Paragonimiasis is a disease caused by species of lung flukes of the genus Paragonimus. Eight species have been identified which use man as a host, and the disease has a range of Asia, Africa, and the Americas. The most predominant infective species are P. westermani and P. kellicotti.
P. westermani
map from:
P. kellicotti

North America

  • USA: Missippi Basin, Atlantic Coast, Midwest
  • Canada: Ontario, Quebec
1) Blair, et al.
History of Discovery

The earliest reported observation of Paragonimus was in an otter, Lutra braziliense, in Brazil during 1850. Subsequently, forty more species would be described all over the world in a breadth of hosts from mammals to crustaceans. P. westermani became known to the western scientific community in1878, when seen in a Bengal tiger of an Amsterdam zoo. The species name is derived from that of the zookeeper, a Mr. Westerman. P. kellicotti was described in 1908.

2)Yokogawa, M & 3) Desowitz, R

P. westermani


The adult fluke is often described as a coffee bean in size and appearance. It is hermaphroditic, with two testes and one ovary. The trematode has two suckers for attachment, an oral cavity, and a genital pore. Most of the body is occupied by the reproductive organs, the largest being the uterus. The exterior of P. westermani is covered with a spiny cuticle.


The eggs of P. westermani are 80 to 120 micrometers in length and have their greatest width near the equator.


Metacercariae are usually encysted in tissue. The exterior is spined and has two suckers.



Cercaria (not shown):

Cercariae are often indistinguishable between species. There is a large posterior sucker, and the exterior is spined.

1) Blair et al. & 4) Markell et al.
Life Cycle of P. westermani
Diagram from:
Clinical Presentation

General Symptoms:

Following consumption of P. westermani, the larvae pass through intestines and into the lungs, causing the first symptoms of pneumothorax, pleural effusion, and eosinophilia. Later, once the worms are reproducing in the lung tissue, pulmonary infiltrates and hemoptysis occur, the sputum containing dark brown eggs. Without therapy, chronic infection could bring about pulmonary fibrosis, bronchiectasis, and persistent pleural effusion.

5) Pachucki et al.

Case Studies in Literature:

  • Pachucki, CT, Levandowski, RA, Brown, VA, Sonnenkalb, BH, Vruno, MJ. American paragonimiasis treated with Praziquantel. New Eng J Med 1984; 311:582-3
  • Heath, HW, Marshal, HG. Pleural paragonimiasis in a Loation child. Ped Infec Dis J 1997; 16:1182-1185
  • Procop, GW, Marty, AM, Scheck, DN, Mease, DR, Maw, GM. North American Paragonimiasis: A case report. Acta Cytol 2000; 44: 75-80.


Encapsulated cyst in lung
Cross section of lung from patient infected with P. westermani

Transmission of the parasite P. westermani to humans and mammals primarily occurs through the consumption of raw or undercooked seafood. Accidental transfer of infective cysts can occur via food preparers who handle raw seafood and and subsequently contaminate cooking utensils and other foods (2). Consumption of animals which feed on crustaceans can also transmit the parasite, for cases have been sited in Asia where raw boar meat was the source of human infection (6).

In Asia, an estimated 80% of freshwater crabs carry P. westermani (5). In Japan and Korea, the crab specie Eriocheir is an important item of food as well as a notable second intermediate host of the parasite (2). Food preparation techniques such as pickling and salting do not kill the infective organism. In China, the practice of eating "drunken crabs" is especially risky: in an experiment in which crabs were immersed in wine (47% alcohol) for 3-5 minutes, then after five days fed to cats and dogs, the infection rate was 100% (2).

Diagnostic Tests
Definitive diagnosis can only be made in the lab, with the identification of eggs in sputum or stool. There must also have been a history of exposure, such as travel to endemic areas, or the consumption of undercooked seafood. Sero assays such as ELISA are also highly effective for diagnosis.
Therapy & Prevention

An effective drug for the treatment of trematode or cestode infection is praziquantel. There is no noted instance of resistance to this drug (7). The standard dosage of 75 mg/kg per day, divided into 3 doses over 2 days has proven to eliminate P. westermani and P. kellicotti infections in man (5). Because of the broad-spectrum effects of praziquantel, it may be suitable for mass treatment programs in endemic areas such as Africa, Central and South America, and Asia (7). Another drug biothionol has also proven effective and yields few side effects (2).

Prevention programs could target habits of food preparation, promoting safer cooking techniques and more sanitary handling of potentially contaminated seafood.

The elimination of the first intermediate host, the snail, via spraying programs is not tenable due to the nature of the organisms habits (2).


  1. Blair, D, Xu, Z-B, Agatsuma, T. Paragonimiasis and the genus Paragonimus. Adv Parasitol 1998; 42: 113-222.
  2. Yokogawa, M. Paragonimus and Paragonimiasis. Adv Parasitol 1965; 3: 99-158
  3. Desowitz, R. New Guinea Tapeworms and Jewish Grandmothers: Tales of Parasites and People. New York: WW Norton, 1987.
  4. Markell, EK, John, DT, Krotoski, WA. Medical Parasitology. Philadelphia: WB Saunders Co, 1999.
  5. Pachucki, CT, Levandowski, RA, Brown, VA, Sonnenkalb, BH, Vruno, MJ. American Paragonimiasis treated with praziquantel. New Eng J Med 1984; 311: 582-583.
  6. Miyazaki, I, Habe, S. Newly recognized mode of human infection with the lung fluke Pargonimus westermani. J Parasitol 1976; 62: 646-648.
  7. Croft, S. The current status of antiparasite chemotherapy. Parasitol 1997; 114: 3-15.
  8. Procop, GW, Marty, AM, Scheck, DN, Mease, DR, Maw, GM. North American Paragonimiasis: A case report. Acta Cytol 2000; 44: 75-80.

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Christina I. Baumann, May 2001