Members of the family Trichomonadidae, mainly Trichomonas gallinae and Tetratrichomonas gallinarum, represent
important parasites in birds with worldwide presence, since being reported in the 19th century. Especially Columbiformes,
Falconiformes and Strigiformes can be severely affected by trichomonads, whereas the majority of infections in Galliformes
and Anatiformes are subclinical although severe infections are occasionally reported. With the recent appearance of deadly
infections in wild Passeriformes the protozoan parasite T. gallinae obtained greater attention which will be addressed in this
review. Although light microscopy remains the method of choice to confirm the presence of trichomonads molecular studies
were introduced in recent years, in order to characterize the parasites and to establish relationships between isolates.
Isolation of trichomonads is a prerequisite for detailed in vitro and in vivo studies and different media are reported to obtain
suitable material. The limited information about virulence factors will be reviewed in context with the pathogenicity of
trichomonads which varies greatly, indicating certain strain heterogeneity of the parasites. Options for treatment
characterized by the leading role of imidazoles whose activity is sometimes hampered by resistant parasites remains
a challenge for the future. Introducing more standardized genetic studies and investigations concentrating on the
host-pathogen interaction should be helpful to elucidate virulence factors which might lead to new concepts of treatment.