Which two helminths have eggs that cannot be distinguished reliably by appearance?

Which two helminths have eggs that cannot be distinguished reliably by appearance?

• A. Ascaris lumbricoides and Fasciola hepatica
• B. Hymenolepis nana and H. diminuta
• C. Necator americanus and Ancylostoma duodenale
• D. Diphyllobothrium latum and Paragonimus westermani

Answer: (C)

Egg morphology cannot always tell you the species. For hookworms, the eggs of Necator americanus and Ancylostoma duodenale look essentially the same under standard stool microscopy—small, oval, thin-shelled with a developing embryo. Because of this near-identical appearance, you cannot reliably distinguish these two species just by egg shape or size. Differentiation usually requires growing the eggs to larvae in culture to observe larval characteristics or using molecular methods, or identifying the adult worms if available. Other pairs in the list have eggs that are more readily distinguishable by appearance: Ascaris lumbricoides eggs are larger and have a distinctive thick shell with a mammillated surface; Fasciola hepatica eggs are large and have characteristic bile-stained shells; Hymenolepis nana and H. diminuta eggs differ in size and overall morphology; Diphyllobothrium latum and Paragonimus westermani eggs have different shapes and surface features such as opercula or shell thickness.

Egg morphology cannot always tell you the species. For hookworms, the eggs of Necator americanus and Ancylostoma duodenale look essentially the same under standard stool microscopy—small, oval, thin-shelled with a developing embryo. Because of this near-identical appearance, you cannot reliably distinguish these two species just by egg shape or size. Differentiation usually requires growing the eggs to larvae in culture to observe larval characteristics or using molecular methods, or identifying the adult worms if available.

Other pairs in the list have eggs that are more readily distinguishable by appearance: Ascaris lumbricoides eggs are larger and have a distinctive thick shell with a mammillated surface; Fasciola hepatica eggs are large and have characteristic bile-stained shells; Hymenolepis nana and H. diminuta eggs differ in size and overall morphology; Diphyllobothrium latum and Paragonimus westermani eggs have different shapes and surface features such as opercula or shell thickness.