Overview of Schistosomiasis
Pulmonary schistosomiasis is the most common ectopic schistosomiasis caused by the larvae or adult worms of Schistosoma haematobium migrating, developing and parasitizing in the lungs, or the eggs of Schistosoma haematobium depositing in the lung tissues, resulting in the main manifestations of intrapulmonary inflammation, abscess, granuloma, pseudotuberculosis and other lesions. Clinically, in addition to the general symptoms of schistosomiasis, it often manifests respiratory symptoms such as fever, cough, sputum, hemoptysis, chest pain or asthma.
Causes
The feces, urine, sputum and other excretions of schistosomiasis patients contain live eggs, especially in feces as the main source of infection, these excretions containing live eggs can contaminate the water supply, hatch in the water into trichomonads, and the trichomonads form caecal larvae when infected with nail snails. The vector is the snail. The main way of transmission is through the skin and infected water contact, such as swimming, laundry, fishing, etc., can also be in the drinking of raw water from the oral mucosa invasion of the body. People of any sex, age and occupation are susceptible, and the degree of infection increases with age because of repeated infections in endemic areas.
Pathogenesis
Caecal larvae in infected water, when in contact with the human body, invade the skin, take off the tail into the child worms, child worms in the subcutaneous stay 5 ~ 6h, that is, into the small blood vessels and lymphatic vessels, generally in the second day after the invasion of the blood flow through the right heart, the pulmonary artery to reach the pulmonary capillaries, in the invasion of the first 8 ~ 9 days of the child worms to reach the portal system parasitism and development of the adult, and then adult worms retrograde to the hemorrhoidal vein and the inferior mesenteric vein within the parasitism and spawn, from the infection to the spawn generally takes 4 days. The period from infection to egg-laying is generally 4 to 6 weeks. Schistosoma haematobium is mainly parasitic in the blood vessels of the portal system, and the eggs produced by the adult worms are mainly deposited in the submucosa of the intestines and in the liver tissue. If the adult parasites and eggs are deposited in organs and tissues beyond this range and cause damage, it is called ectopic schistosomiasis. Schistosoma eggs may enter the lungs via the hepatic vein or the collateral circulation of the portal vein and are deposited in the lung tissue. Occasionally, schistosomes are ectoparasitized in the lungs, and even females and males combine to lay eggs. Child worms that reach the lungs can cross the alveolar wall capillaries and enter the thoracic cavity, mediastinum, diaphragm and reach the abdominal cavity and enter the portal system. When the acute phase is over or due to repeated infection and long-term infestation of the lungs with small amounts of caecal larvae, pulmonary chronic schistosomiasis is formed.
The migration of the child worms to the lungs can cause pathological changes of allergic pneumonia such as congestion, hemorrhage and eosinophilic infiltration of lung tissues, which often appear 1 to 2 weeks after infection and disappear quickly. The reaction caused by the eggs deposited in the lungs varies according to the degree of maturity: mature eggs can cause tissue necrosis and acute exudative inflammation, and there are often endovascular inflammation and eosinophilic granulomas at the place where the eggs are deposited, and acute abscesses can be formed in case of serious infection; with the death of the eggs, the abscesses will be absorbed to form granulomas, which contain a large number of epithelioid cells and are mixed with foreign giant cells, which is very similar to the tuberculosis nodule, and it is called The granuloma contains a large number of epithelioid cells and foreign body giant cells, which is very similar to tuberculosis nodules, and is called “pseudotuberculosis”. Small granulomas can be gradually fibrotic, and the eggs can occasionally be calcified after death; the immature eggs cause a milder tissue reaction, and although there is also the formation of “pseudotuberculosis”, there are not many eosinophilic granulocytes and neutrophilic infiltration. Pulmonary chronic schistosomiasis is mainly due to the mechanical or chemical stimulation of schistosome eggs deposited in the lungs, causing pulmonary interstitium, bronchial submucosa congestion, edema, ulcer formation, bronchial tubes, bronchioles, narrowing of the lumen of the bronchial tubes, mucosal epithelium and fibroblasts hyperplasia, cellular infiltration and other changes.
