INTESTINAL (Helminths)
TREMATODA Order: Strigeata

SCHISTOSOMA INTERCALATUM

sm1-ic

Schistosoma spp: life cycle. 
The human schistosomes (blood flukes) are digenic trematodes
of the superfamily Schistosomatoidea.
The adult worms inhabit the mesenteric veins
(S.mansoni, S.japonicum, S.mekongi, S.intercalatum)
or the veins of the vesical and pelvic plexuses (S.haematobium).
The life cycle is common to all species with a sexual generation
in vascular system of the definitive host and an asexual generation
in the intermediate hosts (snails).
1) Embrionated eggs are discharged in faeces and urine;
in water miracidia hatch from the egg and penetrate the intermediate hosts:
different genera of snails (see table)


 

Miracidium

mira1-ic

Schistosoma spp.: miracidium

planorbis1	Biomphalaria	Bulinus-ic	Bulinus	Onchomelania

S.mansoni: intermediate host of S. mansoni are snails
of the genus Biomphalaria (Planorbidae family).
S.haematobium: intermediate host of S.haematobium
are snails of the genus Bulinus
S.japonicum: intermediate host of S.japonicum are snails
of the genus Onchomelania, hupensis spp.

Biomphalaria and Bulinus spp.: Courtesy of Bayer, from Bayer Manual of Pest Control

planorbis1 and Bulinus: Courtesy of Dr. Marc Lontie: Director of the laboratory of the Medisch Centrum voor Huisartsen, Maria Theresiastraat 63a; B-3000 Leuven, Belgium.

 

Schistosome species	Snails
S.mansoni	Biomphalaria spp.
S.haematobium	Bulinus spp.
S.intercalatum	Bulinus spp.
S.japonicum	Oncomelania spp.
S.mekongi	Neotricula spp.

2) after penetration in the snail the miracidium develops into sporocysts and,
in about 4 weeks, thousend of cercariae are produced (asexual multiplication);
3) the infection of the definitive host occurs by penetration of the skin.

Typical transmission site	Contact water 1	Contact water 2	Contact water 3

		Cercaria

sp1-ic                    sp1a-ic                       sp2-ic     

Cercaria sp1: Schistosoma spp.: cercariae are the infective forms.
They measure about 500 micron. After encountering the skin,
the cercariae penetrate and lose the tail transforming into schistosomulae.
sp1a-ic: Cercaria of Schistosoma mansoni from snail.

During the penetration process the cercariae lose their tail
and transform into the larval stage: the schistosomulum

Schistosomulum	Eosinophils and schistosomulum

schisto-ic                  eosi-ic

Schistosomulum
Schistosoma spp.: 1) schistosomulum; 2) antibody dependend cytotoxicity
to schistosomulum
4) after penetration schistosomula migrate to the lungs (in 3-4 days),
and after penetration in the pulmonary capillaries they are carried to
the systemic circulation and to the portal system.
In the hepatic circulation schistosomes mature to adult,
and in pairs they migrate to the mesenteric veins (S.japonicum and mansoni)
and to the vesical plexus (S.haematobium).
After 35 days (S.japonicum, S.mansoni) and 70 days (S.haematobium)
embryonated eggs are excreted in faeces and/or urine.

Control of schistosomiasis is difficult.
The control of snails is critical; environmental sanitation,
safety of supply water and education are essential.

Collecting snails	Molluscisciding spraying	Molluscisciding drip feeding

Schistosoma spp.: snail control with spraying and drip feeding.

si1-ic

Schistosoma intercalatum has been reported from Central and West Africa:
geographic distribution.

sm2a-ic

S.intercalatum: adult schistosomes live in mesenteric venules;
males are shorter and have a ventral infolding from the ventral sucker
to the posterior end forming the gynecophoric canal.
Adult male with female in the copulatory groove.

sm2b-ic

S. intercalatum: Females are slender and longer,
and are held in the gynecophoric canal during copulation.
Adult male with female in the copulatory groove.

si2-ic

Schistosoma intercalatum: S.intercalatum adults live in mesenteric vessels.
Rectal signs and symptoms are the most common findings.
Abdominal pain and bloody diarrhea.
Diagnosis is achieved by faecal examination and rectal biopsies.
Less frequently eggs are recovered in urines and from biopsies 
from urinary bladder or liver.
Eggs are rhomboid in shape and measure 250 µm and have a long terminal spine.
Eggs are acido-alchool resistant and stain red with Ziehl-Neelsen stain.