Metagonimosis
Last reviewed: 23.04.2024
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One of the varieties of helminths affecting the human small intestine is the flat worm metagonimus, which is part of the class of parasites-flukes (trematodes).
Epidemiology
It is distributed as an endemic or potentially endemic helminth in almost two dozen countries, primarily East Asia (China, Japan, Korea, Indonesia), as well as the Balkans, Spain and the Far East.
Outside the endemic areas, the meta-antimus can be infected by eating insufficiently thermally processed contaminated fish imported from these regions.
[Causes of the metagonimus
All species of this parasite (M. Yokagawai, M. Takahashi, M. Miyatai, M. Ovatus, Heterophyes yokogawai, etc.) were discovered by Japanese and Korean researchers at approximately the same time (in 1912-1932) and are identical in their morphology, size (with minor fluctuations), life cycle and even geographic distribution of intermediate hosts. Therefore, in the International Code of Zoological Nomenclature (ICZN) they are recognized as synonyms, and the main species name is Metagonimus yokogawai (metagonimus yokogawa).
Pathogenesis
Metagonimus refers to biogelmints, that is, their life cycle requires the presence of an intermediate host, and this parasite has two. The first of them are freshwater gastropods - snails of such species as Semisucospira libertine, Scoreana, Tarebia lateritia and Thiara granifera, which live from Madagascar to Hawaii, including in most countries of Southeast Asia.
The second intermediate host is freshwater fish (trout, carp, crucian carp, etc.), and the final host (in the intestine of which the parasite ripens to the state of a mature individual) is a person, as well as various predators and birds that feed on fish. The incubation period is about two weeks, while infestations in the metacercaria stage may persist in the small intestine for more than a year.
The structure of the metagonimus depends on the stage of its life cycle: the egg - miracidia - sporocyst - redia - cercaria - metacercaria - adult (mature) worm.
The adult metagonimus has an elongated body in the form of a leaf (like most trematodes) 1-2.5 mm long and 0.4-0.75 mm wide. The body is filled with the parenchyma and is covered with a protective layer - a syncytial tegument performing secretory and absorbing functions (the worm absorbs nutrients all over its surface). To the intestinal mucosa, the parasite is attached by suckers - the abdominal (deviated to the right of the middle line) and the oral (in the cranial region). A pair of ganglia in front of the body and sensory receptors serve as a worm for the brain and nervous system.
This parasite is a haemafrodite, that is, it reproduces itself by internal fertilization, for which it has ovaries, testes and an uterus filled with eggs, which is the largest organ of the worm.
Settled in the intestine of the main host of the egg (26-28 microns in length and 15-17 micrometers wide) have a solid transparent shell of yellow-brown color. The eggs have their own "hatch" in the form of a clear line of splitting between the body and the lid, which facilitates the release of the first larval stage - miracidia. And this happens when the eggs are outside the host's body and enter the water along with the excrement.
Of the eggs still in the water, there are oval active larvae metagonimusa - miracidia, able to move, since they are supplied with cilia (cilia); In addition, they have their own germ cells for further asexual reproduction, and for access to the body of snails - a dense shoot-proboscis.
Eggs swallowed by shellfish open in their stomach and intestines, releasing larvae, and already free miracidia by their proboscis pave their way into the liver of snails. But not for nutrition: they exist pre-accumulated glycogen reserve. Their task is to remove the shell and pass to the stage of the passive larva in the form of an elongated cavity. These are maternal sporocysts, in which daughter sporocysts - redia (having muscles, mouth and intestines) begin to develop from the embryonic cells.
In turn, redias are transformed into cercariae - an active larval form. As these larvae leave the mollusks and enter the water, the structure of the metagonimus at this stage allows it to move in search of a second intermediate host, the fish. In the gills and flesh of fish cercariae come to rest and form double-coated cysts - encapsulated in metacercaria. And this stage is contagious for the ultimate host - a person: having got into the intestine, the metacercaria attach to its walls and develop to the stage of an adult parasite, and a new life cycle of the worm begins, which lays new eggs.
