Reading File
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Reading File
Finding Sources
The textbook passage is very revealing. Here is the full answer:
Answer: Fecal Egg Method NOT Used for Which Nematodes?
The question asks which nematodes cannot be detected by the fecal egg method (examination of stool for eggs). This method works for intestinal nematodes that shed eggs into the gut lumen. Two types of organisms on this list do NOT shed detectable eggs in feces:
The Correct Answers Are:
1. Wuchereria bancrofti (primary answer)
- This is a filarial nematode (tissue nematode), not an intestinal worm
- It lives in the lymphatic system, not the GI tract
- Diagnosis is made by detecting microfilariae in peripheral blood (ideally collected between 10 PM - 4 AM due to nocturnal periodicity), NOT by fecal examination
- As confirmed by Medical Microbiology 9e: "filariae such as Wuchereria bancrofti have nocturnal periodicity in which greater numbers of microfilariae are found in the peripheral blood at night"
2. Trichinella spiralis
- Also a tissue nematode - larvae encyst in skeletal muscle, not the intestinal lumen
- Diagnosis is by muscle biopsy showing encysted larvae, or serology
- No eggs are passed in stool
3. Enterobius vermicularis (pinworm) - partial exception
- Does NOT reliably shed eggs in feces in detectable quantities
- Diagnosed by the scotch tape/cellophane tape test applied to the perianal region (females lay eggs on perianal skin at night), NOT by fecal egg count
- Eggs are rarely found on routine stool examination
Summary Table
| Organism | Why Fecal Egg Method Fails |
|---|---|
| Ancylostoma duodenale | Intestinal nematode - eggs DETECTED in feces (method works) |
| Trichocephalus trichiurus | Intestinal nematode - eggs DETECTED in feces (method works) |
| Ascaris lumbricoides | Produces vast numbers of eggs in stool - method works very well |
| Wuchereria bancrofti | Filarial/lymphatic - diagnosed by blood smear for microfilariae |
| Enterobius vermicularis | Perianal egg deposition - diagnosed by Scotch tape test |
| Opisthorchis felineus | A liver fluke (trematode) - eggs ARE found in feces |
| Trichinella spiralis | Tissue/muscle nematode - diagnosed by muscle biopsy |
The best single answer is Wuchereria bancrofti - it is a filarial nematode (not intestinal) whose eggs/larvae are never shed in feces. Trichinella spiralis and Enterobius vermicularis are also poor candidates for fecal egg detection, but if this is a single-answer MCQ, Wuchereria bancrofti is the most clear-cut answer since it has no GI phase where eggs would appear in stool.
Source: Medical Microbiology 9e, Ch. 70 & 74 - Laboratory Diagnosis of Parasitic Disease
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