Paragonimus westermani - Introduction, Classification, History, Habitat, Morphology, Epidemiology, Reservoir, Transmission

Introduction to Paragonimus westermani

Paragonimus westermani is the etiological agent of pulmonary paragonimiasis or hemoptysis in humans. It is a lung fluke which is most common in eastern Asia and in South America.

Classification of Paragonimus westermani

Kingdom: Animalia

Phylum: Platyhelminthes

Class: Trematoda

Order: Plagiorchiida

Family: Paragonimidae

Genus: Paragonimus

Species: P. westermani

History of Paragonimus westermani

Coenraad Kerbert discovered Paragonimus westermani in 1878 in Bengal tigers kept in Amsterdam zoo. In 1879, the fluke was found during an autopsy of a Portuguese man while it was demonstrated by Manson in the sputum of a Chinese patient in 1880.

The life cycle of the parasite was eventually described by Yokogawa and Kobayashi between 1917 to 1921.

Habitat of Paragonimus westermani

In definitive hosts such as a human, adult Paragonimus westermani habitat in the parenchyma of the lung close to the bronchioles.

Morphology of Paragonimus westermani

The important morphological features of Paragonimus westermani include adult worms, eggs, and the infective form metacercaria.

Adult form

• the adult form of Paragonimus westermani is thick and fleshy

• egg-shaped fluke is reddish brown when freshly passed out

• measures 7.5mm to 12mm in length, 4mm to 6mm in breadth, and 3.5 to 5mm in thickness

• the anterior end is slightly broader than the posterior end

• two muscular suckers – oral sucker and ventral sucker

  * oral sucker is present in the anterior end

  * ventral sucker is present on the ventral surface near the middle part of the body

• the large excretory bladder which extends from the posterior extremity to the level of the pharynx

• irregular deeply lobed testes are present side by side in the posterior end a characteristic feature of Paragonimus westermani

• absence of cirrus sac

• adult fluke has a lifespan of 6 to 7 years

Egg

• Paragonimus westermani eggs are oval in shape, golden-brown in color

• measures 48μm to 60μm by 80μm to 118μm

• operculated eggs with clearly visible operculum at the large side and the opposite end without operculum are thick

• unembryonated eggs are excreted in stool or sputum

Infective form

The infective form of Paragonimus westermani is the metacercaria.

Metacercaria

• infective to definitive host including man

• encysted form is found in the flesh of crustaceans such as freshwater crayfish, crabs

Epidemiology of Paragonimus westermani

Epidemiology studies of Paragonimus westermani have confirmed infections in China, Japan, Korea, Taiwan, Laos, Thailand, Russian provinces, Peru, Ecuador, Philippines, India, etc.

Other species of Paragonimus have been reported in the Americas and Africa.

Reservoir, Source of Paragonimus westermani

The second intermediate host includes several genera of crab fish including Potamon, Sinopotamon, Parathelhusa and freshwater crayfish harboring metacercaria are the source of Paragonimus westermani infection.

The reservoir of Paragonimus westermani is the man, domestic animals, and wild carnivores. Body secretions such as sputum and stool containing Paragonimus westermani eggs contaminate water bodies such as lakes, pools, and rivers which infects the intermediate hosts freshwater snails belonging to the family Pleuroceridae, Thiaridae – Genera: Semisulcospira, Brotia while Semisulcospira libertina is the optimal intermediate host.

Transmission of Paragonimus westermani

Transmission of Paragonimus westermani occurs via the following routes:

• consumption of raw, undercooked crab, and crayfish (also includes delicacy as soaked in wine or drinking raw crabs or crayfish)

• less common – consumption of pork, wild pigs containing Paragonimus westermani larvae

• via contaminated hands, utensils, and clothes used for staining