Question
Egg of schistoma hematobium.
Answer
The egg of Schistosoma haematobium is a key diagnostic feature distinguishing it from other schistosome species, characteristically found in urine (rather than stool, as with the intestinal schistosome species) — reflecting the adult worm pairs’ characteristic habitat in the venous plexus of the urinary bladder (vesical venous plexus).
Morphology: a large, oval/elongated egg (~110–170 μm by 40–70 μm), with a characteristic prominent terminal spine at one pole — this terminal spine is the key distinguishing feature from S. mansoni eggs, which instead have a lateral spine, and from S. japonicum eggs, which have only a small, inconspicuous lateral knob/spine. The egg shell is otherwise smooth and non-operculated (unlike trematode eggs of the liver/lung fluke type).
Passage: eggs are laid by the female worm within small venules of the bladder wall, and their spine helps them work their way through the tissue toward the bladder lumen (aided also by enzymes secreted by the miracidium within, which cause local tissue inflammation/erosion), from where they are shed in urine — typically most concentrated in terminal urine (the last portion voided), an important collection consideration for maximizing diagnostic yield.
Clinical correlation: chronic bladder wall egg deposition provokes granulomatous inflammation, fibrosis, and calcification, causing terminal haematuria (the classical presenting symptom), dysuria, and, over years, an increased risk of squamous cell carcinoma of the bladder — a well-recognized long-term complication of chronic untreated S. haematobium infection.
Laboratory diagnosis: urine microscopy (ideally terminal urine, collected around midday when egg excretion peaks) for the characteristic terminal-spined egg; urine filtration/concentration techniques improve sensitivity; cystoscopy with bladder biopsy can also demonstrate eggs in tissue in chronic cases with low urinary egg output.