Pharmacotherapy of Schistosomiasis
PST 06106
Basic Pharmacotherapy
Session 13: Pharmacotherapy of Schistosomiasis
Learning tasks
By the end of this session students are expected to be able to:
Define
schistosomiasis
Explain pathophysiology of schistosomiasis
Explain the clinical presentation of schistosomiasis
Outline diagnosis of schistosomiasis
Describe pharmacological treatment of schistosomiasis
Describe monitoring of schistosomiasis therapy
Activity: Buzzing
What
is
Schistosomiasis
?
Definition of Schistosomiasis
Schistosomiasis
Schistosomiasis is an acute and chronic parasitic disease caused by blood flukes (trematode worms) of the genus
Schistosoma
.
Definition of Schistosomiasis
Cont
…
There are 2 major forms of schistosomiasis which are intestinal and urogenital caused by 5 main species of blood fluke as follows
;
Definition of Schistosomiasis
Cont
….
Infection happens when larval forms of the parasite released by freshwater snails penetrate the skin during contact with infested water.
Transmission occurs when infected individual from schistosomiasis contaminate freshwater sources with their excreta containing parasite eggs, which hatch in water.
In the body, the larvae develop into adult
schistosomes
.
Adult worms live in the blood vessels where the females release eggs.
Some of the eggs are passed out of the body in the
faeces
or urine to continue the parasite’s lifecycle.
Others become trapped in body tissues, causing immune reactions and progressive damage to organs
.
Pathophysiology and Symptoms of Schistosomiasis
In schistosomiasis, adult worms reside in the mesenteric and pelvic venules in various sites where they lay eggs
These sites tend to be specific for each species (e.g.
S.
japonicum
prefers the superior mesenteric veins draining to the small intestine, while
S.
mansoni
prefers the superior mesenteric veins of the large intestine)
Many eggs are carried upstream where they get lodged in various organs, especially in the liver, bowel, and genitourinary tract
Acute disease may trigger a cell-driven inflammatory response (involving tumour necrosis factor, interleukin-1, and interleukin-6 cytokines) and cause febrile illness
Pathophysiology and Symptoms of Schistosomiasis
Cont..
As mature female worms lay eggs, products of worm and egg metabolism induce formation of immune complexes resulting to a serum like-sickness called Katayama syndrome
In chronic disease, eggs are the cause of pathology; they evoke a Thelper type 2 (Th2) cell-driven granulomatous reaction (involving interleukin-4, interleukin-5, and interleukin-13 cytokines) resulting in tissue fibrosis and chronic morbidity
Gastrointestinal schistosomiasis due to S.
mansoni
, S.
japonicum
and S.
mekongi
can cause bowel lesions such as ulceration,
pseudopolyps
(masses of scar tissue during healing), and
microabcesses
.
These manifest clinically as abdominal pain, altered bowel habits, and blood in stools
Pathophysiology and Symptoms of Schistosomiasis
Cont
…
The
classic sign of urogenital schistosomiasis is haematuria and is specifically noted with
S.
haematobium
Bladder, ureter fibrosis and kidney damage are sometimes seen in advanced cases
The urogenital form may present with genital lesions (e.g. vulvar nodules), vaginal bleeding,
dyspareunia(painful intercourse) ,
and fallopian tube damage (in the late stages) in females
Genital infection in males may
result in
damage to seminal vesicles, prostate and other related organs; this may lead to irreversible infertility
Clinical Presentation of Schistosomiasis
Symptoms of schistosomiasis are caused by the body’s reaction to the worms' eggs.
Intestinal schistosomiasis can result in abdominal pain,
diarrhoea
, and blood in the stool.
Liver enlargement is common in advanced cases, and is frequently associated with an accumulation of fluid in the peritoneal cavity and hypertension of the abdominal blood vessels.
In such cases there may also be enlargement of the spleen.
The classic sign of urogenital schistosomiasis is
haematuria
(blood in urine).
Clinical Presentation of Schistosomiasis
Cont
…
Fibrosis of the bladder and ureter, and kidney damage are sometimes diagnosed in advanced cases.
