Manual of basic techniques for a health laboratory - libdoc.who.int

140 Manual of basic techniques for a health laboratoryNecator americanus (Fig. 4.70)Almost identical to the eggs of Ancylostoma duodenale (see Fig. 4.42).Size: 60–80mm (slightly longer than A. duodenale).Shape: oval with rounded flattened poles (more flattened than in A. duodenale).Content: always contains at least eight cells (never four like A. duodenale in freshstools).Fig. 4.70 Necator americanuseggFig. 4.71 Opisthorchisfelineus eggsOpisthorchis felineus (Fig. 4.71)Similar to the eggs of Clonorchis sinensis (see Fig. 4.49).Size: 25–35mm (identical to C. sinensis).Shape: slightly narrower at the base and with less shouldering than C. sinensis; someeggs are asymmetrical.Operculum: less overlap than C. sinensis.Boss: rarely visible.Content: a ciliated embryo.It is very difficult to differentiate between the eggs of O. felineus, C. sinensis, Heterophyesheterophyes and Metagonimus yokogawai:●●●●O. felineus: narrow, often asymmetrical, boss rarely visible.C. sinensis: squat shape, operculum with distinct overlap.H. heterophyes: squat shape, darker colour.M. yokogawai: thicker shell.Fig. 4.72 Paragonimuswestermani eggParagonimus westermani (Fig. 4.72)Eggs mainly found in sputum (if swallowed they pass into the stools).Size: 65–120mm (smaller than the eggs of Fasciolopsis buski).Shape: oval, often slightly flattened on one side.Operculum: quite distinct, with an obvious rim.Shell: distinct thickening at the opposite end to the operculum.Content: clear central space surrounded by squarish cells.Colour: golden brown.Fig. 4.73 Schistosoma boviseggSchistosoma bovis (Fig. 4.73)Eggs found in the stools of patients who have eaten infected beef.Size: about 200mm.Shape: spindle-shaped, with narrowed extremities extending beyond the embryo.Spine: long terminal spine.Content: small round embryo lying in the centre of the egg but not filling it.S. bovis does not cause disease in humans.Schistosoma haematobium (Fig. 4.74)Eggs found in urine (for detection, see section 7.2.8) and occasionally in stools.Size: 110–150mm.Shape: oval, with one well-rounded pole.Spine: terminal and situated at the other pole.