Liver flukes are a group of parasitic flatworms belonging to the class Trematoda, known for inhabiting the liver and bile ducts of various mammals, including humans. This article describes the observable features of adult liver flukes, providing insight into their typical size, shape, surface details, and distinct anatomical structures.
General Dimensions and Form
Adult liver flukes exhibit a distinct flattened, leaf-like, or lanceolate (spear-shaped) body. Their overall size varies significantly depending on the species, though many are large enough to be seen without magnification. For instance, the common liver fluke, Fasciola hepatica, typically measures between 15 to 30 millimeters (approximately 0.6 to 1.2 inches) in length and 10 to 15 millimeters (approximately 0.4 to 0.6 inches) in width, often described as having a broad, oval shape with a conical projection at the anterior end giving it “shoulders”. In contrast, species like Clonorchis sinensis and Opisthorchis viverrini are generally more slender, ranging from 10 to 25 millimeters (approximately 0.4 to 1 inch) in length and 3 to 5 millimeters (approximately 0.12 to 0.2 inches) in width. Their dorsoventrally flattened body allows them to navigate within the narrow bile ducts of their hosts.
Surface Characteristics and Color
The external covering of a liver fluke, known as the tegument, presents varied textures and colors. The tegument can appear smooth in some species, while others, like Fasciola hepatica, have small, backward-pointing spines distributed across their surface, which aids in attachment, movement, and feeding by eroding host tissue. The coloration of adult liver flukes is not uniform and can depend on the species, their physiological state, and the contents of their digestive system. They are often described as translucent, grayish, or pale. Some species, such as Fasciola hepatica, commonly appear reddish-brown or purple-gray, sometimes resembling leeches or blood clots, with ingested blood or bile influencing their color to a yellowish or darker hue.
Identifying Anatomical Marks
Adult liver flukes have key external anatomical features. All adult flukes possess two prominent muscular suckers: an oral sucker and a ventral sucker, also called the acetabulum. The oral sucker is located at the anterior end of the fluke and surrounds the mouth, which is used for feeding and attachment. The ventral sucker is positioned on the underside of the body, usually slightly posterior to the oral sucker, and is typically larger than the oral sucker, serving for strong adhesion to host tissues. For instance, in Fasciola hepatica, the oral sucker is found at the end of a cone-shaped projection, while the larger acetabulum is at the base of this cone.
Beyond the suckers, the internal structures can sometimes be discerned through the translucent body, contributing to the fluke’s overall visual pattern. The digestive system, a branched, blind-ended intestine (ceca), can often be faintly visible. The general outline of the reproductive organs, which are present in both male and female forms (hermaphroditic), may also be visible. These internal patterns, combined with the suckers and overall body shape, help identify adult liver flukes.