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.

Poultry red mite infestation still is an unsolved problem in poultry farms. Legal regulations, residue risks, and resistances limit chemical control of mites. Alternatives to chemical acaricides for control of poultry red mite are silica-based products, which have as a main constituent silicon dioxide. The acaricidal effect is attributed to sorptive properties of the particles, which result in the mite's death by desiccation. In the present study, the acaricidal efficacy of 12 products containing natural or synthetic silica, 9 in powder form, and 3 for liquid application was tested under laboratory conditions. Mite mortality was measured at several intervals and the mean lethal time (LT₅₀) determined by Probit analysis after Abbott's correction. The LT₅₀ values of the products significantly differed (Tukey's HSD p< 0.05). LT₅₀ values of powdery formulations ranged from 5.1 to 18.7 h and overlapped with those of the fluid ones which ranged from 5.5 to 12.7 h. In order to explain the differences in efficacy of the tested silica products, further characterizations were carried out. X-ray fluorescence, specific surface, cation exchange capacity (CEC), and water absorption capacity (WAC) were measured. Furthermore, electron microscopy was conducted and different products compared. Silicon dioxide content (ranging from 65 to 89% for powders and 57 to 80% for fluids) had no significant impact on efficacy, while specific surface and CEC (2.4-23.2 mEq 100(-1) g(-1) for powders and 18-30.8 mEq 100(-1) g(-1)) were positively and WAC (1.3-4.4 wt% for powders and 3.3-4.8 wt% for fluids) negatively related to the acaricidal efficacy. Influence of these parameters on acaricidal efficacy was significant according to the results of a stepwise regression analysis (p < 0.01).