''Balantidium coli'' is a

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

ciliate The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagellum, eukaryotic flagella, but are in general shorter and present in much larger numbers, with a ...

alveolates The alveolates (meaning "pitted like a honeycomb") are a group of protists, considered a major clade and superphylum within Eukarya. They are currently grouped with the stramenopiles and Rhizaria among the protists with tubulocristate mitochond ...

that causes the disease balantidiasis. It is the only member of the ciliate phylum known to be

pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...

ic to humans.

Morphology

''Balantidium coli'' has two developmental stages, a

trophozoite A trophozoite (G. ''trope'', nourishment + ''zoon'', animal) is the activated, feeding stage in the life cycle of certain protozoa such as malaria-causing ''Plasmodium falciparum'' and those of the '' Giardia'' group. (The complement of the trophozo ...

stage and a cyst stage. In trophozoites, the two nuclei are visible. The macronucleus is long and sausage-shaped, and the spherical micronucleus is nested next to it, often hidden by the macronucleus. The opening, known as the

peristome Peristome (from the Greek ''peri'', meaning 'around' or 'about', and ''stoma'', 'mouth') is an anatomical feature that surrounds an opening to an organ or structure. Some plants, fungi, and shelled gastropods have peristomes. In mosses In mosses, ...

, at the pointed anterior end leads to the cytostome, or the mouth. Cysts are smaller than trophozoites and are round and have a tough, heavy cyst wall made of one or two layers. Usually only the macronucleus and sometimes cilia and

contractile vacuoles A contractile vacuole (CV) is a sub-cellular structure (organelle) involved in osmoregulation. It is found predominantly in protists and in unicellular algae. It was previously known as pulsatile or pulsating vacuole. Overview The contractile ...

are visible in the cyst, however, both nuclei are present because nuclear multiplication does not occur when the organism is a cyst. Living trophozoites and cysts are yellowish or greenish in color.

Transmission

''Balantidium'' is the only ciliated protozoan known to infect humans. Balantidiasis is a

zoonotic disease A zoonosis (; plural zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen (an infectious agent, such as a bacterium, virus, parasite or prion) that has jumped from a non-human (usually a vertebrate) to a human. ...

and is acquired by humans via the feco-oral route from the normal

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County People *Jim Host (born 1937), American businessman * Michel Host ...

, the domestic pig, where it is asymptomatic. Contaminated water is the most common mechanism of transmission.

Role in disease

''Balantidium coli'' lives in the cecum and colon of humans, pigs, rats, and other mammals. It is not readily transmissible from one species of host to another because it requires a period of time to adjust to the symbiotic flora of the new host. Once it has adapted to a host species, the protozoan can become a serious pathogen, especially in humans. Trophozoites multiply and encyst due to the dehydration of feces. Infection occurs when the cysts are ingested, usually through contaminated food or water. ''B. coli'' infection in immunocompetent individuals is not unheard of, but it rarely causes serious disease of the gastrointestinal tract. It can thrive in the gastrointestinal tract as long as there is a balance between the protozoan and the host without causing dysenteric symptoms. Infection most likely occurs in people with malnutrition due to the low

stomach The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...

acidity or people with compromised immune systems. In acute disease, explosive diarrhea may occur as often as every twenty minutes. Perforation of the colon may also occur in acute infections which can lead to life-threatening situations.

Life cycle

Infection occurs when a host ingests a cyst, which usually happens during the consumption of contaminated water or food. Once the first cyst is ingested, it passes through the host's digestive system. While the cyst receives some protection from degradation by the acidic environment of the stomach through the use of its outer wall, it is likely to be destroyed at a pH lower than 5, allowing it to survive easier in the stomachs of malnourished individuals who have less stomach acid. Once the cyst reaches the small intestine, trophozoites are produced. The trophozoites then colonize the large intestine, where they live in the lumen and feed on the

intestinal flora Gut microbiota, gut microbiome, or gut flora, are the microorganisms, including bacteria, archaea, fungi, and viruses that live in the digestive tracts of animals. The gastrointestinal metagenome is the aggregate of all the genomes of the gut mi ...

. Some trophozoites invade the wall of the colon using

proteolytic enzymes Proteolysis is the breakdown of proteins into smaller polypeptides or amino acids. Uncatalysed, the hydrolysis of peptide bonds is extremely slow, taking hundreds of years. Proteolysis is typically catalysed by cellular enzymes called protease ...

and multiply, and some of them return to the lumen. In the lumen, trophozoites may disintegrate or undergo encystation. Encystation is triggered by dehydration of the intestinal contents and usually occurs in the distal large intestine, but may also occur outside of the host in feces. Now in its mature cyst form, cysts are released into the environment where they can go on to infect a new host.

Epidemiology

Balantidiasis in humans is common in the

Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...

, but it can be found anywhere in the world, especially among those that are in close contact with swine. The disease is considered to be rare and occurs in less than 1% of the human population. The disease poses a problem mostly in developing countries, where water sources may be contaminated with swine or human feces.

References

External links

* * {{DEFAULTSORT:Balantidium Coli Litostomatea Parasitic alveolates Waterborne diseases Zoonoses Species described in 1857