Parasitology

Schistosomas
February 2008

Schistosomiasis causal Agents - Cercariae are transformed into schistosomula

- Schistosomiasis is caused by digenetic blood after skin penetration and find entry superficial
trematodes lymphatic vessels or subcutaneous veins to reach
- The three main sp. infecting humans are: the lungs
o S. haematobium - From pulmonary circulation, schistosomulae
o S. japonicum migrates to the portal vein where they mature
o S. mansoni - Egg deposition begins from the 24th- 27th day
- Two other sp, more localized geographically are S. after cercarial penetration
mekongi and S. intercalatum
- In addition, other sp. of schistosomes, which
parasitize, bisrds and mammals, can cause
cercarial dermatitis in humans

Schistosoma japonicum
- Schistosoma japonicum or oriental blood fluke
- Endemic in China, Philippines, Sulkawesi,
Indonesia
- In the Phil. the first report of schistosomiasis was
made by Woolley in 1906
- Strains from different geographic areas are
distinct although all require Onchomelania snails
as intermediate host

Host Range
- Wide range of host
- Dogs, pigs, cats, carabaos, cows, rodent,
monkeys- found to be naturally infected
- Some hosts such as humans, monkey, rabbits and
mice are considered permissive hosts (S.
japonicum matures and oviposists over extended
periods)
- Others are non-permissive hosts

Life Cycle
- Adult male and female worms are primarily Eggs are eliminated with feces or urine . Under optimal
parasites of the portal vein and its branches conditions the eggs hatch and release miracidia , which
- Females: lay – 200 immature eggs in the swim and penetrate specific snail intermediate hosts . The
branches of the portal veins which require 10-12 stages in the snail include 2 generations of sporocysts and
days to mature the production of cercariae . Upon release from the snail,
- Eggs escape through ulcerations into the the infective cercariae swim, penetrate the skin of the human
intestinal lumen → exported to feces host , and shed their forked tail, becoming schistosomulae
- Embryonated egg comes in contact with water . The schistosomulae migrate through several tissues and
hatches → liberates miracidium stages to their residence in the veins ( , ). Adult worms
- Miracidia infect small (intermediate host in humans reside in the mesenteric venules in various
Onchomelania hupensis quadrasi) and develop locations, which at times seem to be specific for each species
into sporocysts . For instance, S. japonicum is more frequently found in the
- Sporocysts develop into cercariae superior mesenteric veins draining the small intestine ,
- Cercariae leave snail host and infect definitive and S. mansoni occurs more often in the superior mesenteric
hosts who come in contact with water by skin veins draining the large intestine . However, both species
penetration can occupy either location, and they are capable of moving
- 60-70 days from miracidial infection of the snail between sites, so it is not possible to state unequivocally that
host to foremation of cercariae one species only occurs in one location. S. haematobium
most often occurs in the venous plexus of bladder , but it