Bladder cancer is another possible complication in the later stages. In women, urogenital schistosomiasis may present with genital lesions, vaginal bleeding, pain during sexual intercourse, and nodules in the vulva.
In men, urogenital schistosomiasis can induce pathology of the seminal vesicles, prostate, and other organs.
This disease may also have other long-term irreversible consequences, including infertility.
Diagnosis of Schistosomiasis
Schistosomiasis is diagnosed through the detection of parasite eggs in stool or urine specimens
Antibodies and/or antigens detected in blood or urine samples are also indications of infection
For urogenital schistosomiasis, a filtration technique using nylon, paper or polycarbonate filters is the standard diagnostic technique
Children with
S.
haematobium
almost always have microscopic blood in their urine which can be detected by chemical reagent
strips
Diagnosis of
Schistosomiasis
Cont
…
The eggs of intestinal schistosomiasis can be detected in
faecal
specimens through a technique using methylene blue-stained cellophane soaked in
glycerine
or glass slides, known as the Kato-Katz technique
For people living in non-endemic or low-transmission areas, serological and immunological tests may be useful in showing exposure to infection and the need for thorough examination, treatment and follow-up
Activity
: Small Group Discussion
is the
treatment
of Schistosomiasis?
Pharmacological Treatment of Schistosomiasis
The control of schistosomiasis is based on large-scale treatment of at-risk population groups, access to safe water, improved sanitation, hygiene education, and snail control.
The WHO strategy for schistosomiasis control focuses on reducing disease through periodic, targeted treatment with
praziquantel
through the large-scale treatment (preventive chemotherapy) of affected populations.
It involves regular treatment of all at-risk groups.
Groups targeted for treatment are:
School-aged children in endemic areas.
Pharmacological Treatment of
Schistosomiasis
Cont
…
Adults considered to be at risk in endemic areas, and people with occupations involving contact with infested water, such as fishermen, farmers, irrigation workers, and women whose domestic tasks bring them in contact with infested water.
Entire communities living in highly endemic areas.
In high-transmission areas, treatment may have to be repeated every year for a number of years.
Monitoring is essential to determine the impact of control interventions
.
Monitoring Of Schistosomiasis Therapy
Follow-up of treatment response in schistosomiasis needs to be guided by active disease parameters, such as suggestive symptoms, raised eosinophil count, or parasitological/histological evidence of viable eggs
If symptoms such as hematuria or bloody diarrhea persist for weeks after treatment, urine or stool samples should be tested for parasite eggs and appropriate action should be taken depending on the results
Serological assays of the levels of anti-
schistosome
-egg antibodies can also be used in the post-treatment monitoring to confirm
for
treatment
success or failure
from
praziquentel
.
Key Points
Schistosomiasis
is an acute and chronic parasitic disease caused by blood flukes (trematode worms) of the genus
Schistosoma
.
People become infected when larval forms of the parasite are released by freshwater snails and then penetrate the skin during contact with infested water.
Transmission occurs when people suffering from schistosomiasis contaminate freshwater sources with their excreta containing parasite eggs, which hatch in water.
The classic sign of urogenital schistosomiasis is haematuria (blood in urine
Praziquantel is the recommended treatment against all forms of schistosomiasis
Evaluation
What
is Schistosomiasis?
What is the pathophysiology of
Schistosomiasis?
What are the signs and symptoms of Schistosomiasis?
How is the treatment of Schistosomiasis
?
References
Wells
BG,
DiPiro
J,
Schwinghammer
T (2013),
Pharmacotherapy Handbook
(6
th
Ed). New York, NY: McGraw-Hill.
DiPiro
JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey ML, (2008):
Pharmacotherapy: A Pathophysiologic Approach
(7
th
ed
): New York, NY: McGraw-Hill.
Katz M D., Matthias KR., Chisholm-Burns M A., Pharmacotherapy(2011)
Principles & Practice Study Guide: A Case-Based Care Plan Approach
: New York, NY: McGraw-Hill.
Schwinghammer
TL, Koehler JM (2009)
Pharmacotherapy Casebook: A Patient-Focused Approach
(7
th
ed
): New York, NY: McGraw-Hill.
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