Alveolar echinococcosis is a parasitic disease caused by the larvae of the tapeworm alveococcus and occurs with the formation of a primary focus in the liver. In the uncomplicated stage, manifestations of alveolar echinococcosis include urticaria, itching, hepatomegaly, heaviness and pain in the right hypochondrium, bitterness in the mouth, belching, nausea. Complications of alveolar echinococcosis may include suppuration of a parasitic tumor, breakthrough of formation into the abdominal or pleural cavities, mechanical jaundice, portal hypertension, metastasis of alveococcus to the brain and lungs. Ultrasound and liver scintigraphy, angiography, radiography/CT of the abdominal cavity and chest are used for diagnosis. Surgical treatment of alveolar echinococcosis is complemented by antiparasitic therapy.
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Alveolar echinococcosis (alveococcosis or multicameral echinococcosis) is a cestodosis, the causative agent of which is the larval stage of the helminth Alveococcus multilocularis, which causes tumor-like liver damage with subsequent infiltrative growth or metastasis to the lungs, brain and other organs. Human alveolar echinococcosis is one of the rare natural focal helminthiasis, the incidence of which in endemic areas is 0.01-0.08%. Cases of alveococcosis occur in Canada, the USA, Europe (Germany, Austria, France, Switzerland), Asia, Russia. The disease is more often infected by young and middle-aged people, mainly engaged in hunting.
For humans, the larval stage of the helminth Alveococcus multilocularis, belonging to the flatworms of the Echinococcine subfamily, is dangerous. Mature forms of alveococcus are similar in structure to echinococcus, but differ in the number of hooks on the scolex (usually 28-32 pcs.), the absence of lateral branches in the uterus, the location of the genital opening in the anterior part of the segment. The main difference between the parasites lies in the structure of the finna, which in alveococcus has the form of cluster-shaped vesicles filled with gelatinous mass. Daughter vesicles are formed by budding and grow outward, not inward, as in Echinococcus.
Adult alveococcus has a size of 1.6-4 mm, consists of a head with 4 suction cups and hooks, 2-3 segments. In the last segment there is a spherical uterus containing about 400 eggs. Ribbon helminth parasitizes in the intestines of arctic foxes, wolves, foxes, dogs, cats, which are the main hosts of alveococcus. Mature eggs with animal feces are released into the environment, from where they enter the body of intermediate hosts (mice, muskrats, river beans, nutria and humans), where the larval development of the parasite takes place. Human infection with alveococcosis can occur when helminth oncospheres are introduced into the mouth during hunting, cutting carcasses of wild animals, removing and processing skins, contact with pets, eating wild berries and herbs contaminated with helminth eggs.
In the human body, the larva of alveococcus leaves the egg and enters the liver with the blood flow, where it almost always lingers. Primary alveolar echinococcosis of other organs is extremely rare. In the liver, the larva transforms into a bubble with a diameter of 2-4 mm, which begins to multiply by exogenous budding. Gradually, a dense, fine-grained parasitic tumor with a diameter of 0.5 to 30 cm or more is formed in the connective tissue stroma of the liver.
In the section, the node of the alveococcus has the appearance of a nostrum cheese (or porous fresh bread), consisting of a large number of chitinous bubbles. Similarly to a malignant tumor, a parasitic node is able to germinate into surrounding tissues and organs (omentum, diaphragm, pancreas, right kidney, adrenal gland, lung, etc.), lymphatic pathways and blood vessels, spreading with the blood flow through the body and forming distant metastases, most often in the brain.
Symptoms of alveolar echinococcosis
In the development of alveolar echinococcosis, asymptomatic, uncomplicated and complicated stages are distinguished. The nature of the course of the disease can be slowly progressive, actively progressive and malignant. The preclinical stage of alveolar echinococcosis can last for many years (5-10 years or more). At this time, patients are worried about urticaria and itching. Detection of alveolar echinococcosis during this period usually occurs with the help of ultrasound performed for another disease.
