Heterakis gallinarum

Geographic Range

Heterakis gallinarum is found worldwide in areas where galliform birds live. (Kaufmann, 1996)


Heterakis gallinarum is a parasite found in the cecum of numerous galliform birds including chickens, turkeys, and pheasants. The eggs of H. gallinarum are passed from the intestinal environment of the bird to the soil via the bird's feces. The eggs can survive in the soil for long periods of time, especially when a large amount of plant growth is present. Areas of soil with dense foliage better support the eggs by lessening the chances of damage from desiccation, extreme temperatures, or other organisms. Earthworms are often paratenic hosts for the eggs of H. gallinarum, with the eggs inhabiting the gut of the worm. (Kaufmann, 1996; Lund, 1960)

Physical Description

Heterakis gallinarum has a typical roundworm morphology with features such as a cuticle, an esophagus ending in a valved bulb, and three papillae-lined lips and alae. Alae, which run almost the entire length of the body, are ridges formed by the thickening of the cuticle that may act as receptors for molecules which stimulate reproduction. Adult female and male cecal worms differ in length, with the female (10 to 15 mm) generally being larger than the male (7 to 13 mm). Both sexes have a pointed tail, males having a precloacal sucker at the posterior end. The eggs of H. gallinarum are approximately 65-77 by 35-48 µm, with visibly thick, smooth shells. (Kaufmann, 1996; Olsen, 1986)

  • Sexual Dimorphism
  • female larger
  • Range length
    7 to 15 mm
    0.28 to 0.59 in


Embryonated eggs of H. gallinarum are ingested by their definitive host, a galliform bird, usually by either direct uptake from the soil or by ingestion of an earthworm or insect which has eaten an egg. Within the egg, the larvae develop to the infective second stage. Once eaten, the egg travels through the digestive system of the host until it reaches the intestine where it hatches. The juvenile then travels to the cecum where it molts twice before maturing into an adult. The duration of time it takes for an egg to molt is dependent upon the temperature at which the egg is kept; a higher temperature accelerates the process, while a lower temperature increases the number of days before the process occurs. (Anderson, 2000; Olsen, 1986)


Like most other nematode species, H. gallinarum is dioecious. Reproduction begins in the host's cecum when a male worm coils around a female worm, utilizing two uneven spicules on his posterior end to hold the female in place. This act involves internal fertilization with the male releasing his ameboid-like sperm into the female’s genital pore. Embryos are stored in the female uterus until their release into the host's feces. (Olsen, 1986; Roberts and Janovy, 2008)

Male worms are fully mature 14 days after they have infected the host. Females reach sexual maturity and start to lay eggs sometime between the age of 24 and 36 days. The number of eggs laid by a female cecal worm is dependent upon the species of bird it inhabits, but the average number of eggs laid is 211. (Lund and Chute, 1972; Lund and Chute, 1974; Olsen, 1986)

  • Average number of offspring
  • Range age at sexual or reproductive maturity (female)
    24 to 36 days
  • Average age at sexual or reproductive maturity (male)
    14 days

There is no parental care after the females lay eggs.

  • Parental Investment
  • pre-hatching/birth
    • provisioning


No data are available on the lifespan of adult worms, but the eggs of H. gallinarum have been observed to live up to five years in the soil, although this is likely rare. (Lund and Chute, 1974; Lund, 1960)


As in other nematodes, H. gallinarum has longitudinal muscles which in combination with the cuticle and pseudocoelom form a hydrostatic skeleton. By utilizing the force that the contraction of the longitudinal muscles creates, the cuticle shortens on one side then lengthens on the other, creating the diagnostic S-shaped movement of nematodes.

