3. Shistosoma Species
– Introduction
– Importance
– Geographical distribution
– Host range
– Transmission
– Clinical findings
– Diagnosis
– Fecal examination
– Treatment
– Precautions
4. Schistosomiasis/Bilharziosis
– Synonym : snail fever and bilharzia
• A disease caused by parasitic flatworms called
schistosomes.
– It infects the urinary tract or the intestines.
• Symptoms may include:
– Abdominal pain, diarrhea, bloody stool, or blood in
the urine.
– Those who have been infected a long time may
experience :
– liver damage, kidney failure, infertility, or bladder
cancer (squamous cell carcinoma).
– In children, it may cause poor growth and learning
difficulty.
5. Schistosoma mansoni
They are:
Trematodes
– Diecious
– Male is shorter and stouter than the female
– Lateral margins of the male are folded to form
gynaecophoric canal
– Suckers with delicate spines
– Testes : 4-8
– Eggs are non-operculated and
– When laid are fully embryonated
– Embryo: ciliated embryo = miracidium
6. Schistosoma Japonicum
– The S. japonicum worms are:
– yellow or yellow-brown.
– The males of this species are slightly larger than
the other Schistosomes measure ~ 1.2 cm by
0.5 mm.
– The females measure 2 cm by 0.4 mm.
The adult worms are longer and narrower than the
related S. mansoni worms.
7. Terms used in description
– Acetabulum: a muscular organ of attachment also
called as “sucker”.
– Distomata: having 2 suckers.
– Monogenetic: A single generation completing the
life cycle.
– Digenetic: Two generations, a sexual and an
asexual the life cycle.
8. Larval stages
• Miracidium: The first larval stage coming out of the trematode egg
in water. Infective to mollusc only.
• Sporocyst : The second larval stage of trematode occuring in
mollusc .Asexual multiplication occurs in shistosomes in this stage.
• Redia: The third larval stage of the trematode, and Asexual
multiplication occurs in all the trematodes except shistosomes as
there is no stage of redia formation in shistosomes.
• Cercaria: The final stage of larval development in mollusc having a
body and a tail.
• Escapes into surrounding water
• remains free or encysted on vegetables
• Shistosomulum: Immature/growing worm of shistosome in the
definitive host.
10. Geographical distribution:
S.mansoni :
– Various parts of Africa and South America.
Schistosoma japonicum:
– is the only human blood fluke that occurs in China and
Philippines.
Habitat:
– Adult worms in the mesenteric veins of the sigmiodo-rectal area
– Branches of the portal vein in the liver.
Host:
– Definitive host: Man
– Intermediate host: Fresh-water snail
13. Evasion of host immunity:
The worms have many tools that help in this evasion, including the
tegument, antioxidant proteins, and defenses against host
membrane attack complex (MAC).
• Tegument: The tegument coats the worm and acts as a physical
barrier to host antibodies and complement.
• Anti-oxidant proteins:
Host immune defenses are capable of producing superoxide, which
has a tremendous detrimental effect on the worm. However, they
are able to produce a number of antioxidant proteins that block the
effect of superoxide. Schistosomes have four superoxide dismutases,
and levels of these proteins increase as the schistosome develops
and matures.
14. Symptoms and clinical findings:
S.mansoni:
• In patients with intestinal schistosomiasis, the following
symptoms may occur:
– Fatigue
– Abdominal pain
– Diarrhea
– Dysentery
• S.japonicum:
– S. japonicum can lead to:
– liver fibrosis
– liver cirrhosis
– liver portal hypertension
– splenomegaly
15. Diagnosis
• Eggs in stool or urine.
• Detection of antibodies in the blood of the
host/patient
• Rectal bioscopy
• FAT
• Portal veinography
16. Treatment
• In areas where the disease is common, the
medication praziquantel may be given once a
year to the entire group.
• Oxamniquine can also be used for S. mansoni.
• Metrifonate can be used for S.japonicum.
17. Vaccine
• As of September 2014 Eurogentec Biologics
was developing a vaccine against bilharziosis
called Bilhvax in partnership
with INSERM and researchers from
the Pasteur Institute; the vaccine candidate was
starting Phase III trials at that time.
18. Prevention
• Methods to prevent the disease include:
• improving access to clean water
• reducing the number of snails
• Avoidence of swimming , bathing or washing in
the infected area.
• Prevention of polluting the water from human
excreta.
