2. Introduction
Paragonimiasis is a food-borne parasitic infection
caused by 15 different species of Paragonimus
trematodes
cause a sub-acute to chronic inflammatory disease of
the lung
2
3. P. westermani was discovered in the lungs of a human
by Ringer in 1879
and eggs in the sputum were recognized
independently by Manson and Erwin von Baelz in 1880
3
4. Manson proposed the snail as an intermediate host
and various Japanese workers detailed the whole life
cycle in the snail between 1916 and 1922
The species name P. westermani was named after a
zookeeper who noted the trematode in a Bengal tiger
in an Amsterdam Zoo.
4
5. Epidemiology
Humans become infected after eating raw freshwater
crabs or crayfish that have been encysted with the
metacerciaria.
Southeast Asia is more predominately more infected
because of lifestyles.
Raw seafood is popular in these countries.
Crab collectors string raw crabs together and bring
them miles inland to sell in Taiwan markets.
5
6. These raw crabs are then marinated or pickled in
vinegar or wine to coagulate the crustacean muscle.
This process of cooking does not kill the
metacercariae, consequently infecting the host.
Smashing rice-eating crabs in rice paddies, splashing
juices containing metacercariae, can also transmit the
parasite, or using juices strained from fresh crabs to
medicinal uses.
6
7. This parasite is easily spread because it is able to infect
other animals (zoonosis).
An assortment of mammals and birds can be infected
and act as paratenic hosts.
Ingestion of the paratenic host can lead to infection of
this parasite.
Paragonimus westermani is distributed in southeast
Asia and Japan.
7
8. Other species of Paragonimus are common in parts of
Asia, Africa and South and Central America.
P. westermani has been increasingly recognized in the
United States during the past 15 years
because of the increase of immigrants from endemic
areas such as Southeast Asia.
Estimated to infects 22 million people worldwide.
8
11. Life cycle
The eggs are excreted unembryonated in the sputum,
or alternately they are swallowed and passed with stool
In the external environment, the eggs become
embryonated , and miracidia hatch and seek the first
intermediate host, a snail, and penetrate its soft tissues
11
12. Miracidia go through several developmental stages
inside the snail
sporocysts , rediae , with the latter giving rise to many
cercariae , which emerge from the snail.
The cercariae invade the second intermediate host, a
crustacean such as a crab or crayfish, where they
encyst and become metacercariae.
12
13. This is the infective stage for the mammalian host
Human infection with P. westermani occurs by eating
inadequately cooked or pickled crab or crayfish that
harbor metacercariae of the parasite
13
14. The metacercariae excyst in the duodenum
penetrate through the intestinal wall into the
peritoneal cavity,
then through the abdominal wall and diaphragm into
the lungs,
where they become encapsulated and develop into
adults (7.5 to 12 mm by 4 to 6 mm).
14
15. The worms can also reach other organs and tissues,
such as the brain and striated muscles, respectively.
However, when this takes place completion of the life
cycles is not achieved, because the eggs laid cannot
exit these sites.
Time from infection to oviposition is 65 to 90 days.
15
16. Infections may persist for 20 years in humans. Animals
such as pigs, dogs, and a variety of feline species can
also harbor P. westermani.
16
19. Transmission
Time from infection to oviposition (laying eggs) is 65
to 90 days. Infections may persist for 20 years in
humans.
Humans are infected by eating undercooked
freshwater crabs and crayfish infected with the
metacercariae.
19
20. pathology
The immature flukes burrow out of the human
intestine into the peritoneum, where they mature and
tunnel their way into the lungs.
Here they cause inflammation, haemorrhage, and
necrosis of the lung parenchyma.
Adult flukes (stout, bean-shaped, ~1 cm long) live in
cavities in proximity to airways.
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21. Clinical features
Days-weeks after eating infected food, migration of the
flukes within the peritoneal and pleural cavities causes
signs of inflammatory and allergic responses
fever
rashes
urticaria
abdominal and chest pain or discomfort.
21
22. Ova are expelled either in expectorated sputum or in
the faeces after being swallowed.
Flukes that miss the lungs produce extrapulmonary
symptoms (due to cysts, granulomas, and abscesses) in
muscles, abdominal viscera, brain, genitalia.
22
23. o The classic feature of chronic pulmonary disease is
persistent cough with production of a thick brownish-
red sputum (due to the presence of ova and flukes).
Some times hemoptysis
Physical examination of the chest often reveals little
and the patients appear quite well.
