Thursday, February 18

Paragonimus Westermani

Hospes And Disease Name

Humans and animals that eat the crab / shrimp. Like Cats' dog 'tiger' wolf ' pigs and a variety of feline species can also harbor P. westermani . Is the host of this worm.
In humans this parasite causes paragonimiasis.
Paragonimiasis is a food-borne parasitic infection caused by the lung fluke which can cause a sub-acute to chronic inflammatory disease of the lung. It’s one of the more recognized lung flukes with the widest geographical range.

Geographic Endemic

This worm is found in the Republic of China, Taiwan, Japan, philippines, vietnam, thailand, india, malaysia, Africa , South and Central America .

Morphology and Life Cycle

Size, shape, and color resemble a coffee bean when alive. 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 heavily covered with scalelike spines. The oral and ventral suckers are similar in size, with the later placed slightly pre-equatorially. The excretory bladder extends from the posterior end to the pharynx. The lobed testes are adjacent from each other located at the posterior end, and the lobed ovaries are off-centered near the center of the worm (slightly postacetabular). The uterus is located in a tight coil to the right of the acetabulum, which is connected, to the vas deferens. The vitelline glands, which produce the yolk for the eggs, are widespread in the lateral field from the pharynx to the posterior end. By viewing the tegumental spines and shape of the metacercariae, one could distinguish between the ~30 species of Paragonumus spp.

* Eggs: Paragonimus westermani eggs range from 80 to 120 µm long by 45 to 70 µm wide. They are yellow-brown, ovoid or elongate, with a thick shell, and often asymmetrical with one end slightly flattened. At the large end, the operculum is clearly visible. The opposite (abopercular) end is thickened. The eggs are unembryonated when passed in sputum or feces (CDC).
* Cercaria (not shown): Cercariae are often indistinguishable between species. There is a large posterior sucker, and the exterior is spined.
* Metacercaria: Metacercariae are usually encysted in tissue. The exterior is spined and has two suckers
* Adults: Adult flukes are typically reddish brown and ovoid, measuring 7 to 16 mm by 4 to 8 mm, similar in size and appearance to a coffee bean.They are hermaphroditic, with a lobed ovary located anterior to two branching testes. Like all members of the Trematoda, they possess oral and ventral suckers.

In tissue: Hemorrhagic holes in the visceral pleura (white arrows) and adult worms acquired from the holes (black arrows). Bump of the visceral pleura is the subpleural worm cyst (red arrow)

Unembryonated eggs are passed in the sputum of a human or feline. Two weeks later, miracidum develop in the egg and hatches. The miracidum 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 metacerciaria excysts and penetrates the gut, diaphragm and lung where it becomes an adult worm in pairs.

Paragonimus has a quite complex life-cycle that involves two intermediate hosts as well as humans. Eggs first develop in water after being expelled by coughing (unembryonated) or being passed in human feces. In the external environment, the eggs become embryonated. In the next stage, the parasite miracidia hatch and invades the first intermediate host such as a species of freshwater snail. Miracida penetrate its soft tissues and go through several developmental stages inside the snail but mature into cercariae in 3 to 5 months. Cercariae next invade the second intermediate host such as crabs or crayfish and encyst to develop into metacercariae within 2 months. Infection of humans or other mammals (definitive hosts) occurs via consumption of raw or undercooked crustaceans. Human infection with P. westermani occurs by eating inadequately cooked or pickled crab or crayfish that harbor metacercariae of the parasite. 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. 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 (CDC).


The way to properly diagnose this parasite infection is by looking at the sputum and finding the eggs. Sometimes eggs are shed in the feces. Radiological methods can be used to X-ray the chest cavity and look for worms. This method is easily misdiagnosed, because pulmonary infections look like tuberculosis, pneumonia, or spirochaetosis. A lung biopsy can also be used to diagnose this parasite. An assay that detects worm antigens using monoclonal antibody can also be used for diagnosis.


praziquantel and Bithionol is a cure for this disease.

praziquantel* is the drug of choice to treat paragonimiasis. The recommended dosage of 75 mg/kg per day, divided into 3 doses over 2 days has proven to eliminate P. westermani . Bithionol is an alternative drug for treatment of this disease but is associated with skin rashes and urticaria. For additional information, see the recommendations in The Medical Letter (Drugs for Parasitic Infections).


You're really genius.Thanks 4 your info

Is That Microbe?? is Dangerously

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