Nerdy Science Blog

The scientific name for flatworms is Platyhelminthes (platy- is Greek and it means flat, while helminth- means worm). In basic zoology, the Platyhelminthes can be divided into Turbellaria (non-parasitic animals) and 3 other parasitic groups – the Cestoda, Trematoda and Monogenea. Even thou four of them belong to the same phylum, in the medical world, only 2 out of 3 of the parasitic group could play the role of being parasitic in the human body. They are the Cestoda and Trematoda. Monogeneas in the other hand are mostly parasites which require a host, in most of the cases being fish, amphibians or reptiles.

Cestodes (tapeworms) and Trematodes (flukes) have very complex life-cycles but generally, it could be divided into few stages. In the mature stages, these flatworms live as parasites in the digestive systems of vertebrates until they are mature enough to release gravid ‘eggs’ or part of their body (segment). These eggs or segments would then be released to the outside world together with the feces of the definitive host. Another person could be infected by such parasites if they consumed undercooked protein of infected fish or pork. Such parasites are generally transmitted via the oral-fecal route.

The Platyhelminthes are bilaterally symmetrical animals. The have a distinct top, head and tail ends.

The Cestodes have a very distinct head and body structure. The Cestode’s head (scientifically called the Scolex) enables the parasite to attach itself to the intestine of its definitive host. This is achieved by the existence of sucking grooves around the head which function like suction cups. This would prevent them from being ‘flushed out’ by the peristalsis of the intestines. Its long body is segmented, and these segments are known as proglottids. The whole strip of segments resembles a tape, which gave them the name “tapeworm”. The mature proglottids are released by the tapeworm and later on mixed together with the feces while they leave the host. The genesis of such infestation is by oral-fecal route. Some of the well known tapeworm parasites are Diphyllobothrium latum. A person is infected through the ingestion of infected fishes. Another popular example is the Taenia solium, whose eggs and larvae could be found in fecal-contaminated water and pork. Taenia solium can cause a serious disease called the neurocysticercosis where the cysticerci are found in the brain. Taenia Saginata is yet another example of tapeworm where a person is infected by ingesting undercooked beef.

The Trematodes usually infect mollusks as the first host in its life cycle. Eggs are shed with the definitive host’s feces. If the eggs are released into water, it will releases free-swimming larval forms which could infect other intermediate host. The flukes can be divided into 2 groups – the tissue flukes, which infect the lungs, bile ducts and other biological tissues. Examples of tissue flukes include Paragonimus westermani, Clonorchis sinensis and Fasciola hepatica. The other group is called the blood flukes. They inhabit the blood in part of their life cycle and one of the examples is Schistosoma.

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