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The liver fluke is a parasitic worm that lives in the human or animal body, affecting the liver and bile ducts. The liver fluke is widespread throughout the world, it causes a disease called fascioliasis. Most often, the worm parasitizes in the body of large and small cattle, although massive and sporadic outbreaks of invasion among people are known. Data on actual morbidity vary widely. According to various sources, the total number of people infected with fascioliasis ranges from 2,5-17 million people worldwide. In Russia, the liver fluke is widespread among animals, especially in areas where there are swampy pastures. The parasite is rare in humans.
The liver fluke is a trematode with a flat leaf-shaped body, two suckers are located on its head. It is with the help of these suckers that the parasite is retained in the body of its permanent host. An adult worm can be up to 30 mm long and 12 mm wide. The stages of development of the liver fluke are as follows:
Stage marita liver fluke
Marita is the sexually mature stage of the worm, when the parasite has the ability to release eggs into the external environment. The worm is a hermaphrodite. The body of marita is shaped like a flattened leaf. The sucker mouth is at the anterior end of the body. Another sucker is on the ventral part of the body of the worm. With its help, the parasite is attached to the internal organs of the host. Marita independently reproduces eggs, as she is a hermaphrodite. These eggs are passed out with the feces. In order for the egg to continue development and pass into the larval stage, it needs to get into the water.
Larval stage of the liver fluke – miracidium
Miracidium comes out of the egg. The larva has an oval oblong shape, its body is covered with cilia. On the front of the miracidium are two eyes and excretory organs. The rear end of the body is given under the germ cells, which will later allow the parasite to multiply. With the help of cilia, miracidium is able to actively move in the water and look for an intermediate host (freshwater mollusk). After the mollusk is found, the larva takes root in its body.
Sporocyst stage of the liver fluke
Once in the body of the mollusk, the miracidium passes into the next stage – the sac-like sporocyst. Inside the sporocyst, new larvae begin to mature from germ cells. This stage of the liver fluke is called redia.
Liver fluke larva – redia
At this time, the body of the parasite lengthens, it has a pharynx, the intestines, excretory and nervous system are born. In each sporocyst of the liver fluke, there can be from 8 to 100 redia, which depends on the specific type of parasite. When the redia mature, they emerge from the sporocyst and penetrate the tissues of the mollusk. Inside each redia there are germ cells that allow the hepatic fluke to move on to the next stage.
Circaria stage of the liver fluke
At this time, the larva of the liver fluke acquires a tail and two suckers. In cercariae, the excretory system is already formed and the rudiments of the reproductive system appear. The cercariae leaves the shell of the redia, and then the body of the intermediate host, perforating it. To do this, she has a sharp stylet or a bunch of spikes. In this state, the larva can move freely in the water. It is attached to any object and remains on it in anticipation of a permanent owner. Most often, such objects are aquatic plants.
Stage of adolescaria (metatsercaria) of the hepatic fluke
This is the final larval stage of the liver fluke. In this form, the parasite is ready to penetrate the body of an animal or a person. Inside the organism of the permanent host, the metacercariae turns into marita.
The life cycle of the liver fluke is quite complicated, so most of the larvae die without turning into a sexually mature individual. The life of the parasite can be interrupted at the stage of the egg if it does not enter the water or does not find the right type of mollusk. However, the worms have not died out and continue to multiply, which is explained by compensatory mechanisms. First, they have a very well developed reproductive system. An adult marita is capable of reproducing tens of thousands of eggs. Secondly, each sporocyst contains up to 100 redia, and each redia can reproduce more than 20 cercariae. As a result, up to 200 thousand new liver flukes can appear from one parasite.
Animals become infected most often when eating grass from water meadows, or while drinking water from open stagnant reservoirs. A person will be infected only if he swallows a larva in the adolescaria stage. Other stages of the liver fluke are not dangerous for him. In order to prevent the possibility of infection, you should thoroughly wash vegetables and fruits that are consumed raw, and also do not drink water that has not undergone the necessary processing.
Once in the human or animal body, adolescaria penetrates the liver and bile ducts, attaches there and begins to reproduce. With their suckers and spines, parasites destroy the liver tissue, which leads to its increase in size, to the appearance of tubercles. This, in turn, contributes to the formation of cirrhosis. If the bile ducts are clogged, then the person develops jaundice.