Our body is home to many other living beings. And if the lactobacilli that live in our small intestine benefit a person (they participate in the breakdown of complex proteins and even synthesize some vitamins for us), then other organisms may become completely undesirable neighbors. It is to them that digenetic flukes belong, but simply one of the varieties of flatworms. Many of them cause quite dangerous diseases - trematodosis, which can even lead to death. Digenetic flukes, as parasites of humans and domestic animals, will be discussed in this article.
Systematic position
The class of digenetic flukes (Digenea) has about 7 thousand species and belongs to the type of flatworms (Plathelminthes). In some classifications, they belong to one of the subclasses of flukes or trematodes.(Trematoda):
- Monogenic flukes (Monogenea) are mainly external parasites of cold-blooded fish, amphibians and reptiles.
- Aspidogastrei (Aspidogastrea) - external or internal parasites of molluscs.
These flatworms, though parasitic, develop without changing hosts.
And, in fact, digenetic flukes are internal parasites (endoparasites) of warm-blooded animals and humans, which are their final hosts. That is, an organism in which the parasite reproduces sexually
Endoparasites and their hosts
The class of digenetic flukes includes blood, liver and lung obligate (mandatory) parasites. All of them have complex developmental cycles with a stage that develops in the intermediate host and an obligatory development in the definitive host.
A distinctive feature of the structure of digenetic flukes is a flat leaf-shaped body and the presence of 2 or 3 suckers, with which the sexually mature parasite attaches to the host tissues. The sizes of parasites vary from microscopic to 30 millimeters. Of the more than 4 thousand known species of digenetic flukes, about 40 species are parasites, the final host of which can be domestic animals and humans.
Morphology and physiology
The structural features of digenetic flukes are associated with their parasitic way of life. For a sexually mature individual, the following features of the body structure are characteristic:
- Like all flatworms, they havethere is no body cavity. The outer covers have a complex structure and are called tegument. It contains substances that prevent the host's gastric juice from affecting the parasite.
- The digestive system begins with the mouth, where the circular muscles - suckers - are located. Through the pharynx, food enters the stomach, usually branched into 2 parts. No anal opening.
- These cavity parasites do not have respiratory organs and lead an anaerobic lifestyle. This feature of the structure of digenetic flukes is associated with their endoparasitism, although the larval stages of some have organs that provide oxygen.
- Excretion of metabolic products occurs through ciliated cells and ends with holes on the surface of the body.
- The nervous system and sense organs are not developed or are poorly developed.
- Mature individuals are more often hermaphrodites, although there are also separate-sex representatives. The reproductive system is one ovary and two testes.
Of course, this characteristic of digenetic flukes briefly outlines the general system of their organization.
Complex life cycle
In the cycle of development of digenetic flukes there is a change of owners. Intermediate host - more often molluscs, in the body of which the larva (miracidium with cilia) develops and grows. In the body of the final host, the reproduction of digenetic flukes occurs sexually. Fertilization can be both cross-fertilization and self-fertilization incase of a hermaphroditic adult.
A sexually mature parasite lays hundreds of thousands of eggs that fall into a pond or onto land. Miracidium emerges from the egg, the task of which is to enter the body of the intermediate host. Infection of the final host occurs by eating infected animals (mollusks or freshwater crustaceans).
Liver flukes
These endoparasites live in the liver and bile ducts. From this group, 3 types of digenetic flukes deserve characteristics:
- Hepatic fluke (Fasciola hepatica) - causes the human disease fascilliasis, characterized by hepatic colic. Adult parasites are hermaphrodites, with a fleshy leaf-shaped body, length - up to 3 cm, width - 1.3 cm. Eggs from the liver through the bile ducts enter the intestine and then into the environment. Once in a fresh pond, miracidium comes out of the egg, which is introduced into the body of the snail. After several transformations, the body of the snail leaves the tailed larva - circaria, which turns into a cyst (adolescarium - a fixed form attached to algae) and is able to maintain its viability for a long time. Humans and animals become infected by drinking water with adolescaria or eating grass with them.
- Chinese liver fluke (Clonorchis sinensis) - causes clonorchiasis with symptoms similar to fascilliasis. The life cycle of this parasite is similar to the liver fluke, but there are two intermediate hosts - a snail and a fish, in the body of which the cercariae turns into a cyst. Humans and animals are infectedby eating infected fish.
- Cat fluke (Opisthorchis felineus) - causes the disease opisthorchiasis. Two-thirds of cases of infection with this parasite are among the inhabitants of Russia. That is why we will give more detailed information about these trematodes.
