Which pair of helminths cannot be reliably differentiated by the appearance of their eggs?

Which pair of helminths cannot be reliably differentiated by the appearance of their eggs?

• 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)

The key idea here is that not all parasite eggs are easily told apart under routine microscopy; some pairs look so similar that egg appearance alone can’t reliably distinguish them. The two hookworms, Necator americanus and Ancylostoma duodenale, produce eggs that are virtually indistinguishable when seen in stool samples. They are both oval, thin-shelled eggs of comparable size with developing embryos that look the same under standard exam methods, so you can’t reliably tell which species produced the egg just by its appearance. To separate them, you’d need to culture the eggs to generate larvae (rhabditiform or filariform) or use molecular methods, or identify the adult worms if possible. The other pairs have more distinctive egg features: for example, Ascaris lumbricoides eggs differ markedly in shell texture and size from Fasciola hepatica eggs; Hymenolepis nana and H. diminuta eggs differ in size, making them distinguishable; and Diphyllobothrium latum and Paragonimus westermani eggs have differing sizes and shell characteristics that allow reliable identification.

The key idea here is that not all parasite eggs are easily told apart under routine microscopy; some pairs look so similar that egg appearance alone can’t reliably distinguish them.

The two hookworms, Necator americanus and Ancylostoma duodenale, produce eggs that are virtually indistinguishable when seen in stool samples. They are both oval, thin-shelled eggs of comparable size with developing embryos that look the same under standard exam methods, so you can’t reliably tell which species produced the egg just by its appearance. To separate them, you’d need to culture the eggs to generate larvae (rhabditiform or filariform) or use molecular methods, or identify the adult worms if possible.

The other pairs have more distinctive egg features: for example, Ascaris lumbricoides eggs differ markedly in shell texture and size from Fasciola hepatica eggs; Hymenolepis nana and H. diminuta eggs differ in size, making them distinguishable; and Diphyllobothrium latum and Paragonimus westermani eggs have differing sizes and shell characteristics that allow reliable identification.