Structure of a Nonpathogenic Histomonad from the Cecum of Galliform Birds and Revision of the Trichomonad Family Monocercomonadidae Kirby*

Abstract

SYNOPSIS. The nonpathogenic flagellate from the cecum of fowl, hitherto known as Histomonas wenrichi Lund, is an actively ameboid organism equipped with 4 flagella. Three of the flagella, subequal in length, are applied to one another for a short distance anterior to their origin in the kinetosomal complex and typically terminate in knob‐like expansions; the 4th flagellum originates independently of the others and ends in a fine filament. A short, wide pelta is joined to the anterior part of the broad, spatulate axostylar capitulum applied to the left‐ventral surface of the ellipsoidal, spheroidal, or ovoidal nucleus. Posterior to the nucleus the capitulum narrows into a slender axostylar trunk, which does not project beyond the body surface. The parabasal body, associated with a long, stout parabasal filament, is dorsal and to the right of the nucleus. On the basis of the flagellar number, the parasite is placed in a new genus Parahistomonas. A new subfamily, Protrichomonadinae, is created within the appropriately emended trichomonad family Monocercomonadidae for Parahistomonas wenrichi (Lund) comb. nov. as well as for Histomonas meleagridis (Smith) and Protrichomonas legeri (Alexeieff).

Molecular identification and phylogenetic relationships of trichomonad isolates of galliform birds inferred from nuclear small subunit rRNA gene sequences

“…Therefore, these observations strongly suggested that type III isolates could only correspond to Parahistomonas wenrichi. Indeed, all these data confirmed the morphological, culture, and pathogenic features of this microorganism described in previous studies (Lund 1963;Honigberg and Kuldova 1969). However, P. wenrichi is characterized by the presence of four flagella and any flagellum was not clearly recognized in the H. meleagridis type III isolates (Van der Heijden et al 2006) as well as in the isolate AL411F6 (Fig.…”

“…It has been previously shown that in living organisms as well as in hematoxylin and protargol stainings of cell preparations, the flagella of P. wenrichi were extremely difficult to observe and numerous cells only exhibited one visible flagellum after staining or a bundle in the center of the cell that could correspond to the four flagella as shown Fig. 1d (Lund 1963;Honigberg and Kuldova 1969;McDougald 2003). In addition, the cellular cycle of this trichomonad remains unknown and the existence of an aflagellated form during this cycle cannot be excluded as it has been described for H. meleagridis (Lund et al 1967).…”

“…Indeed, P. legeri also possesses four flagella (three anterior flagella and an intracytoplasmic recurrent flagellum), a similar size to that of P. wenrichi, and an amoeboid tendency. Thus, Honigberg and Kuldova (1969) suggested that these two species would have to be considered as congeneric, with Protrichomonas as the type genus. In further studies, it would be of great interest to obtain the SSU rRNA gene sequence of P. legeri that could be now compared to that of P. wenrichi in order to test the proposed synonymy of Parahistomonas and Protrichomonas.…”

“…Subsequently, Lund (1963) created a new species wenrichi in the genus Histomonas for these larger 4-flagellate forms which were considered as non-pathogenic for fowl. Ultimately, Honigberg and Kuldova (1969) supported the taxonomic considerations by Lund (1963) while suggesting the creation of a new genus, Parahistomonas, for these larger organisms on the basis of the number of flagella.…”

Genotyping ofHistomonas meleagridisisolates based on Internal Transcribed Spacer-1 sequences

“…Although the organism, like H. meleagridis, ingested rice particles, it proved impossible to grow or subculture the organism in Dwyer's medium. Morphologically, the organism is different from Tetratrichomonas gallinarum, Trichomonas gallinae, or Histomonas wenrichii (Honigberg & Kuldova, 1969). Sequence analysis of the ssu rRNA gene revealed a close phylogenetic relationship between this organism and the human pathogen D. fragilis and with Tritrichomonas foetus, which is the common ancestor of D. fragilis and H. meleagridis (Gerbod et al ., 2001) at a slightly larger distance.…”