Light and transmission electron microscopic studies on trophozoites and cyst-like stages of Histomonas meleagridis from cultures

Abstract

The present study deals with Berlin strains of Histomonas meleagridis, the specimens of which were cultivated in Dwyer's medium. The light and electron microscopic examination revealed that the cultivated trophozoite stages (reaching about 10 mum in size) appeared more or less spherical, although their surface (covered by a single membrane) showed amoeba-like waves. All stages were uni-nucleated and reproduced by binary fission with an extranuclear spindle apparatus. Some trophozoites appeared ovoid and possessed a single flagellum with a typical microtubular 9 x 2 + 2 arrangement. Furthermore, the latter were characterized by an inner row of typical microtubules (remnant of an axostyle) and a Golgi apparatus (both adjacent to the nucleus), multivesicular structures, hydrogenosomes, and many food vacuoles containing either starch grains or bacteria. Their cytoplasm was densely filled with glycogen granules and ribosomes. Similar stages were also documented in the caeca and cloaca of chicken when being inoculated (via cloaca) with such culture stages. In addition to these typical trophozoites, the cultures contained a low number of 10-mum-sized spherical cyst-like stages with a surrounding amorphous layer. The cytoplasm of some of these cyst-like stages-when studied by electron microscopy-appeared with two membranes or had formed an amorphic, cyst-wall-like layer at their surface, apparently corresponding to their light microscopical appearance. Such stages might be involved in transmission from one host to another and probably have been missed before in microscopical examinations of infected poultry.

Dientamoeba fragilis, the Neglected Trichomonad of the Human Bowel

“…He stated that it was "inconceivable that D. fragilis would have a cyst stage," while "Histomonasits closest relative also has no cysts" (2). Recently, cyst-like stages of H. meleagridis have been reported (66,67). These forms are similar to those described by Stark et al (62) for D. fragilis: completely spherical compact structures with a size of 4 m. These cyst-like forms were thought to represent the initial stages of true cyst formation that can withstand harsh environmental conditions (67,68), although the infectivity of these structures is yet to be confirmed.…”

Description of Dientamoeba fragilis Cyst and Precystic Forms from Human Samples

“…Dobell also stated that it was inconceivable that D. fragilis would have a cyst stage while "Histomonas-its closest relative-also has no cysts." However, recent reports describe precystic and cyst forms of Histomonas meleagridis (26,27). These stages are completely spherical compact structures with a size range of 4 to 7 m in diameter, have been demonstrated to survive adverse conditions, including extreme acid conditions (pH 2) (27), and are morphologically similar to the precystic form of D. fragilis described herein.…”

Quantification of parasite shedding and horizontal transmission parameters inHistomonas meleagridis-infected turkeys determined by real-time quantitative PCR

“…The non-vector-mediated transmission is supported by the survival of H. meleagridis for up to 9 hours in non-chlorinated water or faecal matter (Lotfi et al, 2012). In addition, a possible role for cyst-like structures, which have recently been identified in histomonas cultures (Munsch et al, 2009;Zaragatzki et al, 2010) in horizontal transmission, cannot be discarded. These "cysts" might cause infection by both, the oral and cloacal route.…”