Clinical Aspects

Clinical Aspects of Schistosomes


Diagnosis

There are several method to identify the infection of the schistosomes. Shown here are the main diagnostic procedures.

1. Detection of Eggs
1-1. Detection from feces Feces of the infected patient contains eggs of schistosomes. If the egg-contained feces are diluted with water, the eggs will hatch and the miracidia will escape to swim about the water. Miracidia prefer light (positive phototaxis), so they can be collected by spotted light. Infection is thus identified by miracidium.
1-2. Detection from the patient's tissue It is difficult to detect eggs from the feces from the chronically infected people. Such people, identification of infection is the detection of eggs from their visceral(e.g. liver, intestine) tissue that are obtained by endoscopic biopsy. Eggs are detected by histopathological examination.
2. Immunological Diagnosis
2-1. CircumOval Precipitation test (COP,abbreviation) Plasma of the infected patient contains the antibody against the egg of schistosome. So if the eggs (it is OK either live- or fixed-) are added to infected patient's plasma, antibody will react against the eggs and will form vacuolar precipitation around them. Recently, it is found that the available antigen is not only the egg but also the miracidia and cercariae. Thus, COP-like precipitation is also seen if the antigen is miracidium or cercaria. In these case, precipitaion phenomena can be detected by immobility of live miracidia (or cercariae). Such tests are called Miracidial(or Cercarian) Immobilization tests.

Treatment

1. Chemotherapy

Until recently, there were no special remedy for schistosome worms. However, there are several insecticide drugs are used to cure schistosomiasis.

Praziquantel (PZQ)
Praziquantel, Praziquantel leads the prognosis of the all types of schistosomiasis very good if the diagnosis is correct and early. Praziquantel is a heterocyclic pyrazine - isoquinolone component, which is special structure compared with other antihelminthics. This drug is also effective to other trematodes. In China, the amount of schistosomiasis patient is dramatically reduced thanks to the domestic praziquantel.
Metrifonate
Metrifonate is administrated for schistosomiasis due to S. haematobium. Main component of this drug is organophosphorus, so it may occur cholinergic symptoms according to its anti - cholinesterase function.
Oxamniquine
Oxamniquine is administrated for schistosomiasis due to S. mansoni.
Detailed protocol of schistomicidal chemotherapy is reported on WHO technical report 830.

2. Treatment for chronic schistosomiasis patients

Chronic patient has hepatosplenic involvement. For these symptoms, the main strategy is to perform the symptomatic treatment. Doctors must watch the systemic conditions of the patient and consider the best way to reduce the uneasiness.

Recently, however, there are reports that the condition of hepatosplenic involvement of chronic schistosomiasis seems to be reversible. It is said that hepatosplenic condition may be improved if the proper schistosomicide therapy is performed.


Prevention and Extermination

There is no infection unless the intermediate molluscan(snail) host is present. Since it is the best way to prevent this disease is to abolish the snail host. Two ways are appropriate to exterminate them: first is to kill snail, and second is to alter the surrounding environment (e.g. surface the shore of river with concrete) to become difficult to live for the snail.

When you enter the endemic area, be aware that you must not bathe in the river or pond with no attention. You must cover your exposed skin to prevent cercariae to penetrate your skin when you have to enter into the water by all means.

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