Symptoms of the metagonimus
Helminthiasis caused by metagonimus, in parasitology is called metagonism. Often, the invasion proceeds asymptomatically, or such key meta-antimus symptoms as diarrhea and abdominal pain are taken as a common intestinal disorder.
It should be borne in mind that in addition to this, the symptoms of metagonimus are manifested by nausea, general malaise with lethargy and a sense of loss of strength, a deterioration in appetite until its complete loss.
Invasion with this helminth is accompanied by the production of antigens by parasites, which leads to sensitization of the human body and the development of an immune response (the synthesis by mast cells of IgE antibodies) in the form of eosinophilia-an increase in the amount of protective granulocyte leukocytes (eosinophils) in the peripheral blood.
Against this background, lymph nodes can become enlarged and become painful, there is an increase in the liver and spleen (hepatosplenomegaly), overcome headaches and pains in the muscles, swell the face, and the skin becomes covered with urticaria.
In extreme cases - when metagonimus penetrate deep into the mucous membrane - the eggs laid by them can get into the blood or lymph flow and find themselves in the brain and spinal cord or in the heart. Around the egg, granulomas can form, causing seizures, neurological disorders, or heart failure.
In children, a non-identified, latent, chronic metanigonosis can lead to growth retardation and developmental lag.
Therefore, the prognosis of this helminthiosis largely depends on timely diagnosis and treatment, although, according to experts, the duration of the disease does not exceed one year.
Diagnostics of the metagonimus
Metagonimosis is diagnosed on the basis of an analysis of the feces in which the eggs of the metagnonus are found, since adult worms can be seen in the feces only after the drug therapy.
However, accurate diagnosis of the metagnonym only by microscopic identification of eggs in feces is difficult due to the fact that the eggs of most trematodes are similar in size and morphology, and the eggs of Metagonimus yokogawai are indistinguishable from the eggs of such flatworm flukes as H. Heterophyes, Clonorchis sinensis, Opisthorchis felineus or Opisthorchis viverrini.
A common diagnostic procedure is a general blood test for eosinophils. The anomalous content of eosinophils in the blood count is 500 and above eosinophils / μl. At the rates of 1500-5000 eosinophils / μl, mild eosinophilia is diagnosed, and at more than 5000 - severe.
It is also important to find out whether the patient has metemonimus-endemic regions and eaten fish.
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Treatment of the metagonimus
Standard treatment of the metagononus is performed using one of two anthelmintic drugs: Praziquantela or Nichlosamide.
The drug Praziquantel (other trade names - Azinox, Biltricide, Tsezol, Tsistritsid) in tablets of 0.6 g for oral use is taken once a day in a dose of 0.04 g per kilogram of body weight. Tablets are taken whole, with food, washed down with water. The second scheme: 0.02 g per kilogram - twice a day (with an interval of 4-5 hours).
Side effects of Praziquantel are expressed in nausea and vomiting, abdominal pain, headache, skin itch and rash, insignificant body hyperthermia and drowsiness. This remedy is not allowed for pregnant and lactating women.
The drug Nichlosamide (Biomesan, Fenasal, Cestocid, etc.) in tablets of 0.25 g should be taken by adults and children after 12 years of 8-12 tablets for 24 hours: 2 tablets every 4 hours. Children 5-12 years 2 tablets with intervals of 5-6 hours: children 2-5 years - 2 tablets a day (morning and afternoon). The course of treatment is 4 days. At the same time, it is necessary to use salt laxatives, as well as to eat light foods in liquid form. Among the side effects of this drug are skin itching and dyspepsia, among the contraindications there are stomach ulcer, renal and hepatic dysfunction, low hemoglobin level in the blood and gestation period.
Prevention
The simplest prevention of metagonimus infection involves deep heat treatment of raw fish and hygiene (including after processing the fish before cooking it). In countries endemic for the metagonimus, this is difficult to do, because in Southeast Asia, many people eat raw or pickled fish within traditional cuisine.
According to the Korean Journal of Parasitology, the metronimus is the most common intestinal parasite in Korea, Japan, China and Hong Kong - due to the frequent consumption of fish in its raw form.