TREMATODES

 Kingdom: Anemalia  Heterophyes and Metagonimus are two species of minute

(1–3 mm in length) intestinal worms that infect humans.
 Phylum: Platyhelminthes
 the hermaphroditic flukes produce operculate eggs, which
 Superclass: Neodermata are not embryonated.
 Class: Trematoda  Infections are acquired by ingestion of metacercariae in raw
 Subclass: Digenia or incompletely cooked freshwater fish except for F. buski.

The trematodes are parasites of mollusks and vertebrates. Fasciolopsis buski

The Digenea, the majority of trematodes, are obligate Largest intestinal trematode (20-75 mm in length and 8-20
parasites of both mollusks and vertebrates, but rarely occur in mm)
cartilaginous fish. Infection is by ingesting infectious metacercariae on aquatic
Two other parasitic classes: food plants such as water chestnuts and water caltrop.
1. Monogenea
2. Cestoda

 Worms

Classification of flukes according to the environment in

which they are found:

 Intestinal flukes
 Lung flukes
 Liver flukes attach to the wall of the duodenum
 Blood flukes and jejunum, where they mature to
Adult Trematodes egg-laying adults in about 3 months.
Clonorchis Chinese or oriental
 Symptoms: diarrhea, epigastric pain,
sinensis liver fluke
and nausea.
Opisthorchis Cat liver fluke
felineus  Eosinophilia may be present, even in
Metorchis Canadian liver fluke those who are asymptomatic.
conjunctus
Metagonimus Minute intestinal fluke
yokogawai
Nanophyetus Intestinal fluke of fish
salmincola eating mammal
Paragonimus Lung fluke
westermani
Fasciola hepatica Liver fluke or sheep liver
fluke
Fasciolopsis buski Largest intestinal fluke

Intestinal Flukes
 include Fasciolopsis, Heterophyes and Metagonimus,
Nanophyetus,

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 Fasciolopsis buski Life Cycle Metagonimus yokogawai Life Cycle

Heterophyes and Metagonimus

These two genera include a number of species of minute (1–3

mm in length) intestinal worms that infect humans:
a. Heterophyes heterophyes
b. Metagonimus yokogawai

 Infections are acquired by ingestion of metacercariae in

raw or incompletely cooked freshwater fish

 Infection with these worms may produce diarrhea and

abdominal pain

 Infections are self-limited because the worms have a life

span of only a few months.

Heterophyes heterophyes Life Cycle

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 DIAGNOSIS

- finding the embryonated, operculate eggs (20-30 μm in Echinostomiasis

length by 15-17 μm in width)
Causal Agent:
- differentiation of these eggs from those of Clonorchis and
Opisthorchis is difficult, although the operculum is more  Trematodes in the genus, Echinostoma.
deeply seated with Opisthorchis  The genus is worldwide, and about ten species have been
recorded in humans, including E. hortense, E. macrorchis,
E. revolutum, E. ilocanum and E. perfoliatum.
Echinostoma ilocanum

 Garrison’s fluke

 widespread among the Philippine

Nanophyetus salmincola Islands but only 3% of over
30,000 stools were found to be
 small (0.8-1.1 mm) intestinal fluke that has
positive for eggs.
been reported in humans.
 The prevalence rates were
 these worms are acquired by ingesting raw,
highest in the population of
incompletely cooked, or home-smoked
Ilocos region in northern Luzon;
salmon that contain infectious
11% of over 7,000 stools
metacercariae.
examined, however, rates as high as 44% were found.
 occurrence of symptoms is related to the
Echinostoma Life Cycle
number of worms present and may include
abdominal pain and diarrhea, with or
without eosinophilia
Nanophyetus salmincola Life Cycle

Liver Flukes

Diagnosis  include Clonorchis, Opisthorchis, and Fasciola.

- eggs (60-80 μm by 34-50 μm) are broadly ovoid, operculate,  Clonorchis and Opisthorchis are considered the most
and yellowish brown important human pathogens because they are classified as
class 1 carcinogens.
Note: This fluke is the vector for a rickettsia that produces a
highly lethal infection in cannes known as ‘salmon-poisoning’  Liver flukes are commonly found within bile ducts, liver,
disease. and gallbladder in mammalian and avian species.

