Paragonimus

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Paragonimus
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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. In china,
  there are two species of lung flukes of medical
  importance Paragonimus westermani, Pagumogonimus
  skrjabini

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Paragonimus westermani

• This worm was first found in a tigers
  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.

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I. morphology

• 1. Adult The body is elliptic, dorsally
  it is convex, ventrally it is flattened,
  reddish-brown in color, about 7.5-124-61-3 mm
  (lengthwidth21). 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.

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• 2. Egg is irregularly elliptic, golden yellow in
  color, 80-11048-60µ 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 300-400µ with
  two layers of transparent walls, in crab and
  crayfish.

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• The oval ova have an operculum and are 80-110 by
  48-80 µm. It is golden yellow in color. The
  shell is uneven in thickness. The content is an
  ovum and more than 10 yolk cells.

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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

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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.

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• (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 fibrous-scar tissue.

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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.

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IV. Diagnosis

• 1. Sputum examination (1) Alkali digestive
  method (10NaOH), (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.

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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.

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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.