Fasciola Gigantica: An observation of surface topography of the adult fluke by scanning electron microscope

Fasciola Gigantica is a liver like fluke that causes substantial economic loss in animal industry, particularly among cattles, buffaloes and sheep. The adult fluke has a leaf shape with the tapered anterior end. A full grown parasite is about 35 mm in length and 15 mm in width across the mid section. Its surface appears rough due to the presence of numerous spines. On the ventral surface the spines on the anterior part are small and closely-spaced except in the area immediately around the ventral sucker. Each spine has serrated edge with 16 to 20 sharp points, and it measures about 20 micro m in width and 30 micro m in height. On the mid redion the spines increase in size (up to 54 micro m in width and 58 micro m in height) as well as number, particularly towards the edges. Due to a larger size the spines serrated edges become less prominent, especially those on the lateral aspect. Towards the posterior the spines progressively decrease in both size and number. The tegument between the spines appears corrugated with transverse ridges alternated with troughs. At higher magnification the ridges is highly invaginated with mesh work of interlacing microfolds penetrated by variable size pits. The degree of invagination is equally extensive throughout the entire surface. In some areas, between spines there are sensory papillae, each appearing as a small dome about 4-6 micro m in diameter with a nipple like tip; some domes may, however, lack nipples. These papillae usually occur in clusters, each having between 2 and 3 up to 10 and 15 papillae per group. Those on the lateral aspect and around the suckers tend to be more numerous and larger in size, as well as having more papillae per cluster. Both the oral and ventral suckers have thick rims covered with thick transverse folds which are, in turn, surrounded by rings of clustered papillae, short serrated spines, and pores of gland cells. The dorsal surface exhibits similar surface features, but the spines and papillae appear less numerous and having smaller sizes, and the invagination is less extensive than on the ventral aspect.