Schistosomes

1. Family Schistosomatidae – Blood Flukes
Chapter 16
Blood flukes belonging to the genus
Schistosoma are important parasites of humans:
●
disease is
____________________________________
●
disease is named after German Theodor
Bilharz who identified adult parasite in the
1851
Schistosomiasis in one of the major parasitic
diseases in the world - 270 million persons are
infected (1 out of every 12 persons).

2. Disease is on the increase in the world because:
1.
2.
3.
4.

3. Schistosomiasis is distributed in parts of the tropics.
It is not endemic in the continental U.S. but does occur in
Puerto Rico and other Caribbean islands.
Cases in U.S.?

4. 3 major species of human Schistosoma
Schistosoma mansoni - adults occur in
the posterior mesenteric veins of
the
__________________________
Schistosoma japonicum - adults occur
in the anterior mesenteric
veins of the
_____________________
Schistosoma haematobium - adults
occur in the veins of the
_____________________________
(There are 2 other minor species in humans we
will not consider.)

5. Morphology of Adult Schistosoma
Schistosoma is ____________________.
Male worms are shorter and stouter than
females.
●
males have
_____________________________
- ventral longitudinal groove in
which the female resides
●
several testes are located behind
the acetabulum

6. Morphology of Adult Schistosoma
Female worms are thin and long –
resides in the gynecophoral canal of male
• reproductive organs are arranged
linearly

Both sexes have oral sucker and
acetabulum.
Intestine (cecum) divides, then fuses near
middle of the body.

7. Morphology of Adult Schistosoma

8. Differences of Adult Schistosoma
Adults of the 3 species differ in:
1.
2.
3.
4.
However, there is overlap of many
characteristics.
We will not be responsible for
identification to species.

9. Differences of Adult Schistosoma

10. Differences of Schistosoma Eggs
Specific diagnosis is determined by ID of eggs
S. mansoni - elliptical egg with
________________________________________
S. haematobium - elliptical egg
________________________________________
S. japonicum - round to oval egg with __________________________________

11. Life Cycle – similar in 3 spp.
1. Adult female enters small
venules in wall of intestine or
urinary bladder and deposits
eggs.
2. Eggs work their way through
the tissue by mechanical action
and reach the lumen.
- Eggs of S. mansoni and S.
japonicum are voided in
_____________________.
- Eggs of S. haematobium are
voided in __________________.
What happens to most eggs?

12. Life Cycle – similar in 3 spp.
3. Eggs embryonate during
passage through the tissues and
hatch soon after eggs are
released into water.
4. _______________________
hatches from egg and swims for
1-6 hours to find a snail
intermediate host.
The three species of
schistosomes utilize 3 different
snail intermediate hosts.
5. Within the snail,
_________________________
develops which produces
_________________________.
(no redia stage)

13. Life Cycle – similar in 3 spp.
6. ______________________
________________________
emerge from daughter
sporocysts and leave the snail.
- Over 200,000 cercariae may
be produced in a snail infected
with a single
miracidium!

14. Life Cycle in Human
.
7. Cercariae swim for 1-3 days until they
find human host.
Cercariae are attracted to human by skin
secretions.
8. On human skin, cercariae release
histolytic enzymes from penetration glands
and ________________________________
A cercaria loses its tail and becomes a
______________________________

9. Schistosomula enter circulation and reach
the liver where they mature to adults.

15. Life Cycle in Human
.10. Adults migrate down the hepatic
portal vein into the mesenteric veins of
intestines or urinary bladder where
they mate and females begin to
produce eggs.
- Egg production begins 5-8 weeks
after cercarial penetration.

17. Differences in Life Cycles of 3 species

18. Schistosoma japonicum
Distribution - Orient (China,
Southeast Asia, Philippines, and
South Pacific Islands)
Adults inhabit the ______________
_____________________________
_____________________________
Adult female is proliferic egg layer -
up to 3,000 eggs are deposited in the
submucosa of the small intestine
daily.

19. Pathology of Schistosoma japonicum
1. Eggs in the _______________
________________________
cause host inflammatory
reaction and fibrous scar tissue
nodules are formed.
- these nodules may ulcerate
and result in hemorrhaging
- some eggs migrate through
the wall to be released in the
feces

20. Pathology of Schistosoma japonicum
1.Eggs are swept up the hepatic
portal vein into the
____________________
- ________________________
occurs around the eggs
- _______________________
- areas of scar tissue form
around eggs
- cirrhosis and
hepatosplenomegaly result

21. Pathology of Schistosoma japonicum
•In 9% of cases, eggs reach the _______________causing
severe tissue reaction resulting in paralysis, coma, and
death.
No pathology is caused by the adults.

