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( 卫氏并殖 吸虫）, Pagumogonimus skrjabini( 斯氏狸殖吸虫 ).

Paragonimus westermani This worm was first found in a tiger ’ s lung in India in 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 ×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.

A adult of Paragonimus westermani

A adult of P. westermani

2. Egg is irregularly elliptic, golden yellow in color, ×48-60 µ 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 µ with two layers of transparent walls, in crab and crayfish.

. The oval ova have an operculum and are by µ m. It is golden yellow in color. The shell is uneven in thickness. The content is an ovum and more than 10 yolk cells.

Egg of P. westermani

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: 1 st int. host is melania snail( 川 卷螺 ). 2 nd 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

penetrate the diaphragm adolescents adults in lungs eggs Migrate to the lungs excystation In Human Body duodenum Discharged in sputum man eats raw crab or or in feces crayfish with metacercaria ──────────────────────────── Metacercariae Eggs get into water invade crab In Water ℃ and crayfish 3-4weeks Miracidia hatch out invades Cercariae Melania snail Escape asexual reproduction Cercariae Daughter rediae Mother rediae Sporocysts

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( 夏科 - 雷登氏晶体）, 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.

2. Clinical manifestation: Paragonimiasis may be classified into 4 types : (1)Pulmonary type: the symptoms resemble pulmonary tuberculosis( 结核 )with low fever, loss of appetite, night sweating, chest pain, loss of weight and rusty sputum. (2) Brain type: manifests epilepsy( 癫痫 ), hemiplegia( 偏瘫 ), monoplegia( 单瘫 ),aphasia( 失语 ), visual disturbence and resembles cerebral cystcercosis( 脑囊虫病 ). (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.