Paragonimiasis

Paragonimiasis
Classification and external resources
Specialty	infectious disease
ICD-10	B66.4
DiseasesDB	30756
eMedicine	ped/1729
Patient UK	Paragonimiasis
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Paragonimiasis is a food-borne parasitic infection caused by the lung fluke, most commonly Paragonimus westermani. It infects an estimated 22 million people yearly worldwide. It is particularly common in East Asia. More than 30 species of trematodes (flukes) of the genus Paragonimus have been reported; among the more than 10 species reported to infect humans, and only 8 bringing about infections in humans, the most common is P. westermani, the oriental lung fluke.

The U.S. Centers for Disease Control and Prevention (CDC) has a detailed description and an explanatory image of the Paragonimus lifecycle: [1]

The first human case was seen in 1879 in Taiwan. An autopsy was done and adult trematodes were found in the lungs. The adult flukes have a reddish-brown in color with an ovoid like shape. They have 2 muscular suckers, the first an oral sucker located anteriorly and the second a ventral sucker located mid-body. The adult flukes can live up to 20 years. The eggs are golden brown in color and are asymmetrically ovoid. They have a very thick shell. As seen above, these trematodes have a very complex life cycle with 7 distinct phases involving 2 intermediate hosts and humans. These 7 phases phases are outlined as follows: eggs reach fresh water where they develop into miracidia. These penetrate many species of aquatic snails (first intermediate host) where they go through 3 distinct stages. The first being sporocysts, the second being rediae, and the third being cercariae, also referred to as the larvae. These larvae released into water and penetrate crabs, crayfish and other crustaceans (second intermediate host). The cercariae situate themselves into the gills, liver and muscles where they further develop into metacercariae. When the parasite-filled crustacean is eaten, the metacercariae hatch in the intestine. These young worms penetrate intestinal wall, peritoneum, the diaphragm and the pleura where they finally reach the lungs. Here they live in pairs, lay eggs that are coughed up in sputum to restart the cycle.

There are more than 30 known species of Paragonimus. Species of Paragonimus are widely distributed in Asia, Africa, and North and South America. Paragonimus westermani is found in southeast Asia and Japan, while Paragonimus kellicotti is endemic to North America.Paragonimus africanus is found in Africa and Paragonimus mexicanus is found in central and South America. Just as the species imply, paragonimiasis is more prominent in Asians, Africans and Hispanics because of their region and cultures. Prominence increases with age from older children to young adults then decreases with age.It is also higher among the female populations. This is a very common parasite of crustacean eating mammals.

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Wikipedia