bear capture on camera feeding
From Fig. 2 of the paper
Mammals often carry considerable numbers of ectoparasites without any major effects to their health, yet more intense infestations as observed on those brown bears can have detrimental effects to the host. These severe louse infestations can make bears more susceptible to secondary infections and negatively alter their behaviour with restlessness, scratching, reduced feeding times and high levels of stress being just some examples.

Finally, if those weren’t bad enough, excessive hair loss may affect thermoregulation of the animal especially during times of high energy expenditure such as reproduction and hibernation. It would be pretty chilly going to sleep on a cold winters night without your warm woolly duvet alright! So I think it’s safe to say we didn’t have it too bad with those pesky headlice when you think about what the poor Scandinavian brown bears have to deal with!

Esteruelas, N. F., Malmsten, J., Bröjer, C., Grandi, G., Lindström, A., Brown, P. Swenson, Jon E., Evans, Alina L. Arnemo, Jon M. (2016). Chewing lice Trichodectes pinguis pinguis in Scandinavian brown bears (Ursus arctos). International Journal for Parasitology: Parasites and Wildlife 5: 134-138.

This post was written by Aidan McCarthy

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