Morphological identification markers for distinguishing avian from mammalian Giardia species - do they need reconsideration?

The intestinal, parasitic protozoa comprising the genus Giardia are major a etiological agents of diarrhoeal disease in numerous vertebrates, including humans, livestock and domestic pets. In previous investigations, morphological characteristics, in particular ca udal flagellar length and asymmetry, have been used to distinguish avian fr om mammalian Giardia species, with scanning electron microscopy (SEM) often the technique of choice for observation. In this study, however, we observ ed considerable variation in caudal flagellar length and asymmetry, irrespe ctive of avian or mammalian host origin. In addition, SEM sample preparatio n and the age of trophozoite cultures caused increases in the number of tro phozoites with caudal flagellar length anomalies. Our findings, therefore, suggest that caudal flagellar characteristics are not reliable morphologica l markers for distinguishing Giardia species. In addition, the novel use of micromanipulation in establishing sub-clonal cultures of Giardia from sing le trophozoites was a highly accurate and successful microscopic technique.