Download Schistosoma mansoni

Schistosomiasis
Dr. Mohammad Shakeeb, MD
Specialist in clinical
pathology/Microbiology and
immunology
• Schistosomiasis is a major parasitic infection of
tropical areas, with some 200 million infections
worldwide.
• blood flukes: dorsoventrally flattened helminths
• The three schistosomes most frequently
associated with human disease are :
 Schistosoma mansoni.
 Schistosoma japonicum.
 Schistosoma haematobium.
• They collectively produce the disease called
schistosomiasis, also known as bilharziasis or
snail fever.
• The schistosomes differ from other flukes:
They are male and female rather than
hermaphroditic.
Their eggs do not have an operculum.
They also are obligate intravascular parasites
and are not found in cavities, ducts, and other
tissues.
The infective forms are skin-penetrating
cercariae liberated from snails.
These differ from other flukes in that they are
not eaten on vegetation, in fish, or in
crustaceans.
life cycle
• Infection is initiated by ciliated, free
swimming,
freshwater
cercariae
that
penetrate intact skin.
• Enter the circulation
• Develop in the intrahepatic portal circulation
(S. mansoni and S. japonicum)
• In the vesical, prostatic, rectal, and uterine
plexuses and veins (S. haematobium).
• The female has a long, cylindric body, whereas
the shorter male, which appears cylindric, is
actually flat.
• The cylindric appearance derives from folding the
sides of the body to produce a groove, the
gynecophoral canal, in which the female resides
for fertilization.
• Both sexes have oral and ventral suckers and an
incomplete digestive system, which is typical of a
fluke.
• As the worms develop in the portal circulation,
they elaborate a remarkable defense against host
resistance.
• They coat themselves with substances that the
host recognizes as itself; consequently, there is
little host response directed against their
presence in blood vessels.
• This protective mechanism accounts for chronic
infections that may last 20 to 30 years or longer.
• After developing in the portal vein, the male and
female adult worms pair up and migrate to their
final locations, where fertilization and egg
production begin.
• S. mansoni and S. japonicum are found in
mesenteric veins and produce intestinal
schistosomiasis.
• S. haematobium occurs in veins around the
urinary
bladder
and
causes
vesicular
schistosomiasis.
• On reaching the submucosal venules of their
respective locations, the worms initiate
oviposition, which may continue at the rate of
300 to 3000 eggs daily for 4 to 35 years.
• The eggs elicit an intense inflammatory
reaction,
with
mononuclear
and
polymorphonuclear cellular infiltrates and the
formation of microabscesses.
• In addition, the larvae inside the eggs produce
enzymes that aid in tissue destruction and
allow the eggs to pass through the mucosa
and into the lumen of the bowel and bladder
• They are passed to the external environment
in the feces and urine, respectively.
• The eggs hatch quickly on reaching fresh
water to release motile miracidia.
• The miracidia then invade the appropriate
snail host.
• Where they develop into thousands of
infectious cercariae.
• The free-swimming cercariae are released into
the water, where they are immediately
infectious for humans and other mammals.
Pthogenesis
• The infection is similar in all three species of
human schistosomes in that disease results
primarily from the host’s immune response to the
eggs.
• The very earliest signs and symptoms are due to
the penetration of the cercariae through the skin.
• Immediate and delayed hypersensitivity to
parasite antigens result in an intensely pruritic
papular skin rash.
• The onset of oviposition results in a symptom
complex known as Katayama syndrome.
• marked by fever, chills, cough, urticaria,
arthralgias, lymphadenopathy, splenomegaly,
and abdominal pain.
• This syndrome is typically seen 1 to 2 months
after primary exposure and may persist for 3
months or more.
• It is thought to result from the massive release of
parasite antigens, with subsequent immune
complex formation.
• Associated laboratory abnormalities include
leukocytosis, eosinophilia, and polyclonal
gammopathy.
• The more chronic and significant phase of
schistosomiasis is due to the presence of eggs in
various tissues and the resulting formation of
granulomas and fibrosis.
