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Dracunculus insignis

By Daniel Fargo

Geographic Range

Dracunculus insignis is limited to North America. (Roberts and Janovy, Jr., 2000)

Habitat

While outside of a host, Dracunculus insignis is limited to aquatic environments. As such, D. insignis requires a semi-aquatic or fully aquatic host such as a mink, raccoon, otter, fisher, and occasionally domestic dogs. (Crichton and Beverly-Burton, 1975)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams
  • temporary pools

Physical Description

Dracunculus insignis adults are white cylindrical worms 17.6 to 23.0 cm in length and 3 to 4 mm at maximum width. Dracunculus insignis is dioecious. Females are much larger than males when they are filled with first-stage larvae. Larvae are approximately 500 microns long and 50 microns wide. Over the course of development, the head changes from a pointed shape to a dome shape by adulthood.

The worm's cuticle has three or more main outer layers made of collagen and other compounds. The outer layers are non-cellular and are secreted by the epidermis. The cuticle layer protects the nematodes so they can invade the digestive tracts of animals. The worms molt four times, the first two before hatching, and then before their adult stage.

Longitudinal muscles are along the body wall and are obliquely arranged in bands. Dorsal, ventral and longitudinal nerve cords are connected to the main body of the muscle.

The mouth leads to a thin esophagus and intestine. The male intestine is completely atrophied. As a nematode in the group Secernentea, these worms have a specialized tubular excretory system with three canals. The canals are arranged to form an “H”.The rectum is long and tubular in shape. (Barnes, 1987; Brusca and Brusca, 2003; Crichton and Beverly-Burton, 1975; Gibson and McKiel, 1972; Panciera and Stockham, 1988; Roberts and Janovy, Jr., 2000)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Range length
    17.6 to 23 mm
    0.69 to 0.91 in

Development

The life cycle of Dracunculus insignis is fairly simple and involves at least two hosts. Females carrying larvae internally release a toxin which causes the formation of a blister on the hosts skin. This blister bursts open on contact with water allowing the female to release her larvae upon contact with water. Dracunculus insignis passes through two larval stages in an intermediate copepod host, either Cyclops vernalis or C. bicuspidatus thomasi. After penetrating the intermediate host, larvae migrate to the hemocoel within one to two hours. Growth is temperature dependent. Temperatures between 8 and 15°C showed no development of larvae after sixty days. At 24°C the first molt occurs after just eight or nine days. A second molt follows just seven days later. At the third larval stage, D. insignis exits the host through the skin and must be in water. The larvae must be swallowed either by a paratenic host or the definitive host. Frogs often serve as paratenic hosts and Dracunculus insignis must wait for a definitive host to eat the frog. Definitive hosts for D. insignis are North American carnivores which are usually semi-aquatic. These include, mink, raccoon, otter, fisher, and occasionally domestic dogs. Upon reaching the definitive host, D. insignis undergoes two molts before reaching adulthood. The molt to the fourth stage takes place after one to two weeks after being ingested by the definitive host. Males will have completed the final molt to adulthood after approximately sixty days while females mature in sixty-five to seventy days. By 120 to 270 days, most females will have been fertilized and have their uterus full of larvae. (Crichton and Beverly-Burton, 1975; Panciera and Stockham, 1988; Roberts and Janovy, Jr., 2000)

Reproduction

Females may produce a phermomone to attract males. The male coils around a female with his curved area over the female genital pore. The gubernaculum, made of cuticle tissue, guides spicules which extend through the cloaca and anus. Mating occurs when a male inserts a spicule into the female's vulva and releases his sperm. Males use spicules to hold the female during copulation. Nematode sperm are amoeboid-like and lack flagella. The fertilized eggs develop into larvae within the uterus. By 120 to 270 days, most females will have been fertilized and have their uterus full of larvae. Females will create a lesion in their host from which they will send their larvae into the water by 300 to 365 days post-infection. Females release eggs for five to seven days after which they die and are absorbed into the host body. The rare occurrence of Dracunculus insignis males is due to their death directly following mating. (Barnes, 1987; Brusca and Brusca, 2003; Crichton and Beverly-Burton, 1975; Panciera and Stockham, 1988; Roberts and Janovy, Jr., 2000)

  • Parental Investment
  • pre-fertilization
    • provisioning

Behavior

Nematodes such as Dracaunculus insignis can swim intermittently. The worms are usually only able to move effectively when the pseudocoel is filled with fluid and hypertonic to to the surrounding media. (Barnes, 1987; Brusca and Brusca, 2003)

Communication and Perception

Nematodes within the Secernentea have phasmids, which are unicellular glands. Phasmids likely function as chemoreceptors. Females may produce pheromones to attract males.

Nematodes in general have papillae, setae and amphids as the main sense organs. Setae detect motion (mechanoreceptors), while amphids detect chemicals (chemoreceptors).