 There are high numbers of human infection with all three

of these liver flukes.

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 Fasciola gigantica Life cycle

Fasciola hepatica

Key points:

 liver fluke
 Infects cattle, sheep, and goats
 adult parasites : biliary tree and lay eggs that are passed in
the feces
 Cercariae > shed from snail intermediate host > encyst on
aquatic vegetation > metacercariae > available to
herbivorous hosts
 humans usually acquire the infection by eating watercress
 Once ingested > larvae penetrate the intestinal wall >
migrate through the peritoneal cavity to the liver > burrow
through the capsule and parenchyma > reside within the
bile ducts, lays eggs (initiated in about 2 months) >
larval migration > liver > bile duct (elicits a painful
inflammatory reaction which become fibrosed)

clinical manifestations:

colic, obstructive jaundice, tenderness, cholelithiasis, and

eosinophilia.
Diagnosis:

- eggs in the stool (unembryonated -

yellowish brown, operculate eggs (130-
150 μm by 63-90 μm) cannot easily be
distinguished from those of Fasciolopsis

- spurious infections - occur by ingesting

infected cattle or sheep liver, are
diagnosed by obtaining a good history
and performing a follow-up stool
examination to look for elimination of
the eggs.
Fasciola hepatica Life Cycle Intermediate hosts
Fasciola gigantica

 regarded as one of the most important single

platyhelminth infections of ruminants in Asia and Africa.
 causes outbreaks in tropical areas of southern Asia,
Southeast Asia, and Africa.
 The geographical distribution:
- overlaps with F. hepatica in many African and Asian
countries, in such cases the ecological requirement of the
flukes and their snail host are distinct.

 Infection is most prevalent in regions with intensive

sheep and cattle production.
 eggs (transported with feces) → eggs hatchs →
miracidium → miracidium infect snail intermediate host
→ sporocyst → redia → daughter redia → cercaria →
(gets outside the snail) → metacercaria → infection of
the host → adult stage produces eggs.
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 develop in a molluscan IH  Infections are often asymptomatic, although large
 freshwater snails: numbers of flukes and repeated infections may cause
Lymnaeidae (L. rufescens) inflammation of the bile ducts and subsequent
Radix auricularia hyperplasia, fibrosis, and hepatic cirrhosis.
 Development of cholangiocarcinoma has been linked
Hosts epidemiologically with longstanding infections.
 Fasciola gigantica is a causative agents (together with
Fasciola hepatica) of fascioliasis in ruminants and in Clonorchis sinensis Life cycle
humans worldwide.
 The parasite infects cattle and buffalo and can also be
seen regionally in goats, sheep, and donkeys. Opisthorchis viverrini Life cycle
Infection
 Fasciolosis
- occurs when metacercariae are accidentally ingested on raw Diagnosis:
vegetation > exist in the small intestine > move through the - stool exam: ova - small brown,
intestinal wall and peritoneal cavity > liver where adults embryonated, operculate eggs
mature in the biliary ducts > eggs are passed through the bile
ducts > intestine > feces. - both measure 25-35 μm by 12-20 μm and have a prominent,
Identification seated opercula and a small knob at the abopercular end
No direct coprological (excretion-related) nor an indirect - these eggs are difficult to differentiate from those of the
immunological test available for their diagnosis (F. hepatica Heterophyes/Metagonim us group.
to F. gigantica).
The specific differentiation can only be made by either a - when specific identification is
morphological study of adult flukes or by molecular tools. not possible, the laboratory report
Clonorchis sinensis should reflect
and Opisthorchis viverrini “Clonorchis/Opisthorchis /Heterophyes/M
etagonimus eggs”
 Oriental liver fluke
 closely related species, Opisthorchis viverrini Lung Flukes
 inhabit the biliary system of humans and other animals,  there are eight species of lung flukes that infect humans:
including cats and dogs Paragonimus westermani, P. heterotremus, P. skryabini ,
 acquired by the ingestion of infectious metacercariae in P.miyazakii, P.africanus, P.uterobilateralis, P.kellicotti &
raw or uncooked freshwater fish. P.mexicanus.

