Schistosomiasis
From Medical-Wiki
Schistosomiasis, also called bilharziasis, is an infestation with one of several species of parasitic trematodes of the genus Schistosoma. This parasitic infection is a major source of morbidity and mortality for developing countries in Africa, South America, the Caribbean, the Middle East, and Asia.
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Schistosome life cycle
Schistosomes spend part of their life cycle in a particular species of susceptible freshwater snails. They are released in the form of cercariae, fork-tailed free-swimming larvae approximately 1 mm in length. Cercariae attach to human hosts, migrate through intact skin to dermal veins, and to the pulmonary vasculature. During this migration, they shed their tails and outer glycocalyces. They concomitantly develop double-lipid-bilayer teguments — highly resistant to host immune responses. [1]
The worms then migrate through the pulmonary capillaries to the systemic circulation, which carries them to the portal veins where they mature. Within the portal vasculature, male and female adults pair off. The thin female enters the gynecophoric canal of the stockier 8-mm male worm. Together they migrate along the endothelium to the mesenteric or vesicular veins where they begin to produce eggs. The eggs are highly antigenic and can induce an intense granulomatous response. They migrate through the bowel or bladder wall to be shed via feces or urine. Eggs not shed may remain in the tissues or be swept back to the portal circulation or to the pulmonary circulation. [2]
Clinical presentation of schistosomiasis
Symptomatology
Edema, malaise/general fatigue, pruritus, fevers, nausea, vomiting, lymphadenopathy, diarrhea/dysentery, abdominal pain, urticaria, gastrointestinal bleeding, seizures, myelopathy, cough with or without hemoptysis, palpitations, dyspnea, weight loss, urinary frequency, dysuria, hematuria, and suprapubic/perineal pain may all accompany schistosomiasis. Roughly 10% of patients, usually those with high concentrations of parasites, have symptoms. [3]
Katayama fever
Katayama fever is acute schistosomiasis. It develops after several weeks following a new schistosomal infection, and is a serum sickness. It is accompanied by significant peripheral eosinophilia and circulating immune complexes. The syndrome may be fatal although it typically resolves over a several weeks. Treatment with cidal drugs may worsen the disease and require concomitant use of glucocorticoids.
Initial exposure to species that rely on other primary hosts may cause a swimmers itch. Otherwise, marked dermatological reactions during the initial attachment phase is rare.
Chronic schistosomoiasis
Chronic is far more common than the acute disease. This phase is a result of responses to the eggs. The responses are an immune response with granuloma formation, and associated fibrotic changes.
Those eggs that are retained in the bowel wall cause bloody diarrhea, cramping, and, eventually, inflammatory colonic polyposis. Patients with these symptoms also have an increased rate of recurrent Salmonella. These infections are characterized by positive blood cultures but negative stool cultures.
When eggs are swept back to the portal circulation, they lodge and induce granulomatous reactions in the portal tracts. Hepatocellular function is spared, but the resultant periportal fibrosis leads to portal hypertension and all of its sequelae. Worldwide, schistosomiasis is one of the most common causes of portal hypertension.
Eggs retained in the bladder can lead to hematuria, dysuria, bladder polyps and ulcers. They are associated with an increased incidence of bladder cancer.
If eggs reach the pulmonary circulation, they can cause pulmonary granulomatosis and fibrosis. This leads to pulmonary hypertension and frank cor pulmonale with a high mortality rate.
Ectopic deposition of eggs is accompanied by a wide variety of syndromes of the skin, lung, brain, muscle, adrenal glands, and eyes. Central nervous system involvement can result in transverse myelitis. [4]
Diagnosis of schistosomiasis
Diagnosis of schistosomiasis may utilize identification of eggs or serological tests. Eggs can be recovered from urine or stools. Serological testing is generally accurate, but in longstanding chronic disease may have a relatively high rate of false negatives.
Since schistosomiasis has the capacity to affect all organ systems, lab evaluation and imaging studies may be necessary to evaluate other parts of a differential diagnosis depending upon a patient’s symptoms. [5]
Treatment for schistosomiasis
As noted by the WHO, until the advent of the newer treatments, there was a time when the cure of schistosomiasis was as dangerous as the infection itself. However, the advent of Praziquantel, effective in the treatment of all forms of schistosomiasis and with few side effects, Oxamniquine, used exclusively to treat intestinal schistosomiasis in Africa and South America, and Metrifonate, used for the treatment of urinary schistosomiasis, has revolutionized treatment. [6]
Schistosomiasis bilharziasis, parasitic trematodes, human schistosomiasis, Schistosoma haematobium, S haematobium, Schistosoma mansoni, S mansoni, Schistosoma japonicum, S japonicum, Schistosoma mekongi, S mekongi, Schistosoma intercalatum, S intercalatum, schistosomes
