Lung fluke
| Paragonimus | |
|---|---|
 |
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| Egg of Paragonimus westermani | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Platyhelminthes |
| Class: | Trematoda |
| Order: | Plagiorchiida |
| Family: | Troglotrematidae |
| Genus: |
Paragonimus Braun, 1899 |
Paragonimus is a genus of flatworms (platyhelminths). Some tens of species have been described, but they are difficult to distinguish, so it is not clear how many of the named species may be synonyms. Several of the species are known as lung flukes. In humans some of the species occur as zoonoses; the term for the condition is paragonimiasis. The first intermediate hosts of Paragonimus include at least 54 species of freshwater snails from superfamilies Cerithioidea and Rissooidea.
The most prominent species of Paragonimus in human medicine is Paragonimus westermani, an infectious lung fluke originating in eastern Asia. Worldwide, about nine species of Paragonimus are known to cause human paragonimiasis in which many of the species reside in East Asia, West Africa, and in North and South America.
Species of Paragonimus vary in size; the adult stage might attain a length of up to 15 millimetres (0.59 in) and a width of up to 8 mm (0.31 in). The adult flatworm has an oval shape body with spines covering its thick tegument. Both the oral sucker and acetabulum are round and muscular. The acetabulum is slightly bigger than the oral sucker – 0.19 mm and 0.12 mm, respectively.Ovaries are located behind the acetabulum and posterior to the ovary are the testes. The seminal receptacle, the uterus and its metraterm, the thick-walled terminal part, lie between the acetabulum and the ovary.
The parasite passes through two intermediate hosts, an aquatic snail and a crustacean. It enters its mammalian definitive hosts when they eat infected freshwater crustaceans. Typical hosts include dogs, cats, and humans. Humans usually contract paragonimiasis when they eat undercooked freshwater crabs or crayfish, that contain live metacercariae. In the intestine, the parasite will move into the abdomen and commonly into the lungs. In the lung, the parasites encyst and cross fertilize each other. The cyst eventually ruptures in the lungs and the eggs may be coughed up or swallowed and excreted in the feces. An egg landing in fresh water hatches and releases a ciliated miracidium. A successful miracidium swims about until it finds an intermediate host, usually an aquatic snail. A crustacean in turn becomes infected by eating infected snails. The definitive host completes the cycle if it eats infected crustaceans.
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Wikipedia