KIB 1 of 5
 Parasitology – Schistosomas by Dra Page 2 of 5

can also be found in the rectal venules. The females (size 7 - acute stages present with fulminating
to 20 mm; males slightly smaller) deposit eggs in the small menigoencephalitis with fever, headache,
venules of the portal and perivesical systems. The eggs are confusion, lethargy and coma
moved progressively toward the lumen of the intestine (S.
- Chronic cases: gives a clinical picture of a
mansoni and S. japonicum) and of the bladder and ureters (S.
haematobium), and are eliminated with feces or urine,
tumor with localizing signs and inc. intracranial
pressure
respectively . Pathology of S. mansoni and S. japonicum
schistosomiasis includes: Katayama fever, hepatic
- Among Filipinos, cerebral schistosomiasis is
perisinusoidal egg granulomas, Symmers’ pipe stem associated with pathology in other organs (liver
periportal fibrosis, portal hypertension, and occasional and intestines)
embolic egg granulomas in brain or spinal cord. Pathology of
S. haematobium schistosomiasis includes: hematuria, Diagnosis
scarring, calcification, squamous cell carcinoma, and Immunodiagnosis
occasional embolic egg granulomas in brain or spinal cord. 1. intradermal test for immediate cutaneous
hypersensitivity using adult worm extracts
2. indirest hemagglutination using adult worm
Pathology and egg antigens
Main pathology: due to host granulomatous reaction to 3. circumoval prepitin test (COPT)
eggs deposited in the liver and other organs 4. ELISA usibg soluble antigens of adults and eggs
- Quantity of cercariae determine severity of
infection - Only COPT, ELISA, and indirect hemagglutination
- cercarial penetration may result in dermatitis using egg antigens should be used because these
- Schistosomular migration causes superficial lung were most specific
petechiae and pneumonitis
- After egg deposition, there is a granulomatous COPT
hypersensitivity reaction around it - demonstrates formation of bleb or septate ppt
- most serious consequences of granuloma attached to one or more points on the egg
formation in liver is obstruction of the surface after incubation of the eggs in a
intrahepatic portal branches portal patients’ serum
hypertension splenomegaly ascites - Currently regarded as the method of choice
for the definitive diagnosis of schistosomiasis
Clinical Aspects in the Phil
Course of infection divided into 3 progressive stages - may take more than 2 years to become neg.
1. Incubation: corresponds to period from
cercarial penetration and schistosomular Adult Schistosomes
migration to maturation
2. period of early egg deposition and extrusion - Adult worms in humans reside in the mesenteric
3. period of tissue proliferation venules in various locations which at times seem
to be specific for each sp.
 Early schistosomiasis - S. japonicum is more frequently found in the
- itching, chills, fever, cough superior mesenteric veins draining the small
intestine
 Colonic schistosomiasis - S. mansonii occurs more often in the superior
- Ulceration caused by eggs result in dysentery mesenteric veins draining the large intestines
or diarrhea o However, both sp can occupy either
- Chronis stage, it is usually asymptomatic buut location, and they are capable of moving
occasional bouts of diarrhea may occur between sites
- Occasionally chronic colonic schistosomiasis is - S. haematobium most often occurs in the venous
associated with malignancies plexus of bladder but it can be found in the rectal
venules
 Hepatosplenic disease - Have separate sexes unlike other trematodes
- hepatosplenomegaly, ascites, collateral - With large sucker capping the anterior end, a
circulation ventral sucker and a gonophore located posterior
to the ventral sucker
 Pulmonary schistosomiasis - Sucker aid in movement; enables flukes to
- Principal manifestation is cor pulmonale from maintain position inside the veins
lung obstruction of lung vasculature due to - Incomplete digestive systems; excretory system
granuloma formation and fibrosis made up of flame cells. These internal structures
are surrounded by circular and longitudinal
 Cerebral schistosomiasis muscles
- worms ingest rbc and pssess a protease that
breaks down globulin and hemoglobin
 Parasitology – Schistosomas by Dra Page 3 of 5

- Utilize glucose and are presumed to absorb technique (20-50 mg of fecal material) or the
nutrients through the body wall Ritchie technique
- Eggs can be found in the urine in infections with
Male Female S. haematobium (recommended time for
- shorter, - 15-26 mm by collection: between noon and 3PM) and with S.
sturdier 0.3 mm japonicum
- Measures: 12- - Single - Detection will be enhanced by centrifugation and
20 mm in pyramidal exam of the sediment
length by 0.4- ovary located in - Quantification is by using filtration through a
0.5 mm the midline Nucleopore membrane of a standard volume of
diameter urine followed by egg counts on the membrane
- Has a - Tissue biopsy (rectal biopsy for all sp and biopsy
gynecophoral of the bladder for S. haematobium) may
canal where the demonstrate eggs when stool or urine exam are
longer female is negative
held
- Testes arranged Antibody Detection
in one row - can be useful in both clinical management (e.g.
above the recent infections) and for epidemiologic surveys
ventral sucker - can be useful to indicate schistosome infection in
patients who have traveled in schistosomiasis
Pathology endemic areas and in whom eggs cannot be
S. mansoni and S. japomicum schistosomiasis: demonstrated in fecal fecal and urine specimens
- Katayama fever, hepatic perisinusoidal egg - Test sensitivity and specificity vary widely among
granulomas, Symmers’ pipe stem periportal the many tests reported for the serologic
fibrosis, portal hypertension, and occasional diagnosis of schistosomiasis and are dependent
embolic egg granulomas in brain or SC on both the type of antigen preparations used
(crude, purified, adult worm, egg, cercarial) and
S. Haematobium schistosomiasis: the test procedure
- hematuria, scarring, calcification, squamous cell - At CDC, a combination test with purified adult
ca, and occasional embolic egg granulomas in worm antigens is used for antibody detection
brain and spinal cord - All serum specimens are initially tested by FAST-
ELISA using S. mansoni adult microsomal antigen
Clinical Features (MAMA)
Continuing infection may cause granulomatous - A positive reaction (> 8 units/µl serum) indicates
reactions and fibrosis in the affected organs, which infection with Schistosoma sp
may result in manifestations that include: - Sensitivity for S. mansoni infection is 99%, S.
- colonic polyposis with bloody diarrhea haematobium 95%, S. japonicum, <50%
(Schistosoma mansoni mostly) - 99% specificity for detecting schistosome
- portal hypertension with hematemesis and infection
splenomegaly (S. mansoni, S. japonicum) - Because test sensitivity with MAMA is reduced for
- cystitis and uretritis (S. haematobium) with sp. other than S. manson, immunoblots of the sp
hematuria which can progress to bladder cancer appropriate to the patiens’ travel history are also
- pulmonary hypertension (S. mansoni, S. tested to ensure detection of S. haematobium and
japoniocum, more rarely S. haematibium S. japonicum infections.
- glomerulonephritis central nervous system lesion - immunoblots with adult worm microsomal
Laboratory Diagnosis antigens are sp-specific; a positive reaction
- Microscopic id of eggs in stool or urine: most indicates the infecting sp
practical method of diagnosis - presence of antibody is indicative only for
- Stool examination for S. mansoni or S. japonicum schistosome infection at some time and cannot be
infection correlated with clinical status, worm burden, egg
- urine exam foe S. haematobium production, or prognosis
- Eggs can be present in the stool in infections with
all Schistosoma sp.
- The examination can be performed on a simple
smear (1-2 mg of fecal materials)
- Enhance detection of eggs by repeated exam
and/or concentration procedures (such as the
formalin- ethyl acetate technique)
- Field surveys and investigations purposes: Diagnostic Findings Microscopy
quantify egg output by using the Kajo-Katz
 Parasitology – Schistosomas by Dra Page 4 of 5

