Paragonimus kellicotti

Geographic Range

Paragonimus kellicotti was first discovered in Kentucky. Due to its geographic range, this lung fluke is more commonly known as the North American lung fluke. However, over the years, this fluke has become widespread and even cases of infected dogs with P. kellicotti have been studied in the Middle East, particularly in Israel. (Harley, November 1971; Harrus, 1997)


As internal parasites with complex life cycles, this species is found where its hosts dwell. The larval stages parasitize snails and then crustaceans, mainly crawfish and crabs, and therefore dwell in fresh or saltwater. Adult North American lung flukes parasitize cats, dogs, minks, muskrats, and humans. At this stage, they occupy a wide range of terrestrial habitats. (Procop, Jan. - Feb. 2000; Wallace, May 1, 1931)

  • Aquatic Biomes
  • temporary pools
  • coastal

Physical Description

Adult lung flukes are dorso-ventrally flattened, soft-bodied parasites. The tegument is covered with spines. These parasites are usually brown in color and oval in shape, resembling a coffee bean. Oral and ventral suckers are almost equal in size. Ventral suckers allow them to attach to the host. Paragonimus species are usually distinguished from one another by the metacercaria and tegumental spine shape. (Burt, 1970; Roberts and Janovy, Jr., 2000; Schell, 1985)

  • Range length
    8 to 16 mm
    0.31 to 0.63 in


The adult fluke infects cats, dogs, mink, or muskrats. The adult fluke passes its eggs in soil or feces, and the eggs hatch and develp into a miricidium. The miricidium penetrates its first intermediate host, usually a gastropod, Pomatiopsis lapidaria. From the miricidium, several asexually active sporocysts forms and then redia, another larval form. Cells within the redia produce cercariae, a free living stage. Cercariae leave the snail and infects the second intermediate host, a crawfish or crab. The cercariae encyst in tissue and are then termed metacercariae. When an animal or human eats these crustaceans they swallow these infected hosts, and the cysts are broken down by the digestive enzymes. The juvenile parasites become the adult form and lays its eggs again. The new larvae begin to feed on the intestine of the human, and the cycle begins again. (Brusca and Brusca, 2003; Schell, 1985)


As adults, this species of lung flukes parasitizes vertebrate hosts, usually a mink, muskrat, dog, or a cat. They are hemaphroditic, including both female and male sex organs, so they can self-fertilize. The eggs of the flatworm are usually swallowed by the animal through food or water and collected in the trachea which then passes to the pharynx. The animal releases the eggs through its feces, where the eggs develop and hatch in a period of about 3 weeks. (Burt, 1970; Schell, 1985)

There is no parental investment for this parasite.

  • Parental Investment
  • no parental involvement


This specific lung fluke, P. kellicotti, has been known to survive for a period of up to 20 years in the lungs of a living human body. Lung flukes live so long because they go through several hosts - as many as three different hosts. (Burt, 1970; Schell, 1985)


The North American lung fluke can function on its own, but mostly live in groups in their hosts. (Meglitsch and Schram, 1991)

Communication and Perception

Bristles and small spines probably act as tactile receptors, and these animals also may have reduced chemoreceptors. These flukes use their ventral suckers as a means of identifying their surroundings. These suckers are used to feel around their host and feel any other adult flukes that might be present. These parasites also have nerve endings that allow them to feel other flukes as they pass by. (Brusca and Brusca, 2003; Meglitsch and Schram, 1991; Schell, 1985)

Food Habits

North American lung flukes absorb body fluids from the tissues of their hosts. For example, the lungs of cats, dogs, mink, or muskrats. (Harrus, 1997; Wallace, May 1, 1931)

  • Animal Foods
  • body fluids


These animals are probably not preyed on directly but are ingested. Egg and larval mortality are high since the parasites often do not reach appropriate hosts.

Ecosystem Roles

This species is parasitic, infecting minks, muskrats, pigs, cats, and dogs. After being infected, these animals will eventually die if they are not treated. (Harley, November 1971)

Species Used as Host

Economic Importance for Humans: Positive

The only positive influence P. kellicotti has is the contribution given to scientific research. Like all flukes, this species of fluke is a parasite and can provide information about the development and living conditions of the species. Scientific research of the lung fluke can provide physicians with answers to the causes of various human diseases and can allow scientists to determine the ecological effects for various countries. (Harrus, 1997; Procop, Jan. - Feb. 2000)

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

As an adult, this flukeworm lives in the lungs of humans and other mammals. Over time it reproduces in the lung and the lining of the wall slowly deteriorates. Patients can be treated with antibiotics or surgery. However, in severe cases of infection, the patient will die if surgery is not performed. Even with surgery, it is not guaranteed that all the larvae have been removed. Not only does this affect the patient, but it also affects the economy. It takes money from the patient as well as the hospital to perform such risky procedures, especially those surgeries dealing with a vital organ of life. (Procop, Jan. - Feb. 2000)

Conservation Status

P. kellicotti is not in need of conservation.

Other Comments

North American lung flukea have been studied for over 200 years. Research is still being done to see how humans can be saved when infected by these flukes. Surgery may reduce the risk of death in severe cases, but removal of all the larvae is not certain. (Procop, Jan. - Feb. 2000)


Luisa Arellano (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.



living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map


living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map


living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal


Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.


uses smells or other chemicals to communicate


the nearshore aquatic habitats near a coast, or shoreline.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature


union of egg and spermatozoan


forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.


mainly lives in water that is not salty.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body


referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.


marshes are wetland areas often dominated by grasses and reeds.


having the capacity to move from one place to another.


This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death


rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

scrub forest

scrub forests develop in areas that experience dry seasons.


remains in the same area


reproduction that includes combining the genetic contribution of two individuals, a male and a female


living in residential areas on the outskirts of large cities or towns.


a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.


A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.


living in cities and large towns, landscapes dominated by human structures and activity.

year-round breeding

breeding takes place throughout the year


Brusca, R., G. Brusca. 2003. Invertebrates. Sunderland, Massachusetts: Sinauer Associates, Inc..

Burt, D. 1970. Platyhelminthes and Parasitism: An Introduction to Parasitology. New York: American Elsevier Publishing Co., Inc.

Harley, J. November 1971. Paragonimus kellicotti in Kentucky. American Midland Naturalist, 88 (2): 474-475.

Harrus, S. 1997. Sudden death due to Paragonimus kellicotti infection in a dog. Veterinary-Parasitology, 71 (1): 59-63.

Meglitsch, P., F. Schram. 1991. Invertebrate Zoology Third Edition. New York: Oxford University Press.

Nolan, T. 2004. "Paragonimus kellicotti Homepage" (On-line). Diagnosis of Veterinary Endoparasitic Infections. Accessed November 07, 2004 at

Procop, G. Jan. - Feb. 2000. North American paragonimiasis: A case report. Acta-Cytologica, 44 (1): 75-80.

Roberts, L., J. Janovy, Jr.. 2000. Foundations of Parasitology. Boston: McGraw Hill.

Schell, S. 1985. Trematodes of North America. Idaho: University Press of Idaho.

Wallace, F. May 1, 1931. The North American Lung Fluke. Science, New Series, 73 (1896): 481-482.