What is Human Paragonimosis?
Paragonimosis (endemic hemoptysis) is a zooanthroponotic natural focal biohelminthiasis from the trematodoses group with a fecal-oral mechanism of transmission of the pathogen. It is characterized by a primary lesion of the respiratory system with a recurrent course.
Causes of Human Paragonimosis
The causative agent of paragonimosis is the tape flukes Paragonimus westermani. The body is egg-shaped, red-brown in color, 7.5–13 mm long, 4–8 mm wide, 3.5–5 mm thick. The surface of the body is covered with spines. Abdominal sucker around the middle of the body. Eggs are golden brown, oval, with a lid. The sizes of eggs are 63 – 84 x 45 – 54 microns.
People most often found in Paragonimus westermani, living in the Far East, as well as Paragonimus skrjabini (in China), Paragonimus heterotremus (in Southeast Asia), Paragonimus philippinensis (in the Philippines), Paragonimus mexicanus (in Central America and some South American countries ), Paragonimus africanus (in Nigeria and Cameroon) and Paragonimus uterobilateralis (in Nigeria and other West African countries). Paragonimus kellicotti lives on the territory of the USA, however, the loss of people by this helminth is rare.
The ultimate owners of the parasite are pigs, dogs, cats, rats, muskrats, many wild carnivores and humans; Mature helminths in the organism of the final host are localized mainly in the small bronchi, forming fibrious capsules. With urine and feces, paragonim eggs are released into the external environment. When released into the water inside the egg, a larva forms – meratsidy, which is introduced into the intermediate host – freshwater mollusk. After 5 months, after the development and asexual reproduction of larvae, cercariae emerge into the water, penetrating into the body of additional hosts – freshwater crayfish and crabs, where the invasive larva, metacercarium, is formed for the final hosts. In the intestines of the final host, metacercariae are released from the membranes and move to the lungs, sometimes to the brain and other organs, where they reach sexual maturity in the range from 0.5 to 3 months. Metacercariae at 56 ° C die in 20 minutes, at 70 ° C in 5 minutes.
Pathogenesis during Human Paragonimosis
Allocate abdominal and pleuropulmonary paragonimiasis.
Abdominal paragonimosis is caused by the migration of larvae from the intestine into the abdominal cavity. The symptoms of enteritis, hepatitis, and sometimes benign aseptic peritonitis are noted.
The pulmonary paragonimosis is caused by the parasitism of young helminths.
The causative agent’s transmission factors to humans are the thermally uncooked meat of freshwater crayfish and crabs.
The natural susceptibility of people is high.
The pathogenesis is based on inflammation and sclerosis of the lung tissue (sometimes other organs) under the influence of helminths. Clinical manifestations depend on the age of the disease and, possibly, on the intensity of the invasion, although this has not been proven. First, an acute inflammatory reaction develops around adult parasites and their eggs, with eosinophils predominating in the infiltrate. Further around the center the fibrous capsule is formed. Cysts located in the lung parenchyma, erupt into the bronchioles. Their contents are represented by blood, helminth eggs and inflammatory exudate. If the cyst is located subpleurally, pleural empyema may be formed, containing a large number of eosinophils. Over time, in the lesions, the sclerotic processes intensify, and the inflammation subsides. Some foci calcified.
Pulmonary flukes, in addition to the lung parenchyma, often penetrate into other tissues — the pleura, abdominal wall, abdominal organs, brain, causing inflammatory changes and sclerosis. Especially dangerous is brain damage.
It was reported about the frequent development on the background of paragonimosis of severe bacterial infections.
Affection of the abdominal wall and liver is characteristic of the invasion caused by Paragonimus skrjabini.
Symptoms of Human Paragonimosis
The duration of the incubation period of 2 – 3 weeks, with a massive invasion can be reduced to several days.
During the migration of larvae, specific manifestations are absent. Enteritis, hepatitis, benign aseptic peritonitis, allergy symptoms, including myocarditis and pruritus, are possible. Already in the early stage of paragonimosis, symptoms of lung lesions appear in the form of volatile infiltrates, pneumonia, exudative pleurisy.
