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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