 Paragonimus westermani needs three different hosts in

order to survive, reproduce, and complete its life cycle.

 The completion of a lung fluke's life cycle follows the cycle

of first, second, and final hosts.

 The first intermediate host of the lung fluke is a snail, the

second intermediate host is a crab or crayfish, and the
final host for lung flukes is an animal or human host.

Paragonimus spp.
Key points:

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 parasitize the lungs of cats, dogs, and other carnivores, - the operculate, unembryonated eggs (80-120 μm by 45-70
including humans μm) and have a moderately thick, yellow-brown shell

 Known species: - the operculum is flattened and usually is set off from the
rest of the shell by prominent shoulders.
Paragonimus westermani - problematic in many areas of
Asia

Paragonimus mexicanus, Paragonimus caliensis, and

Paragonimus ecuadoriensis. Paragonimus kellicotti – in
Central, South, and North America

Adult worms measure up to 12 mm by 6 mm and often are

found in pairs in lung parenchyma where they reside.

 snail serves as the

first intermediate
host

 freshwater crabs
or crayfish serve
as second
intermediate host
for the infectious
metacercariae.

 Ingestion of uncooked, or marinated, crustacea may result

in infection > larvae are released in the stomach > migrate
through the intestinal wall > peritoneal cavity > reaching
the lungs after penetrating the diaphragm.

 Maturation takes approximately 5-6 weeks, and worms

may live for many years.

Symptoms:

 - onset of lung infection is associated with fever, chills, and

the appearance of eosinophilia

 - chronic coughing with abundant mucus production, and

episodes of hemoptysis.

 - eggs remaining in the lung tissues or in ectopic sites may

cause extensive granulomatous reaction
DIagnosis

radiographs - nodular shadows, calcifications, or patchy

infiltrates

stools, sputum or tissues - finding of typical eggs

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 Blood Flukes
 include five species of Schistosoma: Schistosoma
japonicum, S. mekongi, S. mansoni, S. haematobium, and
S. intercalatum.

 When examined in situ,

schistosomes are often
found in copula. In their
preferred locations,
blood flukes elicit little or
no inflammatory
response.
 Eggs are deposited in the
smallest venule that can
accommodate the female
worm, where they elicit a
strong granulomatous
response that results in
extrusion of the egg into
the intestinal lumen or the bladder.
 Pathology is primarily related to the sites of egg
deposition, numbers deposited, and host reaction to egg
antigens.
 Humans get infected by the cercariae, which are the larval
 Eggs are fully embryonated when passed
forms of trematodes.
and readily hatch when deposited in
 Any contact with water can cause potential human fresh water
infection.
 The miracidia penetrate an appropriate species of snail
 Adult blood flukes can live indefinitely in human or animal host, where they undergo transformation and extensive
reservoir hosts. asexual multiplication
Schistosoma spp.  After about 4 weeks, large numbers of fork-tailed
cercariae emerge from the mollusk.
 Schistosomiasis, or bilharzia, is among the most important
parasitic diseases worldwide  Cercariae swim actively about for hours and
readily penetrate the skin of susceptible
 Adult male and female blood flukes inhabit veins of the hosts, including humans.
mesentery or bladder  After penetration, the cercariae, now called
schistosomules, enter the circulation and pass through
the lungs before reaching the mesenteric-portal vessels.
 The most important species infecting humans are: Symptoms result primarily from:
a. Schistosoma mansoni - penetration of cercariae (cercarial
dermatitis)
b. Schistosoma japonicum
- initiation of egg laying (acute
c. Schistosoma mekongi
schistosomiasis or
d. Schistosoma haematobium Katayama fever)

e. Schistosoma intercalatum - as a late-stage

complication of tissue proliferation and repair
 Adult female schistosomes are slender, measuring up to (chronic schistosomiasis)
26 mm by 0.5 mm.
 Males, which are slightly shorter, enfold a female using - in a matter of hours after cercarial penetration, a papular
the lateral margins of the body (the gynecophoral canal) rash associated with pruritus may develop
to assist in sperm transfer. - Cercarial dermatitis or swimmer's itch occurs worldwide
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- initiation of egg laying by mature worms 5-7 weeks after - feces mixed with distilled water are placed in a flask that is
infection may result in acute schistosomiasis, or Katayama covered with foil to keep out light, with only the neck or a
fever, a serum-sickness-like syndrome that occurs with heavy sidearm exposed to a bright light
primary infections, especially those of S. japonicum.
Serologic tests:

