The Parasitic Infections of Humans (Part 3 - Trematodes).pdf

MicroPara

1. THE PARASITIC INFECTIONS
OF HUMANS
Prepared by: Renz Victor T. Guangco, M.D.
PART III: HELMINTHIC INFECTIONS - TREMATODES

2. THE TREMATODES
•Trematodes, commonly known as flukes,
belong to the class Trematoda or Digenea.
•They may be hermaphroditic or dioecious
(reproduce via separate sexes).
•Morphologically, flukes are fleshy, leaf
shaped worms.
•Unlike tapeworms, flukes have a digestive
tract.

3. THE TREMATODES
•In general, flukes have two muscular suckers:
•An oral type, which is the beginning of an
incomplete digestive system
•Ventral sucker which serves for
attachment.
•The eggs of the trematodes vary in
appearance and are the primary morphologic
stage that are usually recovered from
humans.
•Some eggs may possess a lid like structure
that can flip open to release its contents
(operculum)

4. THE TREMATODES
•Unlike in cestode infections, humans never serve
as intermediate hosts for the flukes.
•In general, flukes have two intermediate hosts
except for the blood flukes where there is only one
intermediate host.
•Common to all trematodes, the first intermediate
hosts are mollusks(snails and clams) where asexual
reproduction takes place.
•The second intermediate host varies depending on
the parasite. Sexual reproduction of flukes occurs
in humans.
•In most cases, humans acquire the infection
through ingestion of undercooked or raw second
intermediate host.

5. THE TREMATODES
•Three schistosomes are frequently associated with
human disease, namely:
•Schistosoma mansoni
•Schistosoma japonicum
•Schistosoma haematobium
Schistosoma spp. (Blood Dwelling Flukes)

6. THE TREMATODES
•Known as the “romantic parasites,” the male and
female worms are usually in a state of copulation
(en copula).
•Blood flukes are dioecious. Female worms are
usually larger than the male worms.
•The schistosomes are also obligate intravascular
parasites.
Schistosoma spp. (Blood Dwelling Flukes)

7. THE TREMATODES
•The eggs are found in fresh water contaminated
with the feces or urine of infected humans.
•Once in the water, eggs develop into a miracidium,
that will then locate a snail as its host, where it
transforms into cercariae.
•Infection is acquired through skin penetration by
the fork tailed cercaria (larval form).
Schistosoma spp. (Blood Dwelling Flukes)

8. THE TREMATODES
•The parasite migrates into the bloodstream where
they undergo maturation.
•The location of the adults varies by species.
•Schistosoma japonicum localize in the
superior and inferior mesenteric and portal
vein and
•Schistosoma mansoni localize in the inferior
mesenteric vein
•Schistosoma haematobium worms localize in
the veins surrounding the urinary bladder.
Schistosoma spp. (Blood Dwelling Flukes)

9. THE TREMATODES
•Schistosoma mansoni and Schistosoma
haematobium are both distributed throughout
Africa.
•S. mansoni is also found in South America while S.
haematobium is also prevalent in the Middle East.
•Schistosoma japonicum is endemic in Indonesia,
some parts of China, and Southeast Asia, including
the Philippines.
•It is the only schistosome for which domestic
animals (e.g., water buffalo and pigs) act as
important reservoirs.
Schistosoma spp. (Blood Dwelling Flukes)

10. THE TREMATODES
•Most of the findings are caused by the presence of
eggs in the liver, spleen, or walls of the gut or the
urinary bladder, depending on which species is
causing the infection.
•Eggs of S. japonicum in the liver may induce
granuloma formation leading to fibrosis and portal
hypertension, as well as damage the walls of the
small and large intestines.
•Eggs of S. mansoni may damage the walls of the
distal colon.
•Eggs of S. haematobium may induce granuloma
and fibrosis in the walls of the urinary bladder
Schistosoma spp. (Blood Dwelling Flukes)

11. THE TREMATODES
Schistosoma spp. (Blood Dwelling Flukes)

12. THE TREMATODES
•Most of the findings are caused by the presence of
eggs in the liver, spleen, or walls of the gut or the
urinary bladder, depending on which species is
causing the infection.
•Eggs of S. japonicum in the liver may induce
granuloma formation leading to fibrosis and portal
hypertension, as well as damage the walls of the
small and large intestines.
•Eggs of S. mansoni may damage the walls of the
distal colon.
•Eggs of S. haematobium may induce granuloma
and fibrosis in the walls of the urinary bladder
Schistosoma spp. (Blood Dwelling Flukes)

13. THE TREMATODES
Disease: Schistosomiasis (Bilharziasis)
•Asymptomatic infection – the most common form of the
disease. Chronic infection may become symptomatic.
•Early acute infection – characterized by pruritic papules
seen at the site of entry of the parasite.
•This is called “swimmer’s itch” or “clam digger’s itch.”
This is followed after 2–3 weeks by fever and chills,
abdominal pain, cough, bloody diarrhea, and weight
loss.
•Painful urination(dysuria) and blood in the urine
(hematuria) may also occur in patients infected with S.
haematobium.
Schistosoma spp. (Blood Dwelling Flukes)

