paragonimiasis

Introduction Lung fluke : A kind of chronic disease Adult worms usually live in the lungs of man and carnivores causing paragonimiasis Intermediate hosts: 1st int. host is melania snail. 2nd int. hosts are crab and crayfish. It is essentially a zoonosis. Also called Japanese lung fluke or oriental lung fluke cause a sub-acute to chronic inflammatory disease of the lung. reservoir hosts including dogs, cats

Morphology 1. Adult: The body is elliptic, dorsally it is convex, ventrally it is flattened, reddish-brown in color Adult worms are 7.5 mm to 12 mm long and 4 mm to 6 mm wide. The thickness ranges from 3.5 mm to 5 mm. The skin of the worm (tegument) is thickly covered with scale like spines The oral and ventral suckers are similar in size The ventral sucker is located in the central position of the body.

Two testes, the ovary and the uterus are situated side by side 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 EGG: range from 80 to 120 µm long by 45 to 70 µm wide. They are yellow-brown, ovoid or elongate, with a thick shell , operculate , ovum surrounded by more than 10 yolk cells.

metacercaria

Life cycle Unembryonated eggs are passed in the sputum of a human or feline. Two weeks later, miracidia develop in the egg and hatches. The miracidia penetrate its first intermediate host (snail). Within the snail mother sporocyst form and produce many mother rediae, which subsequently produce many daughter rediae which shed crawling cercariae into fresh water. The crawling cercariae penetrate fresh water crabs and encyst in its muscles becoming metacercaria. Humans or felines then eat the infected crabs raw. Once eaten, the metacercaria excysts and penetrates the gut, diaphragm and lung where it becomes an adult worm

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, 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.

Clinical manifestation (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.

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. 6-History of eating raw crustaceans (crabs or crayfish-

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