• The retained eggs induce extensive
inflammation and scarring.
• The clinical significance of which is directly
related to the location and number of eggs.
Schistosoma mansoni
• Schistosoma mansoni occurs in Africa,
especially in the tropical areas and the Nile
delta, southern Africa, and Madagascar, Brazil,
Venezuela, Surinam, and certain Caribbean
islands, including Puerto Rico.
• Adult S. mansoni live primarily in the portal
vein and in the distribution of the inferior
mesenteric vein.
• Initial deposition of eggs in the large intestine
may produce abdominal pain and dysentery,
with abundant blood and mucus in the stool.
• Eggs may be detected in feces at this time.
• Chronic infection may result in liver fibrosis
and portal hypertension, depending on the
number of worms present.
• Eggs may be more difficult to find in feces
during this stage.
• Eggs, which measure 116–180 μm by 45–58
μm, are oval, with a large distinctive lateral
spine that protrudes from the side of the egg
near one end.
Schistosoma japonicum
• occurs in China, southeast Asia, and the
Philippines, causes disease that is clinically
similar to that of S. mansoni but often more
serious because many more (up to 10 times as
many) eggs are produced by S. japonicum.
• The disease has been essentially eliminated
from Japan, although animal reservoirs still
exist.
• Adult worms live primarily in the distribution of
the superior mesenteric vein, and eggs readily
reach the liver, inducing fibrosis and portal
hypertension as a common complication of
chronic infection.
• The smaller size of the eggs predisposes them to
dissemination, especially to the brain and spinal
cord.
• The eggs are broadly oval, measuring 75–90 μm
by 60–68 μm, and have an inconspicuous lateral
spine, which may be difficult to demonstrate.
Schistosoma haematobium
• Urinary schistosomiasis occurs in many parts
of Africa, the Middle East, and Madagascar.
• Parasites migrate via the hemorrhoidal veins
to the venous plexuses of the urinary bladder,
prostate, uterus, and vagina.
• One of the earliest and most common
symptoms of infection is hematuria,
especially at the end of micturition.
• Chronic infection may cause pelvic pain and
bladder colic, with an increased desire to
urinate.
• Accumulation of eggs in the tissues may result
in hypertrophy of the urothelium, squamous
metaplasia, and marked fibrosis, which may
progress to obstruction and, ultimately, renal
failure.
• Urinary schistosomiasis also has been
associated with squamous cell carcinoma of
the bladder.
• Eggs are recovered from the urine by
examination of spun sediment.
• They are elongate, measuring 112–180 μm by
40–70 μm, and have a characteristic terminal
spine.
DIAGNOSIS
• Definitive diagnosis of schistosomiasis
requires the recovery of the characteristic
eggs in urine, stool, or biopsy specimens.
• In S haematobium infections, eggs are most
numerous in urine samples obtained at
midday, especially the last drops voided.
• Cystoscopy with biopsy of the bladder mucosa
may be required for the diagnosis of mild
infection.
• Eggs of S mansoni and S japonicum are
passed in the stool.
• Results of rectal biopsy may be positive when
those of repeated stool examinations are
negative.
• Conventional serologic tests detect circulating
antibodies with sensitivities exceeding 90%,
but cannot distinguish active from inactive
infection
• Enzyme immunoassay (EIA)- based reagent
strip (dipstick) tests, capable of detecting
circulating, genus-specific, adult worm
antigens in blood and urine, are rapid, simple,
and sensitive.
• They are particularly helpful in the diagnosis
of Katayama syndrome in those returning
from endemic areas.
• because antigen levels drop rapidly after
successful therapy, these tests may prove
helpful in distinguishing active from inactive
disease.
TREATMENT
• Praziquantel, which is active against all three
species of schistosomes, is the agent of
choice.
prevention
• Prevention involves proper disposal of human
waste and eradication of snail host when
possible.
• Swimming in areas of endemic infection
should be avoided.