23
24. Aberrant migration of the flukes may produce signs of
a cerebral SOL (epilepsy, raised ICP, psychiatric
syndromes, meningeal irritation) or spinal SOL,
necrosis of abdominal viscera, transitory subcutaneous
swellings.
Extrapulmonary disease may occur in the absence of
pulmonary signs, but this is uncommon.
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25. Ectopic lesions from can involve any organ
including abdominal viscera, the heart, and the
mediastinum.
Paragonimus flukes may also invade the liver, spleen,
intestinal wall, peritoneum, and abdominal lymph
nodes
25
26. In the skin
P. skrjabini often produces skin nodules, subcutaneous
abscesses
a type of creeping eruption known as "trematode larva
migrans."
26
27. In the CNS
The most clinically recognizable ectopic lesions arise
from cerebral paragonimiasis,
which, in highly endemic countries, more commonly
affects children.
Many patients with central nervous system disease
also have pulmonary infections.
CNS involvement occurs in up to 25% of hospitalized
patients
27
28. These children present with
eosinophilic meningoencephalitis,
seizures
or signs of space-occupying lesions.
28
29. Diagnosis:
presence of ova or adult flukes in the sputum, faeces,
or effusion
but these are not present until 2 to 3 months after
infection.
serology.
X-ray the chest cavity and look for worms.
easily misdiagnosed, because pulmonary infections
look like tuberculosis, pneumonia, or spirochaetosis
29
30. Microscopy
Sputum examined microscopically may reveal
Paragonimus eggs released by the flukes in the lungs.
Keep in mind that the acid-fast stain that is used for
TB testing of sputum destroys eggs.
30
31. The eggs may also be found by multiple stool exams on
different days as a result of coughed-up eggs that are
swallowed.
The microscopic eggs are yellowish brown, 80-120 µm
long by 45-70 µm wide, thick-shelled, and with an
obvious operculum.
31
34. Serology and blood tests
Serologic tests can be especially useful for early
infections (prior to maturation of flukes)
or for ectopic infections where eggs are not passed in
stool.
Paragonimus-specific antibody test by micro-ELISA
Peripheral eosinophilia is common and can be intense,
especially during the early larval migration stages.
34
35. lung biopsy
can also be used to diagnose this parasite.
35
37. X-ray the chest
Many patients have a spectrum of abnormalities on chest
radiographs:
lobar infiltrates
coin lesions
cavities
calcified nodules,
hilar enlargement,
pleural thickening and effusions.
37
39. There are typical
fluffy, cotton wool
densities in the right
lung base and left
suprahilar area
produced by the
migrating larvae
which have
penetrated the
diaphragm and
pleura in the first
stage
39
40. Lateral chest
radiograph of a 38-
year-old Korean
man with
paragonimiasis
shows a worm
migration tract
identified by the
meandering linear
opacity (arrow)
abutting the major
pleural fissure
40
41. Ring-shaped opacities of contiguous cavities giving the
characteristic appearance of a bunch of grapes are
highly suggestive of pulmonary paragonimiasis.
41
42. CT and MRI of the brain
Central nervous system disease may provide similar
"grapebunch“ findings, characteristically seen in the
temporal and occipital lobes on computed tomography
of the brain
42
44. MRI of cerebral
paragonimiasis in its
early active stage in a 24-
year-old Korean woman.
Contrast-enhanced TI-
weighted images show
multiple conglomerate,
ring-enhancing lesions
with massive
surrounding edema in
the right frontal lobe.
Note the mass effect
distorting and
displacing the frontal
horn and body of the
right lateral ventricl
44
45. Management:
Praziquantel is the drug of choice:
adult or pediatric dosage, 25 mg/kg given orally 3
times per day for 2 consecutive days.
Alternatives:
Triclabendazole (not available in the U.S.), adult or
pediatric dosage, 10 mg/kg orally once or twice;
or Bithionol: adult or pediatric dosage, 30-50 mg/kg
on alternate days for 10-15 doses.
45
46. For cerebral disease, Treat cautiously
a short course of corticosteroids may be given.
dexamethasone 4 mg IV q6 h as cover
neurological deterioration, in some cases producing
seizures and coma. Beware of raised ICP due to dying
parasites.
46
47. Prevention
improve health education to decrease consumption of
undercooked crustaceans
mass treatment of persons in endemic areas.
Never eat raw freshwater crabs or crayfish.
Cook crabs and crayfish for to at least 145°F (~63°C).
Travelers should be advised to avoid traditional meals
containing undercooked freshwater crustaceans.
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