Symptoms
The season of onset is mostly in summer and fall, and varies with the amount of invading pathogens and the extent of lung lesions. One to two weeks after acute infection, there are varying degrees of symptoms. Such as flaccid or low-grade fever (a few have high fever), coughing, coughing up sputum, blood in sputum, chest pain or asthma, but also abdominal pain, itching, urticaria and other allergic symptoms. In vivo, the period of mass spawning of adult worms corresponds to 1 month after the initial infection, with a minimum of more than 10 days and a maximum of 2 months, and most of them have an acute onset of illness with varying degrees of severity. Clinical manifestations mainly include fever, intermittent fever, flaccid fever is common, with large fluctuations in the morning and evening, in addition, patients may have a dry cough, shortness of breath, chest pain, palpitations. Dry and wet rales can be heard on lung auscultation. Severe cases can cause diffuse, occlusive pulmonary arteritis, and a few can cause pulmonary hypertension and heart failure. This stage can also cause severe allergic reactions with urticaria, bronchial asthma, angioneurotic edema, and enlarged lymph nodes. Acute abscess formation around the egg can be characterized by shortness of breath, asthma, chest pain, and coughing up bloody or purulent sputum. Accompanying abdominal symptoms such as nausea, vomiting, abdominal pain, and diarrhea are quite common in the early stages and can be part of an allergic reaction, but persistent diarrhea is all due to irritation of the intestinal mucosa by the eggs. The chronic phase of pulmonary schistosomiasis may be characterized by schistosomal chronic bronchitis, recurrent allergic pneumonitis, bronchiectasis, and pleurisy.
Examination
1. Laboratory examination
Acute total white blood cell count and eosinophil count increases, eosinophils generally account for 15% to 20%, occasionally up to 70%, the degree of increase in eosinophils is disproportionate to the severity of the infection, severe patients may not be increased, or on the contrary, see a decrease in the number of neutrophils, or to replace the increase in the number of neutrophils, the condition of the sign of danger. The positive rate of direct smear in fecal examination is not high, so precipitation and incubation methods are usually used. Sputum examination can also find eggs or trichomonads by direct smear or precipitation and incubation. Eggs can be found by rectal mucosal biopsy or pressure film. Immunological tests such as intradermal test for schistosome antigens, cyclic egg precipitation test, membrane test for caecilians, and immunoelectrophoresis to detect antigens can provide an aid to diagnosis.
2. X-ray examination
Most of the patients have clear lung substance changes, which can be seen as increased lung texture, flaky shadows, corn-like changes, and enlarged hilar shadows, etc. In the early stage, both lung textures are enhanced. In the early stage, the texture of both lungs is enhanced, followed by scattered punctate infiltration in both lungs with blurred edges, mostly in the middle and lower lung fields. With the development of the disease, the lung shadows tend to be dense and have a tendency to merge with each other, resembling bronchopneumonia. When the eggs die, the surrounding tissue reaction disappears, the lesion gradually absorbs and shrinks, the edge becomes clear and neat, leaving point-like shadows, which is similar to the performance of cornual tuberculosis, and then the point-like shadows gradually decrease, and sometimes calcification can be seen. Typical X-ray lesions usually disappear gradually within 3-6 months. In a few cases, extensive occlusion of small pulmonary arteries may cause pulmonary hypertension and right heart hypertrophy. If there is a history of repeated infections due to multiple exposure to infected water, there may be old and new, unequal density and uneven size of corn-like shadows in the lung fields. Chronic pulmonary schistosomiasis may show flaky shadows of increased density, with clear boundaries with healthy lung tissue, shaped like inflammatory pseudotumor or tumor.
3. Bronchoscopy
In the acute stage of pulmonary schistosomiasis, in some cases, bronchial mucosal congestion, edema and submucosal yellow particles can be seen under fiberoptic bronchoscopy; in the chronic stage, there are superficial ulcers, corn-like nodules, scarring, narrowing of the lumen of the bronchial tubes, secretion retention and so on. Schistosoma eggs can be found by bronchial brushing and bronchial mucosal tissue biopsy. Eggs are most commonly found in calcified or empty shells (black), and occasionally in mature or immature live eggs, which are colorless and transparent, with the trichinae clearly visible.
Diagnosis
The diagnosis of schistosomiasis is based on a history of living in a schistosome-endemic area and contact with infected water, as well as other symptoms of schistosomiasis in general. x-ray chest radiographs suggest nodular or cornified lesions or inflammatory lesions in the lungs, accompanied by varying degrees of coughing, chest pain, coughing up of blood in the sputum, asthma, and respiratory distress. Schistosoma eggs are found in sputum, or bronchial brushings or bronchial mucosal biopsies; schistosoma eggs are found in feces or in rectal or sigmoid mucosal biopsies. Elevated blood eosinophils and immunologic tests such as positive skin test and positive ring egg test can help diagnosis.
Treatment
The treatment of pulmonary schistosomiasis is the same as that of general schistosomiasis, and the drugs used for the treatment of schistosomiasis include praziquantel, nitrofurans, metronidazole, antimony, hexachloro-p-xylene, nitrothiocyanamide, and so on, with praziquantel being preferred, and praziquantel has the advantages of high therapeutic efficacy, short course of treatment, and fewer adverse reactions, and it can be taken for 1 course of treatment after an interval of 2-3 days if necessary, and 30%-40% of them recur after the treatment, and thus it is necessary to pay attention to the rechecking and Therefore, attention should be paid to review and retreatment.