Tritrichomonas foetus is a serious veterinary pathogen that causes bovine trichomonosis, a sexually transmitted disease that eventually leads to abortion and infertility. T. foetus has a simple life cycle that consists of only a trophozoitic form. During unfavorable environmental conditions, the trophozoites, which are polar and flagellated, can adopt a spherical shape and internalize their flagella. These rounded organisms are known as pseudocysts. Although it is currently assumed that T. foetus pseudocyst formation is reversible and that it represents a response to stressful conditions, there are no reports showing the presence of this form in vivo. For this reason, the aim of this study was to verify whether T. foetus pseudocysts are encountered in naturally infected bulls. Towards this goal, fresh preputial samples obtained from seven mature bulls that were naturally infected with T. foetus were analyzed using complementary techniques, such as video microscopy, fluorescence microscopy, scanning and transmission electron microscopy. The analyses revealed that approximately 55% of the parasites were in pseudocyst form in each preputial sample, whereas approximately 25% of T. foetus displayed pear-shaped bodies. Previous research demonstrated that in vitro T. foetus pseudocysts are able to divide by a budding process. Here, this division mode was observed in approximately 20% of fresh T. foetus obtained from preputial bovine samples. Thus, this study shows that in infected bulls, pseudocysts are present and occur more frequently than the pear-shaped parasites.
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