Inhabitant of Siberian rivers
The cat fluke is also called the Siberian fluke, since the problem of opisthorchiasis is especially relevant for Western and Eastern Siberia and the Dnieper region. This liver parasite can live in the pancreas and liver of cats, dogs and humans, which become the definitive hosts. In the life cycle of the cat's fluke, there are two intermediate hosts - snails and fish (carp, crucian carp, roach, tench, chebak, bream, asp). The life cycle and stages of development are similar to all liver flukes.
Infection of a person occurs when eating low-s alted, insufficiently thermally processed fish. In addition, when using a knife, cutting boards when cleaning and cutting river fish, cercariae remain on objects and can be brought onto other food products and serve as a source of infection. Surprisingly, this adult parasite can live up to 15-25 years.
Blood Flukes
These parasites are called schistosomes and cause the disease schistosomiasis. Representatives of digenetic flukes that parasitize in the bloodstream:
- Schistosoma haematobium and Schistosoma mansoni are common in Africa.
- Schistosomajaponicum - common in Japan, Taiwan and the Philippines.
Intermediate host - snails. Cercariae penetrate the skin into the bloodstream of the main host, migrate to the veins of the abdominal cavity, where dioecious parasites reproduce sexually, and lay eggs either in the intestines (Munson and Katayam's disease) or in the bladder (Egyptian hematuria).
Lung flukes
These are representatives of the genus Paragonimus, and diseases are paragonimiasis. Pathogens more than 10 species that are found in the Far East, China, the Philippines, Africa and Central and South America.
There are two intermediate hosts - mollusk and crustaceans (crayfish and crabs). The definitive host is warm-blooded animals and humans that have eaten infected crustaceans. In the body of the final host, trematodes are localized in the bronchi, where they form fibrous capsules. They can migrate to the lungs and even the brain.
Biological resistance of trematodes
Such complex life cycles lead to mass death of larvae. In addition, a clear selectivity in the choice of an intermediate host, and sometimes two, also does not contribute to the biological progress of the species. However, the narrow specialization and degradation of some vital functions, the long-term stability of the larval stages and cysts in the external environment, and, in most cases, the rather long life span of the parasite, have supported the evolution of trematodes for millions of years. In addition, an adult fluke produces hundreds of thousands of eggs. It is this high fecundity that keeps these parasites asspecies.
Symptomatic of trematode infection
The body of the main host reacts to infection with parasites by intoxication to poisons secreted by worms and allergic reactions to their toxins. It is worth visiting a doctor if at least one of the following symptoms appears:
- General loss of strength, weakness and drowsiness without visible physical exertion.
- Increase in body temperature over a long period.
- The appearance of allergic reactions - hives or itching.
- Liver, spleen enlargement and abdominal pain.
- Prolonged gastrointestinal disorders.
- Yellow skin and weight loss.
The incubation period for most fluke infections is 90-120 days from the moment of infection. And it is precisely such a period that needs to be analyzed to identify ways of infection with parasites.
Diagnosis and treatment of trematodosis
The main diagnostic method is the study of feces for the presence of trematode eggs. In addition, a general biochemical blood test for the presence of liver enzymes can be performed. For the diagnosis of pulmonary flukes, an x-ray of the lungs and sputum analysis are performed. If there is a suspicion of schistomiasis, a urinalysis is prescribed, where the type of fluke is diagnosed by the identified eggs.
Timely treatment will prevent the development of chronic forms of helminthiases. In treatment, the main direction is the use of antiparasitic drugs, depending on the type of pathogen. Used in opisthorchiasis"Praziquantel", "Cesol", "Dronit". With clonorchiasis - "Akrikhin". For the treatment of fascilliasis, "Chloxil" is used, and for paragonimiasis - "Biltricid".
After deworming, restorative and rehabilitation therapy is required, depending on the degree and localization of the affected organs. However, it is worth remembering that medicines should be selected exclusively by a doctor. Self-treatment in this case can not only not give a result, but also lead to the most negative consequences. Trematodes are dangerous parasites, and it is important to detect their presence in time and start timely and adequate treatment.
What traditional medicine advises
In folk practice, there are several recipes for dealing with trematodes. But it is necessary to approach their use with caution, since most of them are based on natural poisons, which, if used carelessly, can lead to poisoning. In addition, before using folk remedies, you should consult a doctor.
To get rid of these parasites, traditional medicine advises taking wormwood in the form of a tincture, which is sold in pharmacies. It should be taken 3 times a day for a teaspoon. Combine with laxatives.
Another effective remedy is dry coriander seeds. They are taken for 8 days according to the scheme - 0.5 grams on the first day, 1 gram on the second, and 1.5 grams on the remaining days. Dried black carnation flowers can also be taken in the same way.
