Heterakis gallinarum

Taxonomy, Common Name, Disease

Scientific name - Heterakis gallinarum

Disease - histomoniasis

Historical

Thought to have been brought into the U.S. in imported ringnecked pheasants.

Hosts

Domestic chickens and related birds.

Distribution

Worldwide.

Life Cycle

The eggs develop to the infective stage in 12 to 14 days at 22 C and can remain infective for 4 years in soil. Infection occurs when eggs are eaten. The second stage juveniles hatch in the gizzard or duodenum and pass down to the ceca. Most complete their development in the lumen, but some penetrate the mucosa, where they remain for 2 to 5 days without further development. Returning to the lumen they mature, about 14 days after infection. If eaten by an earthworm, the juvenile may hatch and become dormant in the worm's tissues, remaining infective to chickens for at least a year. Since the nematodes do not develop further until eaten by a bird, the earthworm is a paratenic host.

Symptoms-Pathogenicity

In heavy infections the cecal mucosa may thicken and bleed slightly. Generally speaking, Heterakis is not highly pathogenic in itself. However, a flagellate protozoan, Histomonas meleagridis, is transmitted between birds within eggs of the nematode. This protozoan is the etiological agent of histomoniasis, a particularly serious disease in turkeys. The protozoan is eaten by the nematode and multiplies in the worm's intestinal cells, in the ovaries, and, finally, in the embryo within the egg. Hatching of the worm within a new host releases Histomonas. One parasite acts as a true intermediate host and vector of another.

Management

As a result of the longevity of the eggs, and the ability of earthworms to serve as paratenic hosts, it is difficult to eliminate Heterakis from a domestic flock.

Diagnosis - is by finding the eggs in the feces of its host. Nematodes can be effectively eliminated with mebendazole. Usually a flock of birds is routinely fed the drug in feed or water. Rearing birds on hardware cloth that permits passage of feces, will eliminate the parasite from the flock.

Importance

Transmission of the protozoan Histomonas.

Characteristics

Three large lips and a bulbar esophageal swelling are found in this genus, as are lateral alae. Males are as long as 13 um and possess wide caudal alae supported usually by 12 pairs of papillae. The tail is sharply pointed, and there is a prominent preanal sucker. The spicules are strong and dissimilar, and a gubernaculum is not present. Females are typical pinworms with the vulva near the middle of the body and with a long pointed tail.

References

  1. Schmidt, G.S., and L.S. Roberts. 1989. Chapter 28. Order Oxyurata: Pinworms. in Foundations of Parasitology. Times Mirror/Mosby College Publishing. St. Louis. 750 pages.
  2. Levine, N.D. 1968. Nematode Parasites of Domestic Animals and of Man. Burgess Publishing Company. Minneapolis. 600 pages.