Category Archives: Parasites

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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Filed under Friday Fellow, Parasites, protists

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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Filed under Entomology, Friday Fellow, Parasites, Zoology

Friday Fellow: Heartworm

by Piter Kehoma Boll

Life is not composed only by beautiful and cute creatures. Parasites form a big part of life. In fact, it is likely that there are more parasitic species than non-parasitic ones.

The heartworm (Dirofilaria immitis) is one of these not-so-cute species. A species of roundworm, it infects small mammals, especially dogs, and is spread by mosquitoes.

The name heartworm comes from the fact that this worm lives in the heart and pulmonary arteries of dogs during its adult stage. The result of the infection may be heart failure and damage on the heart and the arteries, but some infections may pass completely unnoticed, especially in sedentary dogs.

Not a pleasant view. Heartworms in a dog's heart. Photo by Alan R Walker*.

Not a pleasant view. Heartworms in a dog’s heart. Photo by Alan R Walker*.

After males and females mate in the heart of the dog, females give birth to live larvae called microfilariae. These are released in the bloodstream and await for being transfered to a bloodsucking mosquito during a bite. Over 60 species of mosquitoes are known to serve as intermediate hosts of microfilariae.

Inside the mosquito, the microfilariae grow from the larval stage L1 to the larval stage L3 and then migrate to the mosquito’s salivary glands and, once it bites another dog, they are transferred to it and develop under the skin at the site of the bite to the stage L4. Now the L4 larve migrate to the dog’s muscles and develop into the stage L5. Finally, they start to migrate through the bloodstream until they reach the heart and the pulmonary artery, where they mold into adults and the cycle is complete.

We may find such worms disgusting, but we must admit that they have a complex and amazing life.

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Wikimedia. Dirofilaria immitis. Available at: < >. Access on June 7, 2012.

Ludlam, K. W.; Jachowski, L. A.; Otto, G. G. 1970. Potential vectors of Dirofilaria imiitis. Journal of the American Veterinary Medical Association, 157: 1354-1359.

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This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

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Filed under Friday Fellow, Parasites, worms