Ascaris lumbricoides: Mammillated and Decorticate Eggs
Bench-card visuals for Ascaris lumbricoides eggs: the bile-stained mammillated (bumpy) fertile egg - the most recognizable helminth egg in clinical parasitology - and the decorticate variant that has lost its outer coat.
Ascaris lumbricoides egg: fertile mammillated vs. decorticate/infertile
Fertile egg: oval 45-70 um, thick bile-stained mammillated outer coat (bumpy), thick inner shell, unsegmented single cell. Decorticate: same fertile egg without mammillated coat - smooth surface, common after zinc sulfate flotatio...
45-70 um. Oval. Thick bile-stained (golden-brown) mammillated outer coat - the bumpy exterior is pathognomonic. Thick inner shell. Single unsegmented cell inside. The most common and recognizable form in clinical stool. High daily egg output (up to 200,000/day) means concentration is often not necessary for heavy infections.
Decorticate: fertile egg that has lost its mammillated coat - oval, thick inner shell, smooth surface. Common after zinc sulfate flotation or mechanical processing. Infertile: more elongated (80-90 um), irregular outline, disorganized granular content - the most difficult Ascaris egg to recognize. Finding classic mammillated eggs in the same specimen is the best confirmation for decorticate and infertile forms.
45-70 um. Oval. Thick bile-stained (golden-brown) mammillated outer coat - the bumpy exterior is pathognomonic. Thick inner shell. Single unsegmented cell inside. Th...
Decorticate: fertile egg that has lost its mammillated coat - oval, thick inner shell, smooth surface. Common after zinc sulfate flotation or mechanical processing....
What to look for in stool
| Visual clue | Meaning | Student shorthand |
|---|---|---|
| Oval, thick mammillated (bumpy) outer coat, bile-stained, 45-70 um | Ascaris lumbricoides fertile egg | Pathognomonic - no other common intestinal helminth egg has a thick bumpy outer coat at this size |
| Oval, thick inner shell, smooth outer surface | Decorticate Ascaris egg | Coat lost during concentration; look for classic mammillated eggs in same prep for confirmation |
| Elongated, irregular outline, disorganized granular content | Possible infertile Ascaris egg | Hardest form to ID alone; correlate with clinical context and presence of fertile eggs in specimen |
| Single unsegmented (non-segmented) cell | Ascaris fertile egg feature | No morula or larva - unlike hookworm (morula inside) or Enterobius (larva inside) |
| No outer coat, thick inner shell, oval outline | Decorticate vs. other helminth eggs | Decorticate Ascaris egg can resemble hookworm or other thin-shelled eggs - size (larger, 45-70 um) helps distinguish |
Ascaris lumbricoides egg identification guide
| Pattern | What to call it | How to think about it |
|---|---|---|
| Oval, thick mammillated outer coat, bile-stained, 45-70 um | Ascaris lumbricoides fertile egg - positive | Report and treat; anthelmintic therapy indicated; screen household contacts in endemic settings |
| Oval, smooth outer surface, thick inner shell | Decorticate Ascaris egg - consistent with positive | Confirm by finding mammillated eggs in same prep; report as A. lumbricoides consistent with; clinical correlation required |
| Elongated, irregular, disorganized granular content | Possible infertile Ascaris egg | Do not report on single infertile egg alone; correlate with clinical context and presence of fertile eggs; confirm per lab SOP |
- Mammillated (bumpy) bile-stained outer coat on an oval egg = Ascaris lumbricoides fertile egg - pathognomonic.
- Decorticate eggs (smooth, no outer coat) are common after concentration methods - look for classic eggs in the same prep.
- Infertile eggs are elongated and irregular - difficult to ID alone; clinical context and co-detection of fertile eggs is required.
Bumpy bile-stained oval = Ascaris. Decorticate (smooth oval, thick shell) = common after flotation. Infertile = elongated and irregular. Largest common intestinal helminth egg.