Paragonimiasis: causes, symptoms, diagnosis, treatment

Paragonimiasis is a biohelminthiasis, which manifests itself mainly by damage to the respiratory organs. Paragonimiasis is characterized by a long-term relapsing course.

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Epidemiology of paragonimiasis

The source of invasion is pigs, dogs, cats, wild carnivores and humans infected with paragonimus. The routes of transmission are food and water. The factors of transmission are thermally unprocessed meat of crabs and crayfish.

At the optimum temperature (27 °C), the development of eggs in water ends after 3 weeks. However, miracidia can emerge from them after several months, which is facilitated by fluctuations in water temperature. The intermediate hosts are freshwater gastropods Melania libertina, M. externa, M. amurensis (Far East), Ampullara luteosota (South America) and others, in which the stages of sporocysts, rediae and cercariae develop successively. Cercariae actively penetrate into additional hosts through areas with a thin chitinous cover - freshwater crabs of the genera Potamon, Eriocheir, Parathelphusa, crayfish of the genera Cambaroides, Procambarus and others.

In crustaceans, cercariae encyst in muscles and internal organs, where they transform into metacercariae, which become invasive after 1.5 months. The body of one crustacean can contain several hundred metacercariae. The final hosts are pigs, dogs, cats, wild carnivores, rodents (rats, muskrats) and humans, who become infected by eating raw or semi-raw crabs and crayfish. Infection can also occur through water, since when infected crustaceans die, metacercariae remain viable in water for up to 25 days. In the duodenum of the final hosts, the larvae are released from the membranes, penetrate the intestinal wall into the abdominal cavity, pierce the diaphragm, both layers of the pleura and penetrate the lungs. Here, fibrous cysts the size of a hazelnut form around the parasite, localized near the roots of the lungs and along the periphery of the lung tissue. A person usually has one parasite in a cyst, rarely two. The parasites reach sexual maturity and begin laying eggs 5-6 weeks after infection. The lifespan of parasites in the lungs exceeds 5 years.

Paragonimiasis is widespread mainly in the countries of Southeast Asia (China, Taiwan, the Indochina Peninsula, Indonesia, the Philippines), as well as in South America (Peru, Ecuador, Colombia, Venezuela). In Russia, in addition to imported cases, limited foci of paragonimiasis are known in Primorsky Krai and the Amur Region. In this region, infection is facilitated by eating a local dish - "drunken crabs", which is prepared from live crabs or crayfish sprinkled with salt and doused with red wine.

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What causes paragonimiasis?

Paragonimiasis is caused by the lung fluke Paragonimus westermanii and some other species of the Paragonimidae family.

P. westermanii is a thick, broadly oval trematode, reddish-brown in color, shaped like a coffee bean. The body size of the lung fluke is 7.5-12 x 4-6 mm with a thickness of 3.5-5 mm. The cuticle is covered with spines; the oral and ventral suckers are almost the same size. The intestinal branches are convoluted and extend to the end of the body. Two lobed testes are located in the posterior third of the body. The lobed ovary and loops of the small uterus are located next to each other in front of the testes. The genital openings are located at the posterior edge of the ventral sucker. Strongly developed vitelline glands are distributed throughout the body from the level of the pharynx to the posterior end of the fluke's body.

The eggs are oval, golden-brown in color, 61-81 x 48-54 microns in size, with a thick shell, a cap, and a small thickening at the opposite end. The eggs are released immature.

Pathogenesis of paragonimiasis

In the pathogenesis of paragonimiasis, the leading role is played by toxic-allergic reactions and the mechanical impact of helminths and their eggs on tissues. During the migration of parasite larvae into the lungs through the diaphragm and other organs (liver, pancreas, kidneys), hemorrhages and sometimes necrosis are observed in them. In the lungs (especially in the lower lobes), in addition to hemorrhages, eosinophilic infiltrates and exudate accumulations are formed. Later, fibrous cysts from 0.1 to 10 cm in size are formed around the parasites. They are filled with a gray-white, chocolate or dark red mass, contain mucus, eosinophils and other leukocytes, Charcot-Leyden crystals, as well as one or more parasites. Cysts often communicate with bronchial branches. After the death of the parasite or its exit from the cyst, its cavity scars over. When the cyst wall is damaged, parasites or their eggs are sometimes carried to the brain, mesenteric lymph nodes, prostate gland, liver, skin and other organs and tissues.

