Experiments to produce cysts in cultures of Histomonas meleagridis—the agent of histomonosis in poultry

Abstract

Experiments were done with cultured trophozoite stages of different clonal strains (Histomonas meleagridis/Turkey/Austria/2922-C6/04 and H. meleagridis/Chicken/Hungary/5009-C2/05) of H. meleagridis in order to induce a cyst formation as it is known in other intestinal parasites. It was shown that the best multiplication of H. meleagridis occurred at 40°C in a full medium 199, when fetal calf serum and rice starch had been added. Under these conditions, numerous amoebic stages (8–12 µm in diameter) without and a few with flagellum were seen showing regular reproduction rates. When the conditions of culture were experimentally changed—and thus became worse—by decreasing the temperature, by deprivation of the medium from fetal calf serum and/or rice starch, and by changing the osmolarity, the pH, or the MgCl₂ concentration, many of the amoebic stages (containing starch granules) were destroyed, and several had obtained a spherical shape. If the culture conditions became even worse, smaller spherical stages occurred, which had only diameters of 4–7 µm and which appeared more condensed. Both spherical stages did not contain starch granules. All the previously seen stages disappeared constantly. Since a similar decrease of the optimal living conditions also occurs when intestinal or cloacal feces are deposited outside from the bird’s body, the results obtained here may underline the interpretation that some of the formerly amoebic stages are able to become large spherical stages and later small spherical stages. The large spherical stage would be some type of precysts while the smaller ones would represent true cysts.