22. Pathology of Schistosoma japonicum
Schistosoma japonicum is considered the most pathogenic of the
three species:

1. Produces _______________________
2. Eggs cause greater pathology in ________________
3. Only species in which eggs can enter the ________________

23. Biology of Schistosoma japonicum
Many ______________________________________ serve to maintain the
infection for possible human infection. Other hosts are cattle, pigs, goats,
dogs, cats, deer, and rodents.
Thus, this disease is a ____________________.
CONTROL of S. japonicum is difficult due to:
(1) numerous reservoir hosts
(2) snail intermediate host is
_______________________________
and only visits water to lay its eggs.
Molluscicides are ineffective.

24. Schistosoma mansoni

Distribution - widely distributed in various parts of Africa,
Middle East, South America, and Caribbean Islands

25. Schistosoma mansoni

Adults live in the ___________________________________
_________________________________________________
Female releases eggs into the wall of the large intestine and
eggs work their way into the lumen and are released in the
feces.
Less than 100 eggs are produced each day, but egg deposition
occurs for the life of the worm (4 years up to 26 years).

26. Pathology of Schistosoma mansoni


1. Eggs in the ______________________________________ stimulate host
inflammatory reaction followed by fibrous scar tissue deposition.
●
Fibrous scar tissue forms nodules along the large intestine.
●
Some eggs make their way through the intestine to enter the feces

Inflammatory reaction to eggs Fibrous scar tissue nodules

27. Pathology of Schistosoma mansoni


•Eggs are swept up the hepatic portal
vein into the liver
●
__________________________
is ollowed by scar tissue
formation of
______________________
●
cirrhosis and
hepatosplenomegaly occur

Cirrhosis – areas of
scar tissue in liver

28. Pathology of Schistosoma mansoni


●
___________________________________ (accumulation of fluid in
abdominal cavity) is common
●
This produces the typical "swollen belly" associated with chronic
schistosomiasis

On the left, a boy of 11 shows massive liver and spleen
enlargement. On the right, a boy of 9 in a well advanced stage
of early chronic infection.

29. Pathology of Schistosoma mansoni

No brain involvement as eggs are too big to pass through
the liver.
Again, no pathology is caused by the adults.

Disease is _____________________________ and years may
elapse before the parasite will kill its human host.

Natural infections also occur in monkeys and baboons but
disease is not a zoonosis as humans and primates do not live
together. Thus, it is ________________________________.

30. Schistosoma haematobium

Distribution - through Africa and in parts of the Middle East
Co-exists with ____________________________________ in
much of Africa especially along the Nile River Valley.

31. Schistosoma haematobium

Adults live in the ________________
___________________________
Most eggs pass through the wall of
the urinary bladder and are
voided in the urine.
Invasion of other organs by eggs?
___________________________
Thus, this species is considered to be
the least pathogenic of the 3
species.

32. Pathology of Schistosoma haematobium

1. _____________________________
- eggs in the tissues of the urinary
bladder cause inflammation.
Intense pain occurs at end of
urination.
2. __________________________ -
blood in the urine is common

33. Pathology of Schistosoma haematobium

3. _________________________
deposition around eggs in the
urinary bladder wall is common
and tissues lose their elasticity.
4. Infection also increases the
likelihood of
___________________________

Again, all pathology is caused by the
eggs.
Adults cause no pathology.

34. Biology of Schistosoma haematobium

It is thought that this famous individual was infected with
Schistosoma haematobium.
Who is he?
How could he have gotten it?

35. Biology of Schistosoma haematobium

NO reservoir hosts. This parasite is
_______________________________.
Human infection is a result of infected persons urinating in
ponds, lakes, streams, and irrigation ditches.
Irrigation practices in the Nile River Valley due to the building
of the Aswan High Dam have increased the prevalence
of this parasite from 5% to over 35%.
Movie on S. haematobium in Nigeria:
http://www.cartercenter.org/news/multimedia/HealthPrograms/EndingtheAnguishof
aSilentDisease2008.html

36. Diagnosis of Schistosomiasis
Diagnosis is by
______________________________________________
- this is augmented by use of concentration techniques or
tissue biopsy.
Immunological tests to identify schistosome antigens have
been developed recently and are also effective in diagnosis.
- ELISA test is 100% effective
- most useful when?

37. Treatment of Schistosomiasis
Drugs are available: 1. Antimony compounds
2. Anti-malarial drug Artemisinin
3. Oxamniquine
4. Praziquantel
5. Calcium-channel blockers ?
Drug treatment is difficult when large populations must be treated.
- some drugs are toxic
- all require long-term treatment and constant monitoring
- adults may migrate back into the liver where drugs are less effective
- drugs are expensive
- Praziquantel resistance is now appearing in ____________________
Drug treatment is not effective once liver involvement occurs.

