Clinical Aspects of Schistosomes
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.
Until recently, there were no special remedy for schistosome
worms. However, there are several insecticide drugs are used to
Detailed protocol of schistomicidal chemotherapy is reported
on WHO technical
- Praziquantel (PZQ)
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 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 is administrated for schistosomiasis
due to S. mansoni.
2. Treatment for chronic
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.