Food Habits

Dracunculus insignis is an endoparasite with individuals being found most often in the intramuscular connective tissue of the limbs as well as the subcutaneous tissue of the abdomen in the definitive host. The diet of both juveniles and adult females is composed of host tissue fluid and a small amount of blood. Pharyngeal glands and intestinal epithelium produce digestive enzymes. Extracellular digestion begins within the lumen and is finished intracellularly. Adult males, with their atrophied gut, do not feed. (Barnes, 1987; Brusca and Brusca, 2003; Roberts and Janovy, Jr., 2000)

  • Animal Foods
  • blood
  • body fluids

Predation

These parasites are usually not preyed on directly, but are ingested from host to host. (Barnes, 1987; Brusca and Brusca, 2003)

Ecosystem Roles

The life cycle of Dracunculus insignis involves at least two hosts: an intermediate copepod host, either Cyclops vernalis or Cyclops bicuspidatus thomasi. Definitive hosts for D. insignis are North American carnivores which are usually semi-aquatic. These include, mink, raccoon, otter, fisher, and occasionally domestic dogs.

Species Used as Host

Economic Importance for Humans: Negative

Dracunculus insignis does not parasitize humans. However, it does infect carnivores, including domestic dogs. A dog parasitized by D. insignis will exhibit subcutaneous swellings between three and five cm in diameter. Most often these can be found on the limbs, but they have been reported on the head of dogs. Dehydration, vomiting, diarrhea, and asthma are also common symptoms of infection. Infestation usually involves a trip to the veterinarian for removal of the parasite. The procedure for removing D. insignis involves placing the dog in water deep enough to cover the wounds thus causing the adult females to emerge from the swellings. This is followed by dissection to completely remove the parasites.

A close relative of Dracunculus insignis, D. medinensis (the Guinea worm) is responsible for a condition known as dracunculiasis in humans throughout much of Africa and the Middle East. Chemicals to kill the parasite are being tested on D. insignis in hopes of eradicating the problems caused by D. medinensis. (Eberhard, et al., 1990; Johnson, 1974; Panciera and Stockham, 1988)

Conservation Status

Contributors

Renee Sherman Mulcrone (editor).

Daniel Fargo (author), University of Michigan-Ann Arbor, Teresa Friedrich (editor), University of Michigan-Ann Arbor.

Glossary

Nearctic

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

agricultural

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.

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

carnivore

an animal that mainly eats meat

causes or carries domestic animal disease

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

chaparral

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.

chemical

uses smells or other chemicals to communicate

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.

ectothermic

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

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

forest

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

heterothermic

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.

marsh

marshes are wetland areas often dominated by grasses and reeds.

motile

having the capacity to move from one place to another.

mountains

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.

ovoviviparous

reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.

parasite

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

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

rainforest

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.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

scrub forest

scrub forests develop in areas that experience dry seasons.

sedentary

remains in the same area

sexual

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

suburban

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

swamp

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

tactile

uses touch to communicate

temperate

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).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

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.

savanna

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.

urban

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

References

Barnes, R. 1987. Invertebrate Zoology. Orlando, Florida: Dryden Press.

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

Carlson, B., V. Sasseville. 1984. Dracunculus insignis in fishers in New Hampshire. Journal of the American Veterinary Medical Association, 185: 1327.

Crichton, V., M. Beverly-Burton. 1975. Migration, growth, and morphogenesis of Dracunculus insignis (Nematoda: Dracunculoidea). Canadian Journal of Zoology, 53: 105-112.

Eberhard, M., F. Brandt, E. Ruiz-Tiben, A. Hightower. 1990. Chemoprophylactic drug trials for treatment of dracunculiasis using the Dracunculus insignis-ferret model. Journal of Helminthology, 64: 79-86.

Gibson, G., D. McKiel. 1972. Dracunculus insignis and larval Eustrongylides sp.in a muskrat from Ontario, Canada. Canadian Journal of Zoology, 50: 897-901.

Johnson, G. 1974. Dracunculus insignis in a dog. Journal of the American Veterinary Medical Association, 165: 372.

Michigan Department of Natural Resources, 2004. "North American Guinea Worm (Dranunculosis)" (On-line). Wildlife Diseases. Accessed September 23, 2004 at http://www.michigan.gov/dnr/0,1607,7-153-10370_12150_12220-27119--,00.html.

Panciera, D., S. Stockham. 1988. Dracunculus insignis infection in a dog. Journal of the American Veterinary Medical Association, 192: 76-78.

Roberts, L., J. Janovy, Jr.. 2000. Gerald D. Schmidt and Larry S. Roberts’ foundations of parasitology (Sixth Ed.). Boston, MA: McGraw-Hill.

University of Pennsylvania School of Veterinary Medicine, 2004. "Dracunculus insignis Homepage" (On-line). Diagnosis of Veterinary Endoparasitic Infections. Accessed September 23, 2004 at http://cal.vet.upenn.edu/dxendopar/parasitepages/filariidsandspirurids/d_insignis.html.

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