14. THE TREMATODES
Disease: Schistosomiasis (Bilharziasis)
•Katayama fever – a systemic hypersensitivity reaction to the
migrating schistosomes, usually associated with S. japonicum.
•It is characterized by a rapid onset of fever, myalgia, body
malaise, cough, diarrhea, and eosinophilia occurring 1–2
months after exposure to the parasite.
•Swollen lymph nodes (lymphadenopathy) and enlargement
of the liver and spleen (hepatosplenomegaly) may also
occur.
•It can lead to hepatic dysfunction, leading to portal
hypertension.
•The most common cause of death in this case is internal
bleeding from ruptured esophageal varices.
Schistosoma spp. (Blood Dwelling Flukes)

15. THE TREMATODES
Disease: Schistosomiasis (Bilharziasis)
•Associated conditions – include developmentof
nephrotic syndrome in S. japonicum and S.
haematobium infection.
•Infection with S. mansoni or S. japonicum may
predispose to repeated Salmonella infections.
•S. japonicum is associated with the development
of hepatocellular carcinoma or liver cancer
•S. haematobium has been implicated in the
developmentof cancer of the urinary bladder.
Schistosoma spp. (Blood Dwelling Flukes)

16. THE TREMATODES
•There are three morphologic stages of the parasite—
egg, larva, and adult.
•The egg have an operculum surrounded by a thick rim
called the shoulder.
•The first intermediate host is the freshwater snail while
the second intermediate host is a freshwater fish.
•Within the egg is the developed miracidium, that is
released once the egg comes into contact with fresh
water
Clonorchis sinensis (Chinese Liver Fluke)

17. THE TREMATODES
•The miracidium penetrates the first intermediate host and
develops into a sporocyst that contains numerous larval
stages called the rediae.
•The larvae are then released into the water where they
transform into cercariae.
•The cercariae enter a freshwater fish where they encyst to
become the metacercariae.
•The larvae excyst in the duodenum, enter the biliary ducts, and
differentiate into adults.
•The adult worms produce eggs that are excreted in the feces.
•Humans acquire the infection by ingesting raw or undercooked
freshwater fish containing the infective metacercariae.
Clonorchis sinensis (Chinese Liver Fluke)

18. THE TREMATODES
Clonorchis sinensis (Chinese Liver Fluke)

19. THE TREMATODES
•Clonorchis sinensis is found in Asia including Korea,
China, Taiwan, Vietnam, Japan, and Asian Russia.
•The parasite does not usually cause significant lesions,
however, parasites that inhabit the bile ducts can
damage the biliary tract.
•Patients who develop infection with the parasite are at
higher risk of developing cholangiocarcinoma or cancer
of the bile ducts.
•The egg has also been associated with the
development of gallstones (stones in the gall bladder or
cholelithiasis).
Clonorchis sinensis (Chinese Liver Fluke)

20. THE TREMATODES
Disease: Clonorchiasis
•Most patients are asymptomatic.
•In heavy worm burden, patients may manifest a fever,
upper abdominal pain, anorexia, hepatomegaly,
diarrhea, and eosinophilia.
•Liver dysfunction may also occur in chronic infection
associated with heavy worm burden.
Clonorchis sinensis (Chinese Liver Fluke)

21. THE TREMATODES
Laboratory Diagnosis
•Diagnosis is established by finding the characteristic
eggs in stool specimen or duodenal aspirates.
Clonorchis sinensis (Chinese Liver Fluke)

22. THE TREMATODES
•The Fasciola hepatica eggs possess an operculum similar to
Clonorchis sinensis and is also equipped with shoulders.
•The first intermediate host for the parasite is the snail while
the second intermediate hosts are edible aquatic plants
(kangkong and watercress).
•Humans acquire the infection by ingesting raw edible aquatic
plants or by drinking water contaminated by metacercariae
(infective stage).
•Upon ingestion, the metacercaria eexcyst in the duodenum or
jejunum, releasing the young flukes. These young flukes
wander over the viscera until they reach the liver capsule.
•The adult worms (pathogenic stage) live in the biliary
passages of the liver.
Fasciola hepatica (Sheep Liver Fluke)

23. THE TREMATODES
•Immature eggs are carried by the bile into the intestines and
subsequently excreted with feces.
•The eggs mature in the water and infect the first intermediate
host.
•The cercariae escape the snail host, usually at night, then
encyst on the surface of aquatic plants, forming metacercariae.
•The natural host for the completion of the life cycle is the
sheep, however the parasite may also be found in cattle.
•In sheep raising countries, ingestion of raw sheep liver
containing the adult worm also serves as an additional mode of
transmission.
•Humans serve as accidental hosts.
Fasciola hepatica (Sheep Liver Fluke)