In acute pleuropulmonary paragonimosis, fever occurs with a temperature of 39 – 40 ° C, chest pain, shortness of breath, cough with purulent sputum, which sometimes contains blood. After 2–3 months, the chronic stage begins with a change of periods of exacerbations and relief, which can last for 2–4 years.
Focal pulmonary fibrosis develops in the chronic phase; radiological detection of foci of darkening with enlightenments in the center. Possible diffuse pneumosclerosis, pulmonary heart, pulmonary hemorrhage, lung cancer. The entry of parasites into the brain leads to encephalitis and meningoencephalitis, a volume process resembling a tumor. With the dissemination of eggs polyserositis is possible.
Affection of the lungs rarely leads to death, however, in the extrapulmonary localization of helminths, the incidence and mortality rates are high. According to one study, extrapulmonary lesions were observed in 30.7% of hospitalized patients with paragonimiasis, and brain damage in 8.4%.
There are acute and chronic brain damage. Acute is characterized by a sudden development of neurological symptoms, usually against the background of a pulmonary pathology. In chronic, frequent epileptic seizures and persistent neurological disorders; radiography of the skull detect calcifications in the form of “soap bubbles”.
When infected with larval forms of paragonimus (P. westermani ichunensis, P. miyazakii, P. huatungensis, etc.), the acute stage of the disease does not differ from the usual pulmonary paragonimosis. In the chronic stage, the disease also proceeds with exacerbations, accompanied by blood eosinophilia and remission. Radiographically detect migrating pneumonic foci, exudative pleurisy on the background of vascular pattern enhancement. Effusion in the pleural cavity can also be right, then left-sided, it is possible polyserosis. In case of a long-term course of the disease, pleural adhesions may develop with limited mobility of the lung and diaphragm.
Complications of the larval paragonimosis are pneumothorax, pulmonary hemorrhage, and sometimes a suppurative process with the formation of a pulmonary abscess or pleural empyema.
Infection with P. szechuanensis occurs with the formation of tight knots in the subcutaneous tissue (sometimes several containing worms and their eggs) of the neck, chest, in the abdomen. The nodes are dense, of different sizes, a little painful on palpation. The skin above the nodes is usually not changed. Invasion is accompanied by subfebrilitet, moderate blood eosinophilia, sometimes coughing, loss of appetite. With the defeat of the subcutaneous tissue of the chest described cases of hydropneumothorax, hydropericardium.
The most severe complication of pulmonary paragonimiasis is hematogenous drift of helminth eggs to the brain, followed by the development of encephalitis, meningoencephalitis, brain damage syndrome (cerebral paragonimosis). Complications of the pulmonary form are pneumothorax, pulmonary hemorrhage, sometimes suppurative process with the formation of lung abscess or empyema. With timely treatment and the absence of complications, the prognosis of larval paragonimiasis is relatively favorable; pulmonary without treatment leads to exhaustion and pulmonary insufficiency, with brain damage, the prognosis is poor.
Diagnosis of Human Paragonimiasis
The diagnosis of pulmonary paragonimosis is established on the basis of the clinical picture, the detection of helminth eggs in sputum, and sometimes in feces. Eggs have a golden brown hue. Their longitudinal size is 80-1000 microns, transverse – 48-60 microns. For light invasion, enrichment methods may be required to detect eggs.
The diagnosis of larval parohonimosis is confirmed by serological reactions with a specific antigen. When P. szechuanensis is infected, the diagnosis is made on the basis of the results of the site biopsy. In the biopsy found the larvae of the parasite.
Treatment of Human Paragonimiasis
Treatment of paragonimosis is carried out with praziquantel (biltricid) at a dose of 60-70 mg / kg body weight per day in three doses after meals with an interval of at least 4 hours for 1-2 days or at a dose of 40 mg / kg according to the same scheme for 4 -5 days.
The prognosis for timely treatment and the absence of complications (pneumothorax, bleeding) is relatively favorable; pulmonary parogonimoz without treatment leads to pulmonary insufficiency, exhaustion. With brain damage, the prognosis is serious.
Prevention of Human Paragonimiasis
Preventing parohonimosis is the proper culinary treatment of the meat of freshwater crayfish, crabs and carnivorous animals, the protection of water bodies from faecal contamination, refusal to drink raw water from natural water bodies. Immunoprophylaxis measures are not developed.