38. Prevention of Schistosomiasis
1.___________________________________
●
Human insistence on pollution of water with their wastes is
difficult to change.
●
People need to know to stay out of infected water
2. ____________________________________ - problems just
mentioned

39. Prevention of Schistosomiasis
3. ______________________________________- avoid contact between
human wastes and water containing snails.
●
Livelihood around water (crop irrigation, fishing, washing clothes,
bathing, etc.) perpetuates schistosomiasis.
●
Costs money to bring clean water into a village

40. Prevention of Schistosomiasis
1.Snail control by use of _______________________________.
●
Application is tricky - too high a dose will kill fish
- too little may not kill all the snails and their
numbers will be back to the same in a few months
●
Not effective against the amphibious snail of S. japonicum
as snail can move onto land away from the molluscicide

41. Prevention of Schistosomiasis
1.Introduction of ____________________________________ –
shown some success

42. Prevention of Schistosomiasis
No vaccine or drug preventative is yet available to prevent
schistosomiasis
Nobel prize is medicine is waiting for someone who can find an
effective vaccine.

43. Immunology of Schistosomiasis
In many parasitic infections, the parasite
or its eggs are detected by our immune
system as being "foreign" (this is an
________________________).
If the antigen (parasite) is too large to be
phagocytized, the host immune
system attacks this foreign invader by
producing inflammation and fibrous scar
tissue around the parasite or its eggs to
"wall it off" from other tissues.
This occurs in schistosome eggs, liver
fluke infection, and lung fluke infection.

44. Immunology of Schistosomiasis
Adult schistosomes live within the bloodstream and are in
constant contact with host lymphocytes which detect antigens
and start the immune response.
Why aren't adult schistosomes detected?

45. Immunology of Schistosomiasis
Adults have the ability to acquire
______________________________________
(proteins in the bloodstream) and coat their _______________
with these molecules.
This coating takes 3 days but once it is accomplished, the
parasite is recognized by lymphocytes as “a human cell" and is
protected from a host immune response.
As a result, they are not detected by the immune system and
no pathology is caused by the adults.

46. Swimmer’s Itch
Swimmer's itch is caused by _____________________________
____________________________________________________
Swimmer's itch is common in Midwest and along coastal areas of
the U.S.
- itch was first described at U. Michigan Biological
Station in 1936
- extensively studied in Wisconsin
in the 1930's & 40’s
- problem is common in Wisconsin
lakes and occasional outbreaks occur
(recent outbreak in Half Moon Lake
in Eau Claire)

47. Swimmer’s Itch
3 genera of schistosomes cause swimmer's itch in the Midwest:
Gigantobilharzia - adult blood flukes occur in mesenteric
veins of ____________________________________
Trichobilharzia - adults in mesenteric veins of
_________________________________
Schistosomatium - adults in mesenteric veins of
_________________________________

48. Life Cycle

49. Life Cycle of Swimmer’s Itch
Humans become infected when snail
intermediate hosts of these parasites
release_________________________which
mistake humans for the definitive host.
Infection results when __________________
_____________________________________

Snail hosts are common pond snails in the
genera Physa and Lymnaea.

50. Pathology of Swimmer’s Itch
Cercariae penetrate epidermis but are
unable to enter the dermis.
Cercariae die in the epidermis and an
______________________________
is produced against the dead cercariae
Formation of a
____________________________
(dermatitis) occurs at the sites of
cercarial penetration.
Intense itching also occurs.

51. Pathology of Swimmer’s Itch
Dermatitis is mild in initial
exposures but may become
severe in persons exposed to
previous outbreaks – called
_______________________
Itching and breaking of skin
may lead to secondary
infections.
Rash has been misdiagnosed
as the
______________________

52. Treatment and Prevention of Swimmer’s Itch
TREATMENT - topical creams such as
___________________________ reduce the itching
and ______________________________ reduce
the inflammatory response
PREVENTION – best way to reduce swimmer’s
itch is to
__________________________________________
__________________________________________
●
Snail control efforts (using copper sulfate as
molluscicide) have been attempted but
generally have been unsuccessful.
●
Removal of bird or mammal definitive hosts
is not possible.

53. Swimmer’s Itch
Swimmer's itch is a problem to _________________________
__________________________________________________
- Swimming beaches are common sources of infection.
- First outbreaks occur in late June and early July when
vacationers are numerous.
But problem is often kept hushed,
as resort owners don’t want you to
know that swimmer’s itch is a
problem in their lake, as they
don’t want to lose business.