Hymenolepis diminuta, Also known as rat appointment worm, it is a species of tapeworm or tapeworm belonging to the class Cestoda, of the phylum Platyhelminthes. It is an endoparasite of rats and mice, and on certain occasions it can also affect human health, producing a clinical condition known as hymenolepiasis..
Flatworms, better known as "flatworms", are a group of free-living, parasitic invertebrate animals. This group is made up of more than 20,000 species, which is why it is said that it harbors organisms of very different body shapes and habits.
This phylum is composed of 4 classes: the Turbellaria class (mainly free-living organisms), and the Monogenea, Trematoda and Cestoda classes, all made up of parasitic species..
The Cestoda class is divided into two subclasses: Cestodaria and Eucestoda. The Cestodaria class comprises a group of little-known flatworms that parasitize some fish and turtles, while the Eucestoda class includes well-known parasitic species of vertebrates, with complex life cycles..
To the subclass Eucestoda of the class Cestoda belong, among others, the genera Hymenolepis Y Taenia, whose species usually affect the health of humans and other mammals related to this.
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- Tiny H. is a species of parasitic invertebrate belonging to the class Cestoda, of the group of flatworms (phylum Platyhelminthes).
- From the above it is understood, then, that it is an organism composed of eukaryotic animal cells and that it is heterotrophic, since it feeds on carbon and energy contained in sources other than itself (it does not produce its own food).
- It is a strict parasite, which means that it cannot live freely without parasitizing another animal, i.e. you don't get him like a free-living worm.
- It mainly affects rodents such as rats and mice, although it can also parasitize humans, contributing to a clinical condition called hymenolepiasis, usually asymptomatic, but which can present diarrhea and abdominal pain, among other symptoms..
- Its geographical distribution includes all the temperate zones of planet earth, which is why it is considered a cosmopolitan species.
- It normally inhabits the gut of its host rodents, but can also be found in humans and canids (dogs).
- It does not have a digestive tract, so it absorbs the nutrients it needs to live through the integument that surrounds its body. Said integument is covered by a series of specialized microvilli that increase the absorption surface and whose membrane is covered by a glycocalyx rich in carbohydrates that perform essential functions for absorption..
- Its life cycle is digenetic, which implies that it needs an intermediate host for the development of its juvenile stage, generally an arthropod, which later functions as a "vector", since its definitive hosts are contaminated when feeding on this.
The adult body of Tiny H., as well as that of the other members of the Eucestoda subclass, it has three well-defined regions:
- The scolex, which is the organ of fixation thanks to which they are established in the intestine of their host. It usually has suction cups and / or hooks, which are those that fulfill the function of holding, and it is located in the anterior area of the body (the head).
- The neck, a short region located immediately after the scolex.
- The strobilus, an elongated, segmented segment that continues past the neck and is made up of individual “pieces” called proglottids. Each proglottid arises from a germinal region located in the neck, displacing the “mature” proglottids towards the posterior region of the body; each proglottid contains both female and male sex organs.
Adult individuals can measure between 20 and 90 cm in length. Its body is usually cylindrical and elongated, with 4 suction cups in the scolex region and without hooks..
Their eggs are usually slightly oval, with a size that ranges between 60 and 80 microns. They have striated outer membranes and a very thin inner membrane. The larval form included in the interior of such eggs has 6 hooks.
Hymenolepis diminuta has a digenetic life cycle, comprising an intermediate arthropod and a host mammal, usually a rodent such as a rat or mouse, cases of infected humans have rarely been reported.
1- The eggs of this parasite are released with the feces of the host, either a rodent, a human being or a canid. These mature eggs can be ingested by an intermediate arthropod host or its larvae, generally of the genus Tribolium or Tenebrio (grain beetles).
2- Inside the intestinal tract of the arthropod, the oncospheres (larvae of Tiny H. contained in eggs when consumed by the intermediate host) are released from the eggs and penetrate the intestinal walls of the host.
3- Once they penetrate the intestinal walls, these larvae develop into cysticercoid larvae, that persist during arthropod metamorphosis into adulthood.
4- The definitive hosts (rats and mice) are infected with Tiny H. once they ingest the intermediate host that is infected with the cysticercoid larvae. This ingestion occurs since both organisms can frequent the same environment, such as, for example, a grain or flour warehouse. Humans can be accidentally infected by ingesting arthropods in precooked cereals or other foods, as well as in the environment.
5- When this occurs and the intermediate host tissue is digested, the cysticercoid larvae are released into the stomach and small intestine of the mammal..
6- Shortly after this release, the larvae "evert" their scolex (remove it from within), which allows the parasite to be attached to the wall of the intestine..
7- The parasite matures within the next 20 days, reaching an average of 30 cm in length, but being able to measure more than 80.
8- The eggs are released into the small intestine from gravid (mature) proglottids, which disintegrate and release adult worms. Each worm can produce, on average, 250,000 eggs per day, however, its survival rate is very low..
9- The cycle begins again when the mammal expels the eggs with the feces, releasing them to the environment where they can be consumed by another intermediate arthropod.
The hymenolepiasis is the clinical condition caused by infection with parasites Tiny H. and H. nana. This is usually asymptomatic, however, the most acute infections in humans have been shown to cause:
- Weakness.
- Headache.
- Anorexy.
- Abdominal pain.
- Diarrhea.
- Small intestine irritation.
- Enteritis.
- Anal itching.
Its diagnosis is usually made by examining the stool under a microscope, in search of the characteristic eggs..
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