Lightmicroscopic Observations on Structure and Division of Histomonas meleagridis (Smith)*

Abstract

SYNOPSIS. Culture forms and lumen‐dwelling phases of the ameboflagellate Histomonas meleagridis, which are structurally indistinguishable from each other, have a single flagellum. Their well‐developed pelta is connected to the anterior segment of the broad, spatulate axostylar capitulum, applied to the left‐ventral surface of the nearly spheroid or somewhat ellipsoid or ovoid nucleus. The capitulum narrows into a very slender axostylar trunk that tapers to a fine point and does not project beyond the body surface. The parabasal apparatus consists of a V‐shaped parabasal body and a large parabasal filament. A new flagellum appears early during division and soon approaches its full length. The 2 flagella persist thruout division and each becomes the locomotory organelle of a daughter histomonad. The arms of the parental parabasal body appear to separate, each going to 1 of the daughter mastigont systems; some parabasal material is lost early in division. The 2nd arm is regenerated in each daughter parabasal body. The large parabasal filament seems not to be retained in the parental mastigont system, and new filaments are seen at both poles before 2 daughter nuclei are formed. The old axostyle degenerates from the anterior toward the posterior end; at the same time lamellar primordia of the daughter pelta‐axostyle complexes appear in the separating mastigont systems that are connected by an extranuclear spindle during the entire division process. The structure and taxonomic status of H. meleagridis are discussed in the light of this and previous studies.

Phylogenetic Position of the Trichomonad Parasite of Turkeys, Histomonas meleagridis (Smith) Tyzzer, Inferred from Small Subunit rRNA Sequence1

“…The pelta is a long, wide and crescent‐shaped structure that supports the anterior end of the parasite. All these specific characters are identical to those described in previous cytological studies (Honigberg and Bennett 1971; Rybicka, Honigberg, and Holt 1972; Schuster 1968) and allow us to confirm the identification of our strain as H. meleagridis. …”

“…In culture, H. meleagridis exhibits the morphology of the “lumen‐dwelling form”. The structure and division of the flagellated forms of H. meleagridis are well known from light (Bishop 1938; Dobell 1940; Honigberg and Bennett 1971; Honigberg and Kuldova 1969; Lund, Augustine, and Chute 1967; Tyzzer 1919, 1934; Wenrich 1943) and electron microscopy (Rybicka, Honigberg, and Holt 1972; Schuster 1968). Under the light microscope, H. meleagridis possesses an amoeboid morphology and it has been commonly placed among the Rhizopoda including Entamoeba and its closest relatives.…”

Passive immunization againstHistomonas meleagridisdoes not protect turkeys from an experimental infection

“…A second group of birds (group IM) was immunized by intramuscular injection with dead H. meleagridis antigens derived from infected livers and caeca. This choice of immunizing material should generate antibodies against all in vivo stages as the parasite appears in different stages within its host (Lee et al, 1969;Honigberg & Bennett, 1971) but it resulted in significantly higher mean lesion scores of both the liver and caeca than those of the IC and the negative control group*although, as far as we could judge the mortality at 10 days post challenge, only one of 10 birds died of histomonosis. Furthermore, the mean lesion scores of the surviving birds were higher in the IM group than in the INC (infected non-immunized control) group, suggesting that immunity induced by dead antigens is not protective against histomonosis.…”

Experimental Histomoniasis in the Guinea Fowl, Numida meleagris*

“…Natural or experimental infections with H . meleagridis have been reported from at least 16 galliform species in addition to the domestic turkey and chicken (2, 3, 15, 33, 35; see 16), but detailed studies of histomoniasis in many of these birds are lacking.…”