Paragonimiasis is a zooanthroponotic disease from the group of biohelminthiasis caused by a pulmonary fluke, usually parasitizing in the lungs, less often in the brain and other organs. Disease can be manifested by abdominal syndrome, itching of the skin, bronchopneumonia, hemoptysis, pulmonary bleeding, symptoms of meningitis, convulsive seizures, decreased visual acuity. The diagnosis is established on the basis of the clinical picture, the results of sputum microscopy, coprooscopy, radiography, CT and MRI of the lungs and skull, biopsy, laparoscopy. Treatment is carried out with anthelmintic agents; if ineffective, surgical removal of cysts, lung resection is indicated.
Paragonimiasis is a chronic parasitic invasion that develops when infected with trematodes of the genus Paragonimus and proceeds with a predominant lesion of the lungs. Disease is a natural focal disease covering the countries of Southeast Asia (China, Japan, Korea, Indonesia, the Philippines, the Indochina Peninsula), Central and South America (Peru, Ecuador, Venezuela, Colombia), West Africa. The formation of foci of paragonimiasis is facilitated by the traditional consumption of thermally unprocessed meat of freshwater crustaceans by the population. Outside of these regions, the incidence of paragonimiasis is sporadic.
Paragonimiasis is caused by pulmonary flukes, including several closely related species of trematodes of the genus Paragonimus. The most common pathogen is P. westermani, which is a flat helminth of a red-brown shade, shaped like an orange seed. The body of a helminth 7-12 mm long has a cuticle covered with spikes, as well as oral and abdominal suckers. The parasite is a hermaphrodite, after cross-fertilization lays immature eggs up to 0.12 mm long.
A complex cycle of trematode development takes place with a change of hosts: the main ones are humans and animals (pigs, dogs, cats, muskrats, otters, rats), the first intermediate ones are freshwater mollusks; additional ones are freshwater crabs, crayfish and shrimp. Paragonimiasis has a fecal-oral transmission mechanism. Fluke eggs are released from the body of the main host into the environment with feces, less often with sputum and ripen in water. Hatched larvae (miracidia) are actively introduced into the tissues of mollusks and successively pass through the stages of sporocysts, redia and cercaria. Cercariae are able to actively or passively penetrate into the bodies of crabs and crayfish, encyst in muscles and internal organs, developing there to invasive metacercariae.
There is a high natural susceptibility of people to paragonimiasis. The invasion occurs when eating raw meat of infected crustaceans (food route) or when drinking contaminated water (waterway). In the small intestine, the larvae are released from the shells, perforate the intestinal wall and carry out a complex migration to the lungs through the abdominal cavity, diaphragm, pleural leaves. In the pulmonary parenchyma, they form fibrous cysts up to 10 cm in size around themselves, localized along the periphery and at the roots of the lungs. Each paragonimous cyst is filled with inflammatory exudate with an admixture of blood and mucus, usually contains a couple of parasites and their eggs, it is reported with bronchiole. Puberty of the pulmonary fluke occurs 5-6 weeks after infection, egg laying occurs in 65-90 days, life expectancy reaches 5 or more years.
Flukes, their eggs and larvae have a mechanical effect on host tissues, provoke the development of inflammatory and toxic-allergic reactions. The migration of larvae through the abdominal organs and diaphragm causes hemorrhages and necrosis in them. The opening of paragonimous cysts is accompanied by hematogenic dissemination of trematodes and their eggs into the central nervous system, mesenteric lymph nodes, liver, prostate gland, skin and other organs. Eggs, along with sputum, are coughed up or swallowed, getting into the gastrointestinal tract. The cyst cavity after the exit or death of the helminth is scarred, sclerotic processes gradually develop in the lesions, calcification is observed.
