Paragonimus
Paragonimus
These worms’ reproductive organs
stand side by side. Adult worms usually
live in the lungs of man and carnivores
causing paragonimiasis, so they are
also called lung flukes. It is essentially a
zoonosis.
species
In
of
china,
lung
there
flukes
of
are
two
medical
importance: Paragonimus westermani,
Pagumogonimus skrjabini
Paragonimus westermani
This worm was first found in a tiger’s
lung in India in 1877. It is the main kind of
lung flukes infecting man. In our country it
is prevalent in 22 provinces, city and
autonomic region except Xinjiang, Xizang,
Qinghai, Gansu, Ningxia, Inner Mongolia
and Shandong.
I. morphology
1. Adult: The body is elliptic, dorsally it is convex, ventrally it
is flattened, reddish-brown in color, about 7.5-12×4-6×1-3
mm (length:width=2:1). It looks like half a peanut. The sizes of
two suckers are sub-equal. The ventral sucker is located in the
central position of the body. Two testes, the ovary and the
uterus are situated side by side. The vitellaria is well
developed. The excretory bladder extends forward to the level
of pharynx. The digestive tract is divided into two ceca.
2. Egg is irregularly elliptic, golden yellow in
color, 80-110×48-60µ in size. The thick
and
asymmetric
shell
with
a
distinct
operculum encloses an ovum surrounded
by more than 10 yolk cells.
3. Metacercaria is spherical, about 300400µ with two layers of transparent walls,
in crab and crayfish.
 The oval ova have
an operculum and
are 80-110 by 4880 µm. It is golden
yellow in color. The
shell is uneven in
thickness.
The
content is an ovum
and more than 10
yolk cells.
II. Life cycle
1. Infective stage: metacercaria
2. Infective mode: eating raw fresh water crabs
and crayfish with metacercariae
3. Infective route: by mouth
4. Site of inhabitation: lungs
5. Intermediate hosts: 1st int. host is melania
snail. 2nd int. hosts are crab and crayfish.
6. Reservoir hosts: carnivores such as tiger,
lion, wolf, fox, dog, leopard, cat and etc
7. Life span: 5-6 years
III. Pathology and Symptomatology
Adults
inhabit
lungs,
although
other
organs are also involved.
1. Pathological lesions may be classified
into 4 stages: (1)Invading and migrating
stage:
After
excystation
the
adolescents
penetrate the intestinal wall and migrate to the
lungs. (2) Suppurative stage. The bleeding
and infiltration of neutrophils and eosinophils
surrounding worms form a capsule, abscess.
(3) Cystic stage, the cyst wall is formed due to the
progressive fibrosis of the surrounding tissue. The
cystic contents are chocolate or rusty thick fluid
with eggs and Charcot-Leyden crystals, which
looks like sesame paste. The shadow of the cyst
can be seen on X-ray. Patients cough out the rusty
sputum when the cyst communicates with the
bronchioles. (4) Fibrous-scar stage, the worms are
dead or escape from the cyst. The exudate and pus
are expelled or absorbed and replaced by fibrousscar tissue.
2. Clinical manifestation:
Paragonimiasis may be classified into 4 types :
(1)Pulmonary type: the symptoms resemble pulmonary
tuberculosiswith low fever, loss of appetite, night sweating,
chest pain, loss of weight and rusty sputum.
(2)
Brain
type:
manifests
epilepsy,
hemiplegia,
monoplegia,aphasia, visual disturbence and resembles
cerebral cystcercosis
(3)Abdominal type: abdominal pain ， diarrhea or
dysentery with blood, mucus and ova in feces.
(4)Subcutaneous type: the wandering and painless
subcutaneous nodules.
IV. Diagnosis
1. Sputum examination: (1) Alkali
digestive method (10%NaOH), (2) Direct
sputum smear
2. Stool examination: (1) Alkali digestion ,
(2) Water sedimentation method, (3)
Direct fecal smear
3. Biopsy for Subcutaneous type
4. CT for brain type
5. Immunological tests for reference.
V. Treatment and Prevention
1.Treatment: Drug of choice is praziqantel.
Other
effective
drugs
include
hexachloroparaxylol, bithionol (bitin).
2. Prevention:
(1) Health education,
(2) Avoid eating raw fresh water crabs and
crayfishes.
(3) Avoid sputum and stool getting into water.
VI. Epidemiology
This disease is prevalent in Far East,
Africa and South America. There are
endemic
foci
in 22
provinces
in
Northeast, East and Southwest of
China. Its prevalence is related to
eating raw crabs and crayfishes and
the natural foci.