Schistosoma spp. Eggs: Spine Location by Species
Bench-card visuals for Schistosoma species identification by egg spine position: S. mansoni (large, prominent lateral spine), S. haematobium (terminal spine), and S. japonicum (small, rudimentary lateral spine or none).
Schistosoma egg spine: lateral = S. mansoni, terminal = S. haematobium, small/absent = S. japonicum
S. mansoni: 140-240 x 50-80 um - large, prominent lateral spine. In stool. S. haematobium: 110-170 x 40-70 um - terminal spine. In urine (or stool). S. japonicum: 70-100 x 55-65 um - smallest, nearly round, small rudimentary later...
140-240 x 50-80 um. Large, elongated. Prominent lateral spine at roughly the middle-to-posterior portion - this is the most recognizable feature. Contains a fully developed miracidium (embryonated). Found in stool - blood flukes in mesenteric venules of the large intestine. Endemic in Africa, Brazil, Caribbean, and Middle East. S. mansoni is also acid-fast positive in some preparations - do not confuse with AFB organisms.
110-170 x 40-70 um. Elongated, pointed at one end. Terminal spine at the abopercular (posterior) pole - the spine projects from the very tip. Found primarily in urine (bladder venule worms) - collect urine at noon when egg excretion peaks; may also be found in stool. Associated with urinary schistosomiasis, hematuria, and bladder cancer risk in endemic regions. Endemic in Africa and Middle East.
140-240 x 50-80 um. Large, elongated. Prominent lateral spine at roughly the middle-to-posterior portion - this is the most recognizable feature. Contains a fully de...
110-170 x 40-70 um. Elongated, pointed at one end. Terminal spine at the abopercular (posterior) pole - the spine projects from the very tip. Found primarily in urin...
Schistosoma species - what to look for
| Visual clue | Meaning | Student shorthand |
|---|---|---|
| Large elongated egg, prominent lateral spine, in stool | Schistosoma mansoni | Lateral spine at mid-to-posterior portion is pathognomonic for S. mansoni; examine stool with concentration method |
| Elongated egg, pointed terminal spine at one pole, in urine | Schistosoma haematobium | Terminal spine at the posterior tip; collect urine at noon peak; filter 10 mL urine through membrane filter for best yield |
| Small, nearly round egg, rudimentary or no visible spine | Schistosoma japonicum | 70-100 x 55-65 um - smallest and most round; small lateral spine may be absent or barely visible; found in stool; Far East distribution |
| Embryonated egg (miracidium visible inside) | Schistosoma egg - eggs are embryonated when passed | All Schistosoma eggs contain a fully developed miracidium when freshly passed - this distinguishes them from unembryonated trematode eggs |
| No operculum | Schistosoma feature - not an operculated trematode egg | Schistosoma eggs have no operculum - all other common trematode eggs (Paragonimus, Clonorchis, Fasciola, D. latum) are operculated |
Schistosoma species identification guide
| Pattern | What to call it | How to think about it |
|---|---|---|
| Large egg, prominent lateral spine, in stool | Schistosoma mansoni - positive | Report; praziquantel treatment; clinical correlation; baseline CBC and liver function |
| Elongated egg, terminal spine, in urine or stool | Schistosoma haematobium - positive | Report; praziquantel; urinalysis, renal function; imaging if long-standing infection (bladder wall changes) |
| Small nearly-round egg, small/no spine, in stool | Schistosoma japonicum - positive | Report; praziquantel (higher dose than other species); hepatic ultrasound in heavy or chronic infection |
- S. mansoni: large + prominent lateral spine + in stool. S. haematobium: terminal spine + in urine. S. japonicum: smallest + nearly round + minimal spine.
- No operculum on any Schistosoma egg - the absence of an operculum distinguishes Schistosoma from all common operculated trematode eggs.
- Collect at the right time from the right specimen: stool for S. mansoni/japonicum; urine at noon for S. haematobium.
Lateral spine = S. mansoni (stool). Terminal spine = S. haematobium (urine). Small, round, tiny spine = S. japonicum (stool). No operculum on any.