Sucker worms are a class of flatworms. They are classified as parasites.
What are sucking worms?
Suckworms (Trematoda) are a class of flatworms (Plathelminthes). The worms lead a parasitic lifestyle and include about 6000 different species. A typical characteristic of the sucking worms is their leaf- or roller-shaped body. In addition, the parasites have two suckers, which serve as adhesive organs. Known species of sucking worms are, for example, the couple fluke, the intestinal fluke, the lung worm and the large liver fluke. Some flukes have the ability to infect and cause disease in humans as well as pigs, cattle, dogs and cats. Most species of sucking worms are hermaphrodites. Thus, the animals have both male and female sex organs. As hermaphrodites, they have the ability to fertilize each other as well as themselves.
Occurrence, distribution and characteristics
Sucking worms are distributed almost all over the globe. They show up preferentially in the places where they find their hosts. Thus, adult sucking worms live in numerous vertebrate species. The first intermediate hosts of the sucking worm are always snails. Fish or arthropods can serve as the second host. The final host is a vertebrate species without fixed assignment. Due to its feeding habits, the sucking worm Fasciola hepatica is mostly found in end hosts such as sheep and cattle. However, it is also quite possible for it to infest humans. The length of the sucking worms varies from 0.2 to 165 millimeters. The flukes usually have a body shape that is flat and long. Sometimes it is also squat. In contrast, vein flukes and pair flukes have an almost round cross-section. The digestive tract of the sucking worms ends blind. In addition, they are equipped with specialized sensory organs. At the front end of the body the sucking worm has a mouth sucker. Furthermore, there is a ventral sucker. With their muscular suckers, most sucking worms have the ability to attach themselves to specific docking sites on the host body. Most species of sucker worms go through two larval stages of short duration. The first life stage of the sucker worm larvae is called the ciliated larva or miracidium. The miracidium has a hair coat and is indicative of the original relatives of flatworms, the tubellaria. All sucking worms represent endoparasites. Their life cycles are considered complex. Thus, in principle, the parasites require different vertebrate species for their life cycle. The host body usually excretes the sucker worm eggs in its feces. If the sucking worms live in water, they hatch miracidia (ciliated larvae). The miracidium drifts around in the water until its energy reserves are exhausted. If the ciliated larva is lucky, it finds a snail that is suitable for its further development. To penetrate the snail, the miracidium bores into its tissue. Metamorphosis results in a transformation into a brood tube. In this sporocyst, development of daughter sporocysts or redia (stablarvae) takes place by budding, and these move forward to the midgut gland of the snail. Further stablarvae develop from the stablarvae. From these, new larval forms are produced with tail larvae (cercariae). The cercariae are able to leave the host snail and seek out a new intermediate host. This is usually fish, by which they are swallowed. Sometimes the parasites cause significant changes in the behavior of the affected fish. An exception is the sucking worm family Fasciolidae. In this family, the cercariae attach themselves to aquatic plants. There they form cysts and develop into metacercariae. Through food, the metacercariae can enter the final host, which includes birds or mammals. After rupturing the enveloping cysts, the young worms usually colonize the digestive tract. However, some also penetrate into the bloodstream, lungs, or liver. Sexual maturity and mating eventually take place at these sites.
Diseases and ailments
Most sucking worms live in the tropics. Some species can infest humans and cause various diseases in them. These include primarily the couple flukes (schistosomes), which cause schistosomiasis (bilharzia) in numerous tropical countries.According to WHO estimates, more than 200 million people are infected with schistosomes. Around 120 million of those affected suffer from symptoms of the disease. In around 20 million patients, the parasite infestation even has serious consequences. Approximately 20,000 people die each year as a result of schistosomiasis. In medicine, a distinction is made between intestinal bilharzia, liver spleen bilharzia and bladder bilharzia. In the case of a sucking worm infestation of humans in water, itchy redness on the skin becomes noticeable at first. Later, the patient also suffers from fever. Afterwards, typical schistosomiasis symptoms appear, such as blood deposits on the stool or bloody urine. If the worm infestation persists for several years, connective tissue changes in the colon and severe liver dysfunction are possible. With timely treatment, however, the prognosis for schistosomiasis is generally positive. In temperate climates such as Europe, pathogenic sucking worms hardly occur in humans due to extensive hygiene measures. In wild animals and livestock, on the other hand, there are pronounced wormings. However, if the flukes enter the human body, the symptoms depend on which organ has been attacked. Thus, fluke diseases of the liver often cause symptoms such as abdominal pain, jaundice and diarrhea. Diseases caused by flukes are treated with special worming drugs (anthelmintics), which are administered once. The drugs interfere with the metabolism of the flukes and kill them, allowing them to be excreted in the stool.
