Life Cycle
H. meleagridis reproduce by binary fission. The free trophozoites are very delicate and can survive only for a few hours in the external environment. However, when they are transmitted between flocks in the eggs of H. gallinarum, a cecal nematode, which in turn can be transmitted by earthworms that ingested the nematode eggs, they gain entry into the nematode eggs. The eggs with the trophozoites are passed out into the environment through the feces. In this way the trophozoites can remain viable for 1–2 years in the external environment. Within turkey flocks H. meleagridis is also known to be directly transmitted from bird to bird. Histomonads, either released from the heterakid nematode larvae in the ceca or after direct infection via the cloaca, and replicate rapidly in the cecal tissues. They migrate to the submucosa and muscularis mucosae and cause severe necrosis. The parasites then move to the liver through the vascular system. There they cause typical crater-like necrotic lesions. Mortality in turkey flocks can be very high (80-100%).
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