"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

June 10, 2020

Parorchites zederi

Today, we are featuring a guest post from Marie Defraigne - she is an MSc student on the IMBRSea programme, and is currently working (albeit remotely) with Dr. Katie O’Dwyer at the Galway-Mayo Institute of Technology in Ireland, during her professional practice placement. This post is about a tapeworm which is commonly found among penguins of the Antarctic sea.  

Antarctica can be considered as a continent of extremes. It is so extreme that species like mosquitoes, which are found everywhere in the world, cannot survive in this bitter cold wilderness. However, there are some creatures that can persist in the Antarctic ecosystem. The most famous of these are the penguins. Penguins are a group of seabirds belonging to the family Spheniscidae, and there are many species within this family that share the same parasite: Parorchites zederi, a species of Cestoda, or tapeworm.

This parasite can mainly be found in Gentoo PenguinsChinstrap PenguinsAdélie penguin and Emperor Penguins. The life cycle of the parasite involves multiple host animals, with krill being a known intermediate host. Since krill is an important part of the penguins’ diet, the parasite can use those crustaceans as a way of reaching their penguin hosts.

Macroscopic lesions on intestinal wall in penguins infected with Parorchites zederi, Antarctic Peninsula, 2006-2008.
(a) Intestine of adult Gentoo Penguin (Pygoscelis papua) with irregular raised nodules. (b) Heavy infection of tapeworms.
Photos from Figure 1 of Martin et al. (2016)
Tapeworm-infected penguins can end up with swellings that can be seen from the outside of the intestine, and the heaviest infections can produce yellowish-white nodules. This is a clear sign that this tapeworm negatively affects the health of the penguin. When looking more closely at the tissue, inflammation is visible with increased lymphocytes and macrophages, which are white blood cells, that form an integral part of the immune system. The presence of this tapeworm results in tissue damage and bleeding in the gut of infected penguins.

Not only do these changes lead to a reduction of normal gut functions, but the afflicted penguin probably has to endure a lot of pain when they have to digest their food in an already damaged intestine. Moreover, bacteria responsible for diarrhoea often find a cosy home in some of the tapeworm-induced lesions. No surprise then that Parorchites zederi, along with other helminths, is responsible for about 6% loss of body mass in Antarctic penguins. Losing weight is very risky business in Antarctica where insulation against the cold temperatures is vital.

Nonetheless, this tapeworm is quite common among Antarctic penguins. In some colonies of Gentoo Penguins,  parasite prevalence can even reach 100%. Given its ubiquity and the effect this parasite can have on penguin health, it is important to monitor their prevalence. Since infections with gastrointestinal parasites are closely related to foraging habits, changes in the host’s diet owing to climate change or anthropogenic impacts can lead to changes in parasite prevalence in Antarctic penguins.

In recent years there has been a decrease in sea ice cover, and because of this phenomenon, the amount of Antarctic krill has also decreased. Less krill means a lower prevalence of the tapeworms, but on the other hand it also means less food for the penguins. In this way, P. zederi can tell us more about how the Antarctic ecosystem is changing, while these penguins are faced with a constant challenge of feeding on krill and managing these problematic parasite infections.


María A Martín, Juana M Ortiz, Juan Seva, Virginia Vidal, Francisco Valera, Jesús Benzal, José J Cuervo, Carlos de la Cruz, Josabel Belliure, Ana M Martínez, Julia I Díaz, Miguel Motas, Silvia Jerez, Verónica L D'Amico, Andrés Barbosa (2016) Mode of attachment and pathology caused by Parorchites zederi in three species of penguins: Pygoscelis papuaPygoscelis adeliae, and Pygoscelis antarctica in Antarctica. Journal of Wildlife Diseases 52: 568-575.

S. Kleinertz, S. Christmann, L. M. R. Silva, J. Hirzmann, C. Hermosilla, A. Taubert (2014) Gastrointestinal parasite fauna of Emperor Penguins (Aptenodytes forsteri) at the Atka Bay, Antarctica. Parasitology Research 113: 4133–4139.

Simeon L. Hill, Tony Phillips and Angus Atkinson (2013) Potential climate change effects on the habitat of Antarctic Krill in the Weddell quadrant of the Southern Ocean. PLoS One 8: e72246.

post written by Marie Defraigne