In the early manifest stage, the symptoms are not very specific, including hepatomegaly, severity and dull pain in the right hypochondrium, pressure in the epigastrium, bitterness in the mouth, nausea. Examination often reveals an increase and asymmetry of the abdomen; palpation of the liver determines a dense node with an uneven bumpy surface. Patients feel weakness, loss of appetite, weight loss. Periodic attacks of hepatic colic, dyspeptic phenomena are also possible.
The most common complication is mechanical jaundice caused by compression of the biliary tract. In the case of bacterial infection, a liver abscess may develop, which is accompanied by increased pain in the right hypochondrium, the appearance of hectic fever, chills, torrential sweats. With a breakthrough of the parasitic cavity, purulent cholangitis, peritonitis, pleural empyema, pericarditis, pleurophepatic and bronchophepatic fistulas, aspiration pneumonia can develop.
In the case of compression by a tumor conglomerate of the liver gate, portal hypertension occurs, accompanied by varicose veins of the esophagus, esophageal and gastric bleeding, splenomegaly, ascites. When the kidneys are interested, proteinuria, hematuria, pyuria develops, urinary tract infection joins. The consequence of immunopathological processes is the formation of chronic glomerulonephritis, amyloidosis and chronic renal failure.
Metastasis of alveococcus most often occurs in the brain; in this case, focal and cerebral symptoms occur (Jackson’s attacks, mono- and hemiparesis, dizziness, headaches, vomiting). Severe and transient course of alveolar echinococcosis is observed in patients with immunodeficiency, pregnant women, and people suffering from severe concomitant diseases. It often ends fatally.
When examining patients with suspected alveolar echinococcosis, an epidemiological history is revealed (living in endemic zones, hunting, gathering wild berries, processing skins and carcasses of wild animals, occupational risks, etc.). Confirm the diagnosis:
- Allergological markers. The early stages are characterized by positive allergic tests (eosinophilia, Kazoni reaction with echinococcal antigen).
- Analyzes. Specific methods of laboratory diagnostics of alveolar echinococcosis include immunological reactions (RIGA, RLA, ELISA), PCR.
- Instrumental methods. To detect liver alveococcosis, the size and location of the parasitic node, abdominal cavity X-ray, ultrasound and liver Dopplerography are used. A non-invasive alternative to arteriography and splenoportography is computed tomography. In difficult situations, liver scintigraphy and diagnostic laparoscopy are used.
If alveolar echinococcosis is suspected, other focal liver lesions are excluded: tumors, hemangiomas, polycystic, cirrhosis, echinococcosis. To detect metastases, chest X-ray, MRI of the brain, ultrasound of the kidney and adrenal glands, etc. are performed.
Treatment of alveolar echinococcosis
Surgical treatment supplemented with antiparasitic therapy is indicated for alveolar echinococcosis of the liver. Most often, the operation of choice is liver resection within healthy tissues (segmentectomy, lobectomy), but radical removal of a parasitic tumor is possible only in 15-25% of cases. If radical excision of the node is impossible, its partial resection or peeling is performed, followed by infiltration with disinfectants or destruction of parasitic tissue by cryotherapy. In some cases, the operation of marsupialization of the parasitic cavity, stenting of the bile ducts is used. Systemic antiparasitic therapy is carried out with imidazothiazole derivatives.
Prognosis and prevention
The slow and asymptomatic development of a parasitic tumor leads to the fact that in most cases it is diagnosed late, which often does not allow radical treatment. The prognosis is quite serious: without treatment, the 10-year survival rate does not exceed 10-20%. The death of patients occurs due to purulent complications, liver failure, profuse bleeding, tumor germination into nearby organs with a violation of their functions, distant metastasis to the brain, etc.
Prevention is reduced to carrying out deworming of domestic animals, veterinary supervision, compliance with precautions when interacting with wild animals, sanitary and educational work with the population of endemic areas. Persons at increased occupational risk of infection (shepherds, hunters, animal farm workers, etc.) are subject to regular screening examination.