- helpful in screening persons who have traveled to

endemic areas, those with negative urine or stool
examinations who are at risk for infection, or for monitoring
response to therapy

Chronic infection - generally, serologic testing varies with the antigens

used and test methodologies employed
- results in continued egg deposition, many of
which remain in the body - CDC uses the Falcon assay screening test in a kinetic
enzyme-linked immunosorbent assay (FAST-ELISA)
- granulomas produced around these eggs in the
intestine and bladder are gradually replaced by - sera that are positive by the screening test are
collagen, resulting in fibrosis and scarring further evaluated by immunoblot to improve specificity

- eggs trapped in the liver may induce pipe-stem fibrosis with Schistosoma mansoni
obstruction to portal blood flow.
 occurs in Africa, especially in the tropical areas and
Schistosoma spp. Life cycle 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, 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

 If the spine is not visible, the egg may be rotated by

DIagnosis gently tapping the coverslip
- established by demonstrating eggs in feces or urine by direct  Movement of the miracidium within the egg may be
wet mount or formalin–ethyl acetate concentration methods evident in unfixed material if the larva is viable
- Zinc sulfate concentration is not satisfactory for recovery of  Concentration techniques may be required to detect eggs,
the heavy schistosome eggs because individuals with limited exposure or with chronic
infection may pass few of them.
- eggs also may be detected in biopsies of rectal, bladder and,
occasionally, liver tissues either by crush preparation or in
histologic section

- use of egg hatching methods may occasionally be requested

to determine viability or, less commonly, to detect light
infections

Page 8 of 9
  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 examining a spun

sediment (are elongate, measuring 112-180 μm by 40-70
μm, and have a characteristic terminal spine; occasionally,
they may be detected in feces or in a rectal biopsy)

Schistosoma intercalatum
 This species occurs in many parts of
central and western Africa and produces
intestinal schistosomiasis

 Eggs have a terminal spine and so

resemble those of S. haematobium, but
they occur primarily in the feces and are
Schistosome adult larger (140-240 μm by 50-85 μm).
Schistosoma japonicum Schistosoma mekongi
 occurs in China, Southeast Asia, and the Philippines,  occurs in humans and animal reservoirs in countries along
causes disease that is clinically similar to that of S. the Mekong River, especially Cambodia and Laos
mansoni but often more serious because many more (up
to 10 times as many) eggs are produced by S. japonicum.  similar to S. japonicum but is differentiated
from that species by several biological
 the disease has been essentially eliminated from Japan, characteristics and smaller eggs (60-70 μm
although animal reservoirs still exist by 52-61 μm), which otherwise are
 adult worms live primarily in the distribution of the indistinguishable from those of S.
superior mesenteric vein, and eggs readily reach the liver, japonicum.
inducing fibrosis and portal hypertension as a common Schistosome dermatitis
complication of chronic infection.
 swimmer’s itch or clam diggers itch
 The smaller size of the eggs
predisposes them to dissemination,  caused by Schistosome cercaria of
especially to the brain and spinal certain avian and mammalian hosts
cord. The eggs are broadly oval, which penetrate the skin of man but
measuring 75-90 μm by 60-68 μm, can not go any further
and have an inconspicuous lateral
spine, which may be difficult to  destroyed in the skin producing a
demonstrate. dermatitis.

Schistosoma haematobium
 urinary schistosomiasis

 parasites migrate via the hemorrhoidal veins to the

venous plexuses of the urinary bladder, prostate, uterus,
and vagina

 1of the earliest and most common symptoms of infection

is hematuria, especially at the end of micturition
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