Juveniles of H. gallinarum normally reside in the lumen, but on occasion will travel to and enter either the cecal wall or cecal glands. (Anderson, 2000; Olsen, 1986; Roberts and Janovy, 2008)

Communication and Perception

Nematodes, including H. gallinarum, have chemosensory organs called amphids. Located anteriorly, these invaginations of the cuticle are made of many neurons which interpret and transmit incoming chemical signals. Heterakis gallinarum also has papillae, which are sensory structures surrounding the lip region. Behind the lip region are peg-like sensory structures which function both as chemoreceptors to detect chemicals, as well as mechanoreceptors to detect motion. Chemoreceptors are likely used in finding a mate, and sexual pheromones have been identified for over 40 nematode species. (Roberts and Janovy, 2008; Wright and Hui, 1976; Wright, 1977)

Food Habits

Heterakis gallinarum feeds on the cecal contents of the bird in which it resides. (Anderson, 2000)

  • Animal Foods
  • body fluids


Heterakis gallinarum is not directly preyed upon, but eggs which have been released into the soil can be eaten by other bird species, earthworms, and insects such as flies and grasshoppers. Often times, the eggs are brought to the surface of the soil by the movement of earthworms and other soil inhabitants, thus making them more susceptible to ingestion by those animals listed above. (Anderson, 2000; Lund, 1960)

Ecosystem Roles

Heterakis gallinarum is a parasite of galliform birds, feeding upon their cecal contents. Earthworms can serve as paratenic hosts for juveniles, allowing them to move from the soil to a bird's gut. Eggs of H. gallinarum can be a carrier of the disease causing protozoan Histomonas meleagridis. Birds can ingest infected H. gallinarum eggs and acquire H. meleagridis, resulting in blackhead disease. Blackhead disease affects mainly the liver and cecum of infected birds, causing lesions and ulcers that are eventually fatal. (Kaufmann, 1996; Olsen, 1986)

Species Used as Host
Commensal/Parasitic Species
  • Histomonas meleagridis

Economic Importance for Humans: Positive

There are no known positive effects of Heterakis gallinarum on humans.

Economic Importance for Humans: Negative

Heterakis gallinarum is economically important because it acts as a host for the protozoan H. meleagridis. Histomonas meleagridis causes histomoniasis, more commonly known as blackhead disease, in turkeys that have ingested H. gallinarum eggs with the parasite. Blackhead disease affects the liver and cecum of infected birds, causing enough damage to be fatal if left untreated. If many birds on turkey farms become infected and subsequently die, significant loss of profit can result for farmers. (Kaufmann, 1996; Olsen, 1986)

Conservation Status


Jackie Carron (author), University of Michigan-Ann Arbor, Heidi Liere (editor), University of Michigan-Ann Arbor, John Marino (editor), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor, Renee Mulcrone (editor), Special Projects.



Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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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.

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living in the southern part of the New World. In other words, Central and South America.

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

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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 or carries domestic animal disease

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


uses smells or other chemicals to communicate


having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.


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


union of egg and spermatozoan


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


having the capacity to move from one place to another.


found in the oriental region of the world. In other words, India and southeast Asia.

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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


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.


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.


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.


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.


Anderson, R. 2000. Nematode Parasites of Veretebrates: Their Development and Transmission. UK: CABI Publishing.

Kaufmann, J. 1996. Parasitic Infections of Domestic Animals: A Diagnostic Manual. Boston: Birkhauser.

Lund, E. 1960. Factors influencing the survival of Heterakis and Histomonas on soil. Journal of Parasitology, 46 (38): 38.

Lund, E., A. Chute. 1972. Heterakis and Histomonas infections in young peafowl, compared to such infections in pheasants, chickens, and turkeys. Journal of Wildlife Diseases, 8: 352-358.

Lund, E., A. Chute. 1974. The reproductive potential of Heterakis gallinarum in various species of galliform birds: Implications for survival of H. gallinarum and Histomonas meleagridis to recent times. International Journal for Parasitology, 4 (5): 455-461.

Olsen, O. 1986. Animal Parasites: Their Life Cycles and Ecology. New York: Dover Publications.

Roberts, L., J. Janovy. 2008. Foundations of Parasitology: 8th Edition. New York: McGraw-Hill.

Wright, K. 1977. Labial sense organs of the nematode, Heterakis gallinarum. The Journal of Parasitology, 63 (3): 528-539.

Wright, K., N. Hui. 1976. Post-labial sensory structures on the cecal worm, Heterakis gallinarum. Journal of Parasitology, 62 (4): 579-584.