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.

Bivitellobilharzia loxodontae

Blood flukes from the genus Schistosoma are found in over 77 countries, infecting at least 230 million people, and second only to malaria as the most socioeconomically crippling parasitic disease in the world. But the majority of flukes from the family Schistosomatidae do not infect humans; they parasitise other species of mammals, as well as birds. There are about 100 known species of schistosome flukes around the world. Understandably, those species from the genus Schistosoma are the most extensively studied due to their public health importance. However, there are many other blood flukes for which very little is known on even the most basic aspect of their ecology.

Photo by Thomas Breuer from here

Meet Bivitellobilharzia loxodontae; a schistosome that parasitises African forest elephants (Loxodonta cyclotis). It holds the distinction of probably being the most poorly known of all the schistosomes. The first and only adult specimens of this fluke were retrieved from an elephant that had died in an animal park in Hagenbeck, Germany. To this day, almost everything known about this parasite had come from those samples which were described in 1940. The elephant that was hosting those blood flukes was likely captured from the region now known as the Democratic Republic of Congo.

Because B. loxodontae is an endoparasite (internal parasite) of elephants, adult specimens are hard to come by as they can only be retrieved via "destructive sampling" (dissecting the circulatory system of a dead elephant). And despite extensive sampling in the area where the forest elephant resides, the snail host (where the asexual larval stages of this parasite reside) has not yet been identified. Documenting the life-cycle of these parasites is a labour-intensive and time-consuming task as it requires finding all the different larval stages and demonstrating that all those different stage do indeed belong to the same species by performing experimental infections. Performing experimental infection on an animal like an elephant is out of the question due to its large size and rarity.

Photo of B. loxodontae egg
from the paper

With the advent of molecular techniques, it is now possible to confirm the identity of parasites at different stages of their life cycle without experimental infection (even though experimental infections are still useful for working out other aspects of a parasite's ecology). This can be done by sequencing specific sections of DNA which can serve as markers that identify the species and differentiate it from other parasites which might look similar. In the paper we are featuring today, the researchers extracted DNA from B. loxodontae eggs that were retrieved from samples of elephant dung in order to work out how this blood fluke fits into the schistosome family tree.

Their analyses showed that out of all the schistosome blood flukes, it is most closely related to Bivitellobilharzia nairi -  a species known from the Asian elephant (Elephas maximus). Taxonomically, the genus Bivitellobilharzia sits near the base of a branch within the schistosome family that contains mammal-infecting species (including those species from the Schistosoma genus). The pattern of branches in the schistosome family indicates that at some point in the past, the mammal-infecting group evolved in a divergent direction (in terms of host use) to the rest of the family, which is composed of species that infect birds. This raises intriguing questions about the deep evolutionary history of this group of parasites.

Reference:
Brant SV, Pomajbíková K, Modry D, Petrželková KJ, Todd A, Loker ES. (2013) Molecular phylogenetics of the elephant schistosome Bivitellobilharzia loxodontae (Trematoda: Schistosomatidae) from the Central African Republic. Journal of Helminthology 87: 102-107.

November 29 - Equinurbia blakei

The scanning electron microscope has allowed us to see the awesome symmetry of some nematodes up close and personal. Equinurbia blakei is an intestinal parasite of African elephants and one of a group called “large strongyles.” This group is characterized by complicated mouthparts called the corona radiata (radial crown) seen here. The four structures outside the crown are called amphids and are sensory organs. Large strongyles are characteristic of ruminants and some hosts, such as zebras, can harbor up to 20 species and over a million total worms per animal.

Contributed by Mike Kinsella.

April 17 - Haematomyzus elephantis

The same species of louse, known as Haematomyzus elephantis, is found on both Asian and African elephants. Although it seems like a bizarre coincidence that this parasite should have a long “proboscis” like its host, the length of its mouthparts is an adaptation to penetrate the thick skin of the elephant. And although the ”proboscis” might also look like a giant straw to suck blood, these are not sucking lice (Anoplura) but chewing lice (Mallophaga), which feed on the epidermis. They are so highly evolved that an entire suborder (Rhynchophthirina) was created for only 3 species (the other 2 are found on warthogs).

Contributed by Mike Kinsella.