24. THE TREMATODES
Fasciola hepatica (Sheep Liver Fluke)

25. THE TREMATODES
•The Fasciola hepatica is found worldwide, especially
in sheep and cattle raising countries, and where
humans consume raw watercress such as Asia,
Europe, and the Middle East.
•The stages of the disease correspond with the
migration of the parasites.
•The acute or invasive phase corresponds to the
migration of the parasite through the liver
parenchyma, which leads to traumatic and necrotic
lesions in the liver.
Fasciola hepatica (Sheep Liver Fluke)

26. THE TREMATODES
•The severity of the destruction is proportional to the
number of metacercariae ingested.
•The chronic phase corresponds to the localization of
the adult worms to the bile ducts.
•The worm can obstruct the bile duct and stimulate
inflammation.
•During migration from the intestines to the liver, the
parasite may wander to other sites (e.g., lungs,
subcutaneous tissues, brain, or orbit) where
abscesses may develop
Fasciola hepatica (Sheep Liver Fluke)

27. THE TREMATODES
Disease: Fascioliasis or Sheep Liver Rot
•Migration of the larval worm through the liver irritates the
organ, manifesting as tenderness and hepatomegaly.
•Characteristic clinical features include right upper
quadrant pain, fever and chills, and marked eosinophilia.
•Hepatitis may develop with biliary obstruction.
•Some worms may cause necrotic foci in the liver.
•Ingestion of raw sheep liver may lead to temporary
lodgment of the adult worm in the pharynx leading to
suffocation.
Fasciola hepatica (Sheep Liver Fluke)

28. THE TREMATODES
Laboratory Diagnosis
•Diagnosis rests on finding of eggs in stool specimen,
•Examination of a sample of the patient’s bile may aid
in the differentiation.
•If the eggs are present in bile then this is indicative of
F. hepatica.
•Other tests that can be performed include ELISA and
the Enterotest
Fasciola hepatica (Sheep Liver Fluke)

29. THE TREMATODES
•Similar to other trematodes, the first intermediate host for
Paragonimus is a snail while the second intermediate hosts
are crabs or crayfish.
•Humans acquire the infection by ingesting raw or
undercooked crabs or crayfish that contain the infective
encysted metacercaria.
•The larva excysts in the small intestines, migrate through the
intestinal wall, through the peritoneal cavity, into the
diaphragm then into the lung parenchyma where they
mature.
Paragonimus westermani (Oriental Lung Fluke)

30. THE TREMATODES
•The adult worms enter the bronchioles and are then
coughed up or swallowed.
•Eggs in the sputum or feces reach fresh water, hatch, and
penetrate the first intermediate host, where they differentiate
into free swimming cercariae.
•The cercariae leave the snail host and encyst in freshwater
crabs that are eaten by humans.
Paragonimus westermani (Oriental Lung Fluke)

31. THE TREMATODES
Paragonimus westermani (Oriental Lung Fluke)

32. THE TREMATODES
Epidemiology and Pathogenesis:
•P. westermani infection occurs most commonly in Asia, in
countries like China, the Philippines, Japan, Vietnam, South
Korea, Taiwan, and Thailand.
•Pigs, monkeys, and other animals that eat crayfish and crabs
serve as reservoir hosts.
•The worms exist in a fibrous capsule within the lung which
communicates with a bronchiole.
•Within this cyst is blood tinged purulent material containing eggs.
•Secondary bacterial infection frequently occurs.
Paragonimus westermani (Oriental Lung Fluke)

33. THE TREMATODES
Disease: Paragonimiasis (Pulmonary distomiasis, Endemic
hemoptysis, Parasitic hemoptysis)
•The early stages of the disease are usually asymptomatic.
•Patients may later experience symptoms related to pulmonary
involvement including cough productive of blood tinged sputum
(hemoptysis), fever, and chest pain.
•The sputum has a foul, fishy odor and is most pronounced in the
morning.
•The disease may mimic pulmonary tuberculosis.
•In rare cases, the immature flukes may migrate to the brain leading to
cerebral paragonimiasis, which may manifest as seizures, visual
disturbances, and reduced motor skill precision.
Paragonimus westermani (Oriental Lung Fluke)

34. THE TREMATODES
Laboratory Diagnosis
•Diagnosis is made by demonstration of the characteristic
eggs in sputum or feces (when sputum is swallowed).
•A chest x ray may be done which may show a ring
shadowed opacity with several contiguous cavities giving
the appearance of a cluster of grapes.
Paragonimus westermani (Oriental Lung Fluke)

35. •END OF DISCUSSION
•Source: Burton’s Microbiology for the Health Sciences, 11th Ed.
•Microbiology and Parasitology, a Textbook and Laboratory Manual for
the Health Sciences, 2nd Ed., by Bartolome and Quiles
•Centers of Disease Control: www.cdc.com