Category Archives: Parasites

Friday Fellow: Pear Rust

by Piter Kehoma Boll

Beautiful and deadly, today’s fellow appears during spring as gelatinous orange projections coming out of juniper trees in Europe and North America. Its name is Gymnosporangium sabinae, commonly known as the pear rust.


The jelly-like horns of the pear rust on a juniper tree. Photo by Mark Sadowski.*

The pear rust is a basidiomycete, i.e., a fungus of the phylum Basidiomycota, therefore related to the common mushrooms, but belonging to a different class, the Puccioniomycetes.

During winter, the pear rust remains in a resting state inside branches and twigs of juniper trees. After wet days in spring, the fungus sprouts and appears as horn-like growths covered by an orange gelatinous mass, which are called telia. The telia produce wind borne spores called teliospores that can infect pear trees.


The pear rust on pear leaves. Photo by Jan Homann.

Once reaching the pear tree, the teliospores germinate and infect the leaves of the new host. The infection appears in summer as rust-colored spots on the leaves, hence the name pear rust. In heavily infected plants, the effects of the pear rust can be severe, sometimes causing the plant to lose all its leaves.

In pear trees, the fungus produce reproductive structures known as aecia. They come out from the underside of pear leaves and produce spores called aeciospores, which are able to infect new juniper trees.


The aecia coming out of the rust on a pear tree. Photo by H. Krisp.**

Due to the economic importance of pear trees to humans, the pear rust is a species of great concern. Some countries have policies intended to reduce the spread of the disease, such as preventing transportation of juniper trees from areas known to have the fungus to areas in which it is unknow. In areas where the fungus exist, the solutions to reduce the damage include the use of chemical fungicides, the removal of infected branches in juniper trees and sometimes the removal of any juniper tree around the areas where pear trees are cultivated.

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Fraiture, A.; Vanderweyen, A. (2011) Gymnosporangium sabinae: such a beautifiul disease. Scripta Botanica Belgica 11: 193–194.

Ormrod, D. J.; O’Reilly, H. J.; van der Kamp, B. J,; Borno, C. (1984) Epidemiology, cultivar susceptibility, and chemical control of Gymnosporangium fuscum in British Columbia. Canadian Journal of Plant Pahology6: 63–70.

Wikipedia. Gymnosporangium sabinae. Available at < >. Access on April 27, 2018.

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Friday Fellow: Green-Banded Broodsac

by Piter Kehoma Boll

Parasites are very speciose, and I often feel that I’m not giving enough space for them here, especially when I bring you a flatworm, which is likely the group with the largest number of parasite species. So let’s talk about one today at last.

The first parasitic flatworm I am introducing to you is Leucochloridium paradoxum, the green-banded broodsac. It is a member of the flatworm group Trematoda, commonly known as flukes and, as all flukes, it has a complex life cycle.

Adults of the green-banded broodsac live in the intestine of various passerine birds of North America and Europe. The eggs they lay reach the environment through the bird’s feces and are eventually ingested by land snails of the genus Succinea.


Adult individual of Leucochloridium paradoxum (left), an infected intermediate hose, a sail of the genus Succinea (center) and the sporocysts along the snail’s internal organs (right). Images not to scale. Extracted from

Adults of Leucochloridium paradoxum are very similar to the adults of other species of the genus Leucochloridium, the main differences being seen in the larval stages. Inside the body of the snail, the eggs hatch into the first larval stage, the miracidium, which inside the snail’s digestive system develops into the next stage, the sporocyst.

The sporocyst has the form of a long and swollen sac (the broodsac, hence the common name) that is filled with many cercariae, which are the next larval stage. The sporocyst than migrates towards the snail’s eye tentacles, invading them and turning them into a swollen, colorful and pulsating structure that resembles a caterpillar. In this stage of infection, the poor snail is most likely blind and cannot avoid light as it normally does. As a result, it becomes exposed to birds that mistake it for a juicy caterpillar, eating it eagerly.


