Morphology and Ultrastructural Characteristics of Platynosomum fastosum Kossack, 1910 Adults and Eggs

Abstract

Infection with Platynosomum fastosum, a liver fluke of domestic cats, can induce biliary obstruction and has been found to be associated with cholangiocarcinoma. To evaluate any new rational drugs, fundamental knowledges of parasite morphology are crucial but detailed morphology has not yet been investigated. Macroscopic, microscopic, and ultrastructural morphology of P. fastosum adult worms and eggs were evaluated. The adult fluke was reddish brown with a tamarind leaf-like body shape, 4.5mm in length and 1.5mm in width. Under scanning electron microscope (SEM), the tegumental surface of P. fastosum was spineless and covered with slender villous-like projections. Four types of papillae were found, and all were non-ciliated. P. fastosum fluke eggs were dark brown with an operculum and had a smooth eggshell surface with an inconspicuous posterior abopercular knob. From both fecal and bile samples, at least 3 types of eggs were present. The average size (mean±SD) of a typical P. fastosum egg was 44.2+1.7µm in length and 31.8+2.2µm in width. Under transmission electron microscope (TEM), tegument syncytium was composed of three layers. The first layer was an outermost trilaminate membrane covered by a glycocalyx. The second layer was tegumental cytoplasm composed of 2 types of tegumental granules, lysosomes, mitochondria and microtrabeculae. The third layer attached to a basal extracellular matrix with numerous basal membrane infoldings. This study revealed the first ultrastructural characteristics of P. fastosum adult and egg as a fundamental knowledge to use as basic criteria for assessment of anti-parasitic drug development in the future.