The incubation period of paragonimiasis is from several days to 2-3 weeks, clinical manifestations depend on the stage of the disease. During the migration of metacercariae from the intestine to the abdominal cavity, abdominal syndrome is noted with the phenomena of enteritis, acute hepatitis, benign aseptic peritonitis, symptoms of acute abdomen. Skin itching may occur. The introduction of fluke larvae into the lung tissue is manifested by the development of acute bronchitis, bronchopneumonia, hemorrhagic pleurisy.
Acute pulmonary paragonimiasis is characterized by fever (39-40C), shortness of breath, chest pain, cough with sputum with an admixture of blood (hemoptysis), in half of cases – pulmonary bleeding. Patients have fatigue, irritability, tachycardia. With acute brain damage, symptoms of meningitis, meningoencephalitis are observed: increased intracranial pressure, dizziness, severe headache, convulsive seizures with loss of consciousness, narrowing of fields and decreased visual acuity. In the subcutaneous fatty tissue of the neck, chest and abdomen, dense, slightly painful nodes containing helminths and eggs may appear. With extrapulmonary localization of paragonimiasis, the frequency of complications and mortality are high.
After 2-3 months, paragonimiasis turns into a chronic course with a change of periods of exacerbation and subsiding of symptoms. The chronic stage lasts up to 2-4 years and is accompanied by a gradual extinction of symptoms, the appearance of isolated foci of fibrosis and calcification in the lungs, the development of pneumosclerosis, “pulmonary heart” syndrome.
Complications of pulmonary paragonimiasis are pneumothorax, pulmonary bleeding, pleural mooring with limited mobility of the lung and diaphragm, in case of bacterial infection – the formation of an abscess or empyema of the lung. The consequence of severe brain damage can be epilepsy, optic nerve atrophy, paresis, paralysis.
In the diagnosis of paragonimiasis, data from epidemiological anamnesis, clinical picture, laboratory (blood test, sputum microscopy, coprooscopy) and instrumental studies (radiography, CT and MRI of the lungs, CT of the skull, cyst biopsy, laparoscopy), results of allergy tests with antigens of pangonymus are used. In the acute stage, paragonimiasis is rarely diagnosed, a characteristic feature may be a combination of changes in the lungs with neurological symptoms.
The diagnosis of paragonimiasis is confirmed by the detection of oval golden-brown eggs of the parasite in the sputum and feces of the patient. In the first 2-3 months after infection, serological methods (ELISA) that detect specific antibodies to helminth antigens are more informative. In the blood of paragonimiasis, eosinophilia, lymphocytosis, hypochromic anemia are determined. On the radiograph of the lungs, paragonimous cysts are presented in the form of blurred ring-shaped obscurations with smooth smooth borders in one or more pulmonary segments. X-rays of the skull show calcifications in the form of “soap bubbles”. During laparoscopy, hemorrhagic, fibrinous or fibrinous-purulent effusion is detected in the abdominal cavity, in which immature helminths can be detected. Differential diagnosis is carried out in relation to tuberculosis, pneumonia, echinococcosis and lung neoplasms, with brain damage – brain tumors, meningitis.
Treatment and prognosis
In the early stage of paragonimiasis, desensitizing therapy with antihistamines is carried out, with severe organ lesions – a short course of corticosteroids. Specific treatment of paragonimiasis includes taking anthelmintic agents (praziquantel, bithionol), taken after the acute allergic reactions subside. If the central nervous system is affected, the treatment of paragonimiasis is carried out only in a hospital. Anticonvulsants, diuretics are used. In chronic paragonimiasis, general restorative and cardiovascular agents are indicated. In case of ineffectiveness of conservative tactics, lung resection, removal of lung and brain cysts is performed.
With timely treatment of uncomplicated cases of pulmonary paragonimiasis, recovery occurs; with a widespread lesion, the development of pneumosclerosis, the prognosis is serious; with multiple brain cysts, it is extremely unfavorable. Prevention in foci is reduced to the exclusion of raw crustacean meat from food, boiling of drinking water, protection of reservoirs from fecal contamination.