A poor snail of the species Succinea putris with a broodsac in its left eye stalk. There is only one terrible fate for this creature. Photo by Thomas Hahmann.*

When the snail is eaten, the sporocyst burst and the several cercariae are released. In the bird’s intestine, they develop into adults and restart the nightmarish cycle.

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Rząd, I.; Hofsoe, R.; Panicz, R.; Nowakowski, J. K. (2014) Morphological and molecular characterization of adult worms of Leucochloridium paradoxum Carus, 1835 and L. perturbatum Pojmańska, 1969 (Digenea: Leucochloridiidae) from the great tit, Parus major L., 1758 and similarity with the sporocyst stages. Journal of Helminthology 88(4): 506-510. DOI: 10.1017/S0022149X13000291

Wikipedia. Leucochloridium paradoxum. Available at < >. Access on March 8, 2018.

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Friday Fellow: Large Roundworm of Pigs

by Piter Kehoma Boll

It’s time to go back to the roundworms and to the parasites once more. Probably one of the most famous roundwors is the large roundworm of humans, Ascaris lumbricoides, but today I’m going to talk about its closest relative, the large roundworm of pigs, Ascaris suum.

Found worlwide, the large roundworm of pigs, as its name implies, infects pigs. It is a large worm of the phylum Nematoda and is very similar to the large roundworm of humans, the main difference being simply that the former infects pigs and the latter infects humans.


A typical male (top) and female (bottom) of Ascaris suum. Photo by Wikimedia user VlaminckJ.*

The adult worms live in the intestine of pigs and show sexual dimorphism. Males are smaller, measuring 13–31 cm in length and have a curled posterior end. Females are larger, measuring 20–49 cm and do not have the curled posterior end. They have a light pink to whitish color and may occur in large quantities inside the host.

When sexually mature, a female can lay up to 200 thousand eggs per day and have up to 27 million eggs in its uteri. The eggs are eliminated with the pig feces and remain in the environment where the embryo starts its development. As soon as the eggs are eaten by a pigg, the eggs hatch and the larvae crawl into the walls of the large intestine and reach the bloodstream, being carried to the liver and from there to the lungs. In the lungs, they reach the alveoli and start to migrate upward toward the trachaea and are coughed up and swallowed by the pig, reaching the intestine again. There, they remain in the small intestine and complete their development into adults.

The great similarity of Ascaris suum and Ascaris lumbricoides implicate that they have a recent common ancestor which may have split into the two species after humans started to raise pigs. Eventually Ascaris suum may also infect humans and Ascaris lumbricoides may infect pigs too, but they seem to have a preference and an improved development in their “traditional” host. Molecular studies indicate that the populations of both species seem to be considerable isolated, but there have been some eventual hybridizations, suggesting that they are yet in the process of become fully separate species.

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Leles, D.; Gardner, S. L.; Reinhard, K.; Iñiguez, A.; Araujo, A. (2012) Are Ascaris lumbricoides and Ascaris suum a single species? Parasite and Vector5: 42.

Wikipedia. Ascaris suum. Available at: < >. Access on November 6, 2017.

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Friday Fellow: H. pylori

by Piter Kehoma Boll

I already introduced three species of bacteria here, all of them free-living and/or friendly little ones. But we all know that many bacteria can be a real annoyance to us humans, and so it’s time to show some of those, right?

I decided to start with one that I thought to have living inside me some time ago (but it happened that I don’t), and this is the ill-tempered Helicobacter pylori, which as usual lacks a common name, but is commonly called H. pylori for short by doctors, so that’s how I’ll call it.


Electron micrograph of a specimen of H. pylori showing the flagella.

The most common place to find the H. pylori is in the stomach. It is estimated that more than half of the human population has this bacterium living in their gastrointestinal tract, but in most cases it does not affect your life at all. However, sometimes it can mess things up.