Eggs of S. mansoni bent tip,

These eggs are large resembles S.
- Length: 114-180 µ haematobium
ant end
- Have a characteristic shape with a prominent egg except it
and
lateral spine near the posterior end is longer,
terminal
- The anterior end is tapered and slightly curved thinner and
spine, miracidium
- When the eggs are excreted, they contain a has longer
sometime
mature miracidium (visible especially in the spine, found
s “spindle
first picture) in feces,
shaped”
- Egg of S. japonicum debris mat
- Egg is typically oval/subspherical and has a adhere to
vestigial spine shell
- S. japonicum eggs are smaller (68-100 µ by 45-
80 µ) than those of the other sp
- Eggs of S. haematobium
- In this sp the eggs are large and have a Characteristics of Schistosoma Eggs
prominent terminal spine at the posterior end
- Length 112-170 µ Treatment
- greater magnification shows the miracidium - safe and effective drugs are available
inside the egg - DOC: Praziquantel
Oxamniquone: tx for S. mansoni in which Praziquantel is less
Stage of Special
effective
Species Shape Dev when Features &
passed variations
Geographic Distribution
Lateral spine.
Elongated - S. mansoni is found in parts of S. America and the
Found in
, Caribbean, Africa and the Middle East
feces rarely
prominent - S. haematobium in Africa and the Middle East
in urine. Eggs
lateral
Embryonat discharged at - S. japonicum in the Far East
spine near
ed, irregular - S. mekongi and S. intercalatum are found locally
posterior
S. mansoni contains intervals; in Southeast Asia and central West Africa,
end, ant
mature may not be respectively
end
miracidium found in - In the Phil, there are 24 endemic provinces:
tapered
stool. are rare Sorsogon, Oriental Mindoro, Samar, Leyte, Bohol,
and
in chronic and all provinces in Mindanao island except
slightly
stages of Misamis Oriental
curved
infection - Highest prevalence of infection is in children 5-15
Oval with y/o
small
lateral Summary
spine,
may Found in Organis Transmiss Diagno
appear as Embryonat feces.Often Symptom Tx
m ion sis
S. small ed Contains coated with Dermatitis,
japonicum hook or mature debris and abdominal pain, Praziquantel
“knob” miracidium maybe S. Skin
bloody stool, Eggs
located in overlooked manson penetrati
periportal in
a S.japonic on by
um fibrosis, Stool
depressio cercadia
hepatosplenomeg
n in the aly, ascites, CNS
shell
Praziquantel

Elongated Dermatitis,
Terminal Skin urogenital Eggs
, rounded S.
Embryonat spine. Found haematobi penetrati cystitis, in
S. anterior
ed Contains in urine, occ um on urethritris, and urine
haematobi ens,
mature in feces, egg bladder Ca
um terminal
miracidium ofte covered
spine at
with debris
post end
S. Elongated Embryonat Terminal
intercalatu with ed Contains spine long, woncee.. mjo gnulo ko ng konti ung outline.. pnagsama2 ko ung
m tapered mature slender with sa japonicum.. bka mjo mgulo kung ndi macompare no? Ngaun q
 Parasitology – Schistosomas by Dra Page 5 of 5

lng naisip.. kc knina ampangit tgnan.. aun, kung gs2 nyo nun dti,
kau na mag-aus! Hehehe.. tmadz nq..
- malta