Symptoms of paragonimiasis

The incubation period of paragonimiasis lasts 2-3 weeks, and in case of massive invasion it can be reduced to several days.

In the acute period of the disease, the first symptoms of paragonimiasis develop due to severe enteritis, hepatitis and benign aseptic peritonitis, accompanied by signs of "acute abdomen". Then fever, chest pain, shortness of breath, cough with purulent sputum, sometimes with an admixture of blood, occur. Physical and radiographic examinations reveal exudative infiltrates, and sometimes signs of exudative pleurisy.

After 2-3 months, the disease becomes chronic, characterized by periods of remission and exacerbation, during which typical symptoms of paragonimiasis occur: the temperature rises to 38-40 °C, chest pains and headaches intensify, shortness of breath appears, and coughing produces rusty sputum containing helminth eggs. Hemoptysis is often observed. X-ray examination of the lungs reveals weakly defined rounded shadows with a diameter of 5 to 40 mm with radial linear darkening extending from them. As fibrous cysts form, light vacuoles with clear and smooth outlines 2-4 mm in size are visible inside the shadows.

After 2-4 years, the clinical symptoms of paragonimiasis gradually disappear. After the symptoms of the disease disappear, X-ray examination reveals small isolated foci of fibrosis and single or multiple foci of calcification with a diameter of 2-5 mm in the lungs.

With intensive invasion and long-term course of the disease, pneumosclerosis and “pulmonary heart” syndrome may develop.

When paragonimuses enter the central nervous system, they cause meningitis symptoms and increase intracranial pressure. Optic nerve atrophy, paresis, paralysis, sensitivity disorders, and epilepsy may develop. X-rays of the brain in such patients reveal calcified rounded formations containing dead helminths.

Complications of paragonimiasis

Timely treatment of uncomplicated cases of paragonimiasis gives a favorable prognosis for the disease. In the case of brain paragonimiasis with multiple cysts, the prognosis is extremely unfavorable.

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Diagnosis of paragonimiasis

Differential diagnostics of paragonimiasis is carried out with pneumonia, tuberculosis and pulmonary echinococcosis, as well as tumors. In case of paragonimiasis of the brain, the disease is differentiated from a brain tumor and meningoencephalitis. The parasitic nature of the disease is indicated by a combination of neurological symptoms with characteristic changes in the lungs and the presence of eggs in the sputum.

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Laboratory diagnostics of paragonimiasis

The diagnosis of "paragonimiasis" is established based on the epidemiological anamnesis, clinical data and the results of radiation examination methods (X-ray, CT, MRI), as well as upon detection of parasite eggs in sputum or feces, where they get when swallowing sputum. In the early period, when eggs are not yet excreted by young parasites, ELISA can be used for diagnosis. An intradermal allergy test with antigens from paragonimiasis can also be used.

Treatment of paragonimiasis

Specific treatment of paragonimiasis should be carried out after the relief of allergic manifestations. The drug of choice is praziquantel (azinox), which is prescribed to adults in a daily dose of 75 mg/kg in 3 doses for one to two days. In case of damage to the central nervous system, specific therapy should be carried out only in a hospital due to the possible development of cerebral edema and increased intracranial pressure. Patients are prescribed diuretics and anticonvulsants. Single cysts are removed surgically.

Triclabendazole is also effective and is prescribed in the same dosages as for fascioliasis.

In order to monitor the effectiveness of specific treatment for paragonimiasis, 2-3 months after the end of therapy, a three-time (with an interval of 7 days) control study of sputum is carried out.

How to prevent paragonimiasis?

In areas of paragonimiasis, crustaceans can be eaten only after cooking, ensuring the death of the paragonimiasis. Since water may contain particles of dead crabs and crayfish infested with metacercariae, when swimming in open freshwater bodies, one should be careful not to accidentally swallow water. Paragonimiasis can be prevented by drinking only boiled or filtered water. It is necessary to ensure that water bodies are protected from faecal contamination.