H. pylori is a 3-µm long bacterium with the shape of a twisted rod, hence the name Helicobacter, meaning “helix rod”. It also has a set of four to six flagella at one of its ends, which make it a very motile bacterium. The twisted shape, together with the flagella, is thought to be useful for H. pylori to penetrate the mucus lining the stomach. It does so to escape from the strongly acidic environment of the stomach, always penetrating towards a less acidic place, eventually reaching the stomach epithelium and sometimes even living inside the epithelial cells.

In order to avoid even more the acids, H. pylori produces large amounts of urease, an enzyme that digest the urea in the stomach, producing ammonia, which is toxic to humans. The presence of H. pylori in the stomach may lead to inflammation as an imune response of the host, which increases the chances of the mucous membranes of the stomach and the duodenum to be harmed by the strong acids, leading to gastritis and eventually ulcers.

The association between humans and H. pylori seem to be very old, possibly as old as the human species itself, as its origin was traced back to East Africa, the cradle of Homo sapiens. This bacterium is, therefore, an old friend and foe and it will likely continue with us for many many years in the future.

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Linz, B.; Balloux, F.; Moodley, Y. et al. (2007) An African origin for the intimate association between humans and Helicobacter pyloriNature 445: 915–918.

Wikipedia. Helicobacter pylori. Available at < >. Access on August 5, 2017.

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Friday Fellow: Operculate Acrochaete

by Piter Kehoma Boll

Last week I introduced a red alga, the Irish moss. Today I’m bringing another alga, this time a green one, but this is not an ordinary green alga, but a parasite of the Irish moss! So let’s talk about Acrochaete operculata, or the operculate acrochaete as I decided to call it in English, since obviously there would be no common name for an alga parasite of another alga.

Discovered and named in 1988, the operculate acrochaete is an exclusive parasite of Chondrus crispus. The infection occurs when flagellate zoospores of the parasite settle on the outer cell wall of the Irish Moss, where they start their development and digest the cell wall, penetrating the tissues of the host. In sporophytes of the Irish moss, the operculate acrochaete digests the intercellular matrix and spreads through the frond, while in gametophytes the infections remains localized, forming papules. The damages caused by the green alga lead to secondary infections by other organisms, especially bacteria, and the infected fronds end up falling apart, completely degradated.


A frond of the host (Chondrus crispus) to the left and the parasitic Acrochaete operculata that infects its tissues to the right. Photo extracted from

As mentioned last week, the sporophytes and gametophytes of the Irish Moss have different forms of the polysaccharide carrageenan and this seems to be the reason why the parasite infects both forms differently. The sporophytes have lambda-carrageenan, which seems to increase the virulence of the parasite, while the kappa-carrageenan of the gametophyte seems to limit the green alga’s spread.

Since its discovery, the operculate acrochaete and its interaction with the Irish moss has been studied as a way to both reduce its damage on cultivated crops of the red alga and as a model to understand the relationship of plants and their pathogens.

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Bouarab, K.; Potin, P.; Weinberger, F.; Correa, J.; Kloareg, B. (2001) The Chondrus crispus-Acrochaete operculata host-pathogen association, a novel model in glycobiology and applied phycopathology. Journal of Applied Phycology 13(2): 185-193.

Correa, J. A.; McLachlan, J. L. (1993) Endophytic algae of Chondrus crispus (Rhodophyta). V. Fine structure of the infection by Acrochaete operculata (Chlorophyta). European Journal of Phycology 29(1): 33–47.

Correa, J. A.; Nielsen, R.; Grund, D. W. (1988) Endophytic algae of Chondrus crispus (Rhodophyta). II. Acrochaete heteroclada sp. nov., A. operculata sp. nov., and Phaeophila dendroides (Chlorophyta). Journal of Phycology 24: 528–539.


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Friday Fellow: B. coli

by Piter Kehoma Boll

It’s time to give more space for parasites, including human parasites! So today our fellow comes right from the stool of many mammals, including humans. Its name is Balantidium coli, or B. coli for short.

