Paragonimus spp

From Dog
Egg of P. harinasutai collected in feces from a dog[1]
Adult P. harinasutai recovered from a dog. O: ovary; OS: oral sucker; T: testis; U: uterus; VS: ventral sucker[1]

Paragonimus spp are a zoonotic parasitic hermaphroditic, digenetic trematode lung fluke of dogs in Asia and the Americas.

Human cases of paragonimiasis have been reported mostly from Japan, Korea, Formosa, China, Manchuria, the Philippine Islands, India, parts of tropical West Africa and Latin America. An estimated 22 million people are infected worldwide with paragonimiasis[2].

Species which are pathogenic to dogs include:

  • Paragonimus kellicotti (USA)
  • Paragonimus westermani (Asia)[3]
  • Paragonimus skrjabini skrjabini[4]
  • Paragonimus skrjabini miyazakii
  • Paragonimus westermani
  • Paragonimus cenocopiosus (syn Euparagonimus cenocopiosus)
  • Paragonimus harinasutai
  • Paragonimus bangkokensis[5]
  • Paragonimus heterotremus[6]
  • Paragonimus hueit'ungensis[7]

The life cycle of this parasite involves two intermediate hosts, an aquatic snail and crustaceans (e.g. crabs, crayfish). Dogs and humans ingest metacercariae in infected undercooked crustaceans or other definitive hosts (e.g. pigs)[8]. Within the dog, metacercariae excyst into the small intestine; the juvenile flukes develop and penetrate the intestinal wall into the peritoneal cavity. They then migrate into the abdominal wall or liver, where they undergo further development. Approximately one week later, the adult flukes reenter from the abdominal cavity and penetrate the diaphragm to reach the pleural space and lungs[9]. Ectopic locations can result due to aberrant migrations, including the brain and skin. Within the dog lungs, adult flukes form cysts which have numerous interconnected tubular channels within their own walls and these channels have connections with the cavity and the adjacent distal bronchus.

In North America, P. kellicotti causes infections among dogs, cats, and wild carnivores, but rarely infects humans[10].

Clinical signs in dogs begin to develop 5 - 6 months post-infection and include fever, cough, pleural effusion, pneumothorax and eosinophilia.

Ectopic infections have been reported in dogs, with inguinal nodules forming as a result, leading to lymphadenopathy, lymphadenitis and cellulitis[11].

Diagnosis is by coprological examination[12], radiographic evidence of nodules within the lung parenchyma[13], seropositivity on ELISA[14] and postmortem evidence of adult parasites in the lungs.

A differential diagnosis would include other lung parasites such as Dirofilaria spp, Strongyloides spp, Filaroides osleri, Angiostrongylus vasorum, Eucoleus aerophilus, Crenosoma vulpis and Aelurostrongylus abstrusus.

Treatment with praziquantel at 23 mg/kg three time daily for 3 days has been shown to be effective at eliminating P. kellicotti from the lungs of dogs[15]. Fenbendazole is also effective at 50 mg/kg for 10 - 14 days.

Triclabendazole has a proven efficacy against P. westermani when given at 100 mg/kg daily for 2 consecutive days[16].


  1. 1.0 1.1 Sohn WM et al (2009) Indochinamon ou (Crustacea: Potamidae) as a new second intermediate host for Paragonimus harinasutai in Luang Prabang Province, Lao PDR. Korean J Parasitol 47(1):25-29
  2. Lee CH et al (2007) Serial CT findings of Paragonimus infested dogs and the Micro-CT findings of the worm cysts. Korean J Radiol 8(5):372-381
  3. Xiao SH et al (2010) Effectiveness of mefloquine against Clonorchis sinensis in rats and Paragonimus westermani in dogs. Parasitol Res 107(6):1391-1397
  4. Singh ST et al (2006) Possible discovery of Chinese lung fluke, Paragonimus skrjabini in Manipur, India. Southeast Asian J Trop Med Public Health 37(3):53-56
  5. Odermatt P et al (2007) Paragonimiasis and its intermediate hosts in a transmission focus in Lao People's Democratic Republic. Acta Trop 103(2):108-115
  6. Le TH et al (2006) Paragonimus heterotremus Chen and Hsia (1964), in Vietnam: a molecular identification and relationships of isolates from different hosts and geographical origins. Acta Trop 98(1):25-33
  7. Singh TS (2002) Occurrence of the lung fluke Paragonimus hueit'ungensis in Manipur, India. Zhonghua Yi Xue Za Zhi (Taipei) 65(9):426-429
  8. Kirino Y et al (2009) A seroepidemiological survey for paragonimosis among boar-hunting dogs in central and southern Kyushu, Japan. Vet Parasitol 161(3-4):335-338
  9. Yokogawa M (1969) Paragonimus and paragonimiasis. Adv Parasitol 7:375–387
  10. Centers for Disease Control and Prevention (CDC) (2010) Human paragonimiasis after eating raw or undercooked crayfish - Missouri, July 2006-September 2010. MMWR Morb Mortal Wkly Rep 59(48):1573-1576
  11. Madarame H et al (2009) Ectopic (subcutaneous) Paragonimus miyazakii infection in a dog. Vet Pathol 46(5):945-948
  12. Cheng YZ et al (2010) Survey on the foci of Paragonimus in Youxi, Yongtai and Pinghe Counties of Fujian Province. Zhongguo Ji Sheng Chong Xue Yu Ji Sheng Chong Bing Za Zhi 28(6):406-410
  13. Palić J et al (2011) What is your diagnosis? Aspirate of a lung nodule in a dog. Paragonimiasis. Vet Clin Pathol 40(1):99-100
  14. Nakano N et al (2009) Large-group infection of boar-hunting dogs with Paragonimus westermani in Miyazaki Prefecture, Japan, with special reference to a case of sudden death due to bilateral pneumothorax. J Vet Med Sci 71(5):657-660
  15. Bowman, DD (2009) Georgis' parasitology for veterinarians. 9th edn. Elsevier Saunders, Missouri. pp:125
  16. Liu Y et al (1999) Experimental observation of effects of triclabendazole on Paragonimus westermani infection in dogs. Chin Med J (Engl) 112(4):345-348