Histomonas meleagridis
Phylum Sarcomastigophora
Order Trichomonadida
Family Monocercomonadidae
Histomonas meleagridis
Background
-Histomonas meleagridis is a cosmopolitan parasite.
-It infects chickens, turkeys, peafowl, and pheasant.
-Causes a disease known as blackhead, infectious enterohepatitis, or histomoniasis
-Disease effects turkey more than chickens
-This parasite causes great economic loss for the USDA
Definitive host(s): chicken, turkeys, peafowl, and
pheasant
Intermediate host: Heterakis gallinarum (a cecal
nematode)
Geographic Range: anywhere the definitive host are found
Morphology:
-Environmental factors influence the size and shape of the parasite in its
life stages.
-The life cycle does not have a cyst stage present.
-The parasite is found within the lumen of the cecum.
-Life stages are amoeboid 5 to 30 microns in diameter usually with one flagellum.
-The nucleus is vesicular and has a distinct endosome.
-There is a clear ectoplasm and granular endoplasm.
-Food vacuoles are present and may contain host blood cells.
-Sexual stages do not occur in the life cycle.
-Histomonas meleagridis divides by binary fission.
Life cycle
-Being transported within the egg of H. gallinarum carries out
transmission of H. meleagridis.
-It undergoes development and multiplication within H. gallinarum.
-H. meleagridis is ingested by the cecal nematode and the flagellates enter
the nematode's intestinal cells.
-Within the intestinal cells it will multiply then go to the pseudocoel and invade the
germinative area of the nematode's ovary.
-In the ovary it will feed and multiply, then migrate down the ovary and penetrate the
oocysts.
-H. meleagridis is passed out of the worm and the bird in the feces.
-Inside the egg it will penetrate juvenile nematode tissue.
-Infected nematode eggs can last up to two years in soil.
-The worm eggs are eaten by the proper definitive host and hatch in the intestine.
-The juvenile Heterakis migrates toward the cecum.
-Here Histomonas leaves Heterakis and resides in the host bird.
-Earthworms serve as a paratenic host for Heterakis and Histomonas.
-The earthworms will eat the nematode eggs.
-The eggs hatch releasing second stage juveniles that become dormant in the earthworm.
-When the earthworms are eaten by the bird, Heterakis juveniles are released
causing infection by two different parasites.
-Heterakis eggs and infected earthworms survive long periods of time in the soil.
Pathogenesis
-Turkeys are most susceptible between 3 and 12 weeks of age.
-Chickens are less likely to be infected by Histomonas meleagridis.
-Lesions are present in the cecum and liver.
-Perforations of the cecum and peritonitis can occur.
-The cecum is enlarged and inflamed.
-Liver lesions will have white and green areas of necrosis.
-Symptoms of infected birds are droopiness, ruffled feathers, yellowish diarrhea, hanging
wings and tails.
-The skin on the head turns black is some instances (caused by secondary bacterial
infections).
-Birds that survive infection are immune for life
Diagnosis
-Detection of cecal and liver lesions
Treatment
-Use of nitroimidazoles and phenylarsonis acid derivatives.
-These suppress, inhibit, or cure the disease.
-To prevent future outbreaks the use of nematocides such as mebendazole, cambendazole, and
levanisole are effective.
Control
-Keep young birds off the ground using hardware cloth or on dry ground.
-Control of Heterakis populations.
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