"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

July 10, 2017

Anoplocephala manubriata

Tapeworms are a very diverse group of parasitic worms. There are about 6000 described species and they infect a wide range of different vertebrate animals including fish, amphibians, mammals, reptiles, and birds. But even though there are so many different tapeworm species, the one thing they all have in common is that the adult worm lives in the intestine of their vertebrate host. So it would be no surprise that a large animal like an elephant would be host to tapeworms, and the species that is featured in the study that we will be covering in this blog post is Anoplocephala manubriata.

Top left: Adult Anocepgala manubriata tapeworm
Top right, bottom left: close-up of scolex and suckers
Bottom right: tapeworm egg containing oncosphere
Photo from Fig. 1 and 3 of the paper
Despite being an elephant parasite, these tapeworms are not as big as you might think. Many people think that big host means big parasites, and while some parasites in large animals can reach massive sizes, but that is not always the case. Instead of being infected by big parasites, many large animals are often host to parasites that are not much bigger than related species infecting smaller hosts.

For example, the Great White Shark is infected by a species of tiny tapeworm which measures just a few millimetres long, but what they lack in size they make up for in numbers, and a single shark can be infected by thousands of them. While A. manubriata grows to a respectable size for a tapeworm (4.6 cm–7.4 cm long and 0.7 cm to 1.8 cm wide), it is nowhere near the size of the infamous broad fish tapeworm which can reach the alarming length of over 10 metres long.

The tapeworms described in this study were retrieved from a young male elephant that died at the Udawalawe Elephant Transit Home in Sri Lanka. Anoplocephala manubriata has very muscular suckers on its scolex which allows it to keep a firm grip on the host intestinal wall. But this is not so great for the elephant - the suction from the tapeworms' suckers essentially end up leaving hickeys on the elephant's intestinal mucosa, which is not a particularly healthy place for an elephant to get love bites, especially if they have been left there by a bunch of tapeworms. Indeed, the elephant that was necropsied in this study was found to have multiple lesions and ulcers on the gut lining as a result of these parasitic love bites. This tapeworm seems to be far more common among younger elephants than adults, possibly because older elephants have more developed immune systems, and have build up some kind of resistant towards these parasites.

Tapeworms have complex life-cycles, and before the adult worm ends up in the intestine of the final host, they have to first develop as larval stages in smaller animals - usually an invertebrate, in some case a small vertebrate animal - and these small animals are usually the prey species of the final host. That is why the final host for many species of tapeworms are often predatory animals or at least animals that include smaller animals in their diet.  But what about elephants though? They are not usually known for eating bugs or other small animals, and the other tapeworms in the Anoplocephala genus are parasites that infect horses, zebras, and rhinoceros - all herbivorous mammals. So how does A. manubriata finds its way into these giant herbivorous animals?

A previous study found that A. manubriata actually uses orbatid mites as an intermediate host. Orbatid mites are minuscule arachnids that live among soil and litters - they are very tiny, and most species are less than one millimetre long. But being so tiny means that the elephant can easily swallow them inadvertently along with their usual fodder. Branches and leaves that have been in contact with soil can inadvertently pick up some of these tiny mites, and at least a few of those would be infected with  A. manubriata larvae. But there is also another way through which elephant can end up with A. manubriata. Elephants that have gastrointestinal problems also have a habit of eating dirt, possibly as a way of self-medication, as seen in other animal. However, while trying to cure themselves of one ill, they end up ingesting soil mites and inflicting another different ill upon themselves.

Like many parasites, A. manubriata is a key part of the ecosystem, and the life-cycle of this tapeworm, which involves both the elephants and soil mites, reveals the hidden ecological connection between one of the planet's largest living land animal and one of its smallest.

Reference:
Perera, K. U. E., Wickramasinghe, S., Perera, B. V. P., Bandara, K. B. A., & Rajapakse, R. P. V. J. (2017). Redescription and molecular characterization of Anoplocephala manubriata, Railliet et al., 1914 (Cestoda: Anoplocephalidae) from a Sri Lankan wild elephant (Elephas maximus). Parasitology International 66: 279-286.

4 comments:

  1. How long can a tapeworm live inside an elephant before the elephant shows signs of sickness?

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    1. It's more about how many parasites there are rather than how long they have been there. Being infected with parasites does not equate sickness regardless of during - most wild animals are running around perfectly fine while loaded with parasites all the time, it's more a matter of if they have too many.

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  2. Above you stated that older elephants may develop a resistance to the parasite, how does the immune system develop this immunity? Is it just like any other pathogen?

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