B. coli is a ciliate, i.e., a member of the phylum Ciliophora, a group of protists that have their cells covered by cilia, which are nothing more than very short and numerous flagella. Most ciliates are free-living organisms, and in fact B. coli is the only ciliate known to be harmful to humans, but not only to humans. Many other mammals are also known to host this fellow, especially pigs.


The red elongate macronucleus of B. coli makes it look like a bad guy, don’t you think? Photo extracted from

The typicall habitat of B. coli is the large intestine of mammals. The protist lives there in an active phase called trophozoite (seen in the image above) and feeds on the natural bacteria that live in the gut. When facing dehydration, which happens in the final portion of the intestine or after the organism is released with the feces, B. coli changes to an inactive phase called cyst, which is smaller than the trophozoite and covered by a thick wall. The cysts released in the environment may be ingested by a new host and reach their intestine, where they will return to the trophozoite form.


A cyst of B.coli. Photo extracted from

Symptoms of infection by B. coli, also known as balantidiasis, include explosive diarrhea every 20 minutes and, in acute infections, it may cause perforation of the colon and become a life-threatening condition.

Fortunately, infection in humans is not that common. The most affected country nowadays are the Philippines, but you may get infected anywhere. The best way to reduce the infection risks is by having good sanitary conditions and personal hygiene. However, as pigs are the most common vectors of the disease, it will likely continue to exist as long as humans raise pigs.

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Schuster, F., & Ramirez-Avila, L. (2008). Current World Status of Balantidium coli Clinical Microbiology Reviews, 21 (4), 626-638 DOI: 10.1128/CMR.00021-08

Wikipedia. Balantidium coli. Available at <;. Access on February 23, 2017.

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Friday Fellow: Cute bee fly

ResearchBlogging.orgby Piter Kehoma Boll

Recently the appearance of a new pokémon, Cutiefly, has brought a lot of attention to the real world species in which it is based. So why not bring it to Friday Fellow so that you may know a little more about this creature? Its name is Anastoechus nitidulus, which I will call here “cute bee fly”, as most people find it very cute.

The cute bee fly is indeed very cute. Photo extracted from

The cute bee fly is indeed very cute. Photo extracted from

The cute bee fly belongs to the family of flies called Bombyliidae and commonly known as bee flies. The name comes from the fact that adults usually feed on nectar and polen, just like bees, and some of them are important pollinators.

Feeding. Photo extracted from reddit, posted by usar AnanasJonas.

Feeding. Photo extracted from reddit, posted by user AnanasJonas.

Unfortunately, just as many species, the cute bee fly may be very popular among laypeople and you find a lot of nice pictures of it on the web, just as the one above. However, scientifically, very little is known about its ecology.

Nevertheless, on thing is certain: despite its cuteness, it is not such a lovely creature. Its adult life flying from flower to flower hides a dark and evil past. During their period as larvae, bee flies are predators or parasitoids, meaning that they grow up by eating another animal alive, from inside out, in something that is certainly very horrible for the poor victim.

In the case of the cute bee fly, things are not that terrible. They feed on the egg-pods of grasshoppers, especially of the genus Calliptamus, so we can say that they are parasitoids of eggs instead of adults, but then you realize that eggs have embryos, so they are actually baby-eaters!



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Brooks, A. (2012). Identification of Bombyliid Parasites and Hyperparasites of Phalaenidae of the Prairie Provinces of Canada, with Descriptions of Six Other Bombyliid Pupae (Diptera) The Canadian Entomologist, 84 (12), 357-373 DOI: 10.4039/Ent84357-12

Jazykov (Zakhvatkin), A. (2009). Parasites and Hyperparasites of the Egg-pods of injurious Locusts (Acridodea) of Turkestan Bulletin of Entomological Research, 22 (03) DOI: 10.1017/S0007485300029904

Wikipedia. Bombyliidae. Available at < >. Access on July 26, 2016.

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