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Research shows that 80% of people in Poland are hosts of at least one parasitic worm. Every seventh Pole has a human roundworm, and every twelfth – tapeworm. Undesirable tenants usually settle with the owners of dogs and cats.

Flatworms

Flatworms have elongated, wormlike body with a head barely distinguished from the body. They are bilaterally symmetricalbilateral symmetrybilaterally symmetrical and strongly flattened dorsoventrally. Among the flatworms, there may be species that are free‑living, such as a planarian, which is a predator that lives in fresh waters. The vast majority of flatworms representatives are internal parasitesinternal parasiteinternal parasites of animals, including humans. A parasite is an organism that uses the body of another organism, the so‑called hosthosthost, as a living environment and a source of nutrition – it feeds on the food the host has digested. Being inside the host's body, it poisons the host with its excretory products. When parasites occur in large quantities, they can cause devastation and even death of the host. An example of internal parasites are tapeworms.

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Fotografia przedstawia wypławka białego (planarian) żyjącego w wodach słodkich. Płaziniec ma podłużny kształt i jasny, beżowy kolor. Część głowowa jest skierowana ukosem w prawo. Znajdują się na niej dwa czarne oczka. To wypławek biały. Prowadzi wolny tryb życia.

Tapeworms – parasitic worms

We currently know over 3 thousand species of tapeworms. All without exception live at the expense of other organisms in their interiors (at least periodically). They are perfectly adapted to the parasitic mode of life. At the front of the tapeworm body, on the scolex, there are clasping organs: bothridium (suckers) or hooks, or both. With them, the tapeworm anchors in the host's intestine. Just behind the scolex is a short section called neck. Its task is to produce proglottids, the essential elements of building the body of a flatworm. The further from the neck, the older the proglottids are. Mature proglottids are filled with eggs. Thanks to the dorsoventral flattening of the body, even a ten‑meter tapeworm can be housed in the host's intestine.

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Ilustracja przedstawia trzy schematyczne rysunki tasiemców w kolorze beżowym. Z lewej przednia część ciała tasiemca nieuzbrojonego, w środku uzbrojonego, po prawej fragment ciała tasiemca uzbrojonego ze wskazaniem na dojrzałe człony. Poszczególne części ciała tasiemców są podpisane ze wskazaniem podobieństw i różnicy- tasiemiec uzbrojony posiada na czubku główki. Na ilustracji sa opisy: sucker, head, neck, immature proglottids, hook, mature proglottids.

The tapeworms do not have a digestive system or a mouth. They do not need them because they are immersed in the nutrition filling the intestine and absorb nutrients with the entire surface of their body. They do not have respiratory organs, because they live in an oxygen‑poor environment, and their life energy comes mainly from anaerobic respiration. They are protected against the effects of digestive fluids by a thick cuticle.

Life cycle of flatworms

Flatworms are most commonly hermaphroditeshermaphroditehermaphrodites – animals of both sexes that produce both ovum and sperm. They usually undergo complex development in which the larval forms occur. A few hosts are needed for the development. LarvaelarvaLarvae live inside intermediate hosts, and adults in the body definitive host.

In the case of a pork tapeworm and a beef tapeworm, the definitive host is a human. The intermediate hosts for a pork tapeworm is – a pig, and for a beef tapeworm – a cow. Fertilization of tapeworm eggs occurs in the mature proglottids of the tapeworm that lives inside the human body. After detaching themselves from the rest of the tapeworm’s body, these proglottids escape to the external environment with the faeces of the definitive host. The intermediate host is infected by ingesting contaminated water or grass. Inside the host's body, a larva hatches from the egg, and goes from the intestine to the blood vessels, then flows in them to the muscles, where it settles, transforming into a cysticercuscysticercuscysticercus. It is a bubble with a diameter of a few millimeters, filled with the liquid in which the tapeworm’s scolex is located. A human gets infected by eating raw or undercooked meat containing cysticercus. In the human intestine, the cysticercus’ vesicular walls are digested, and the tapeworm’s scolex attaches itself to the intestinal wall and transforms into an adult tapeworm, adding further proglottids. Soon they are able to produce new eggs.

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Ilustracja z lewej przedstawia cykl rozwojowy tasiemca uzbrojonego. Rysunki rozmieszczono na błękitnym pierścieniu. Strzałki wskazują kolejne stadia rozwojowe tasiemca u jego żywicieli. Na ilustracji sa opisy: (zaczynając od jaja) Egg after leaving the proglottids, Indirect host – pig, Larvae that hatched from an egg in the body of an indirect host goes to its muscles, Young form of a tapeworm in pig’s muscle, Meat infected with young forms of tapeworm, Final host – human, Tapeworm developing from young tapeworm, Adult tapeworm in human intestine, Adult segment of a tapeworm leaving host’s body with faeces.

Conclusion

• Flatworms are worms with elongated, flattened dorsoventrally, segmented or non‑segmented body. These include internal animal parasites (tapeworms) and free‑living species.

• Flatworms undergo a complex development with a change of host. Larvae live inside the body of an intermediate host, and adult forms of parasites live in the definitive host.

• Adaptations of internal parasites to their mode of life consist, among others, in a very high fertility, reduction of sensory organs, immunity to digestive fluids, the ability to respirate anaerobically.

Keywords

tapeworm, paraside, host

Glossary