A patient recently returned from sub-Saharan Africa presents with painless haematuria. This structure was found on microscopy of urine. It was measured at 125 micrometers in length.
What is this?
An egg of Schistosoma haematobium, recognised by its characteristic size (110-170 micrometers in length), internal miracidia and terminal spine. The terminal spine differentiates it from Schistosoma mansoni and Schistosoma japonicum.
Schistosoma haematobium primarily causes genito-urinary schistosomiasis.
The life cycle of schistosomes with the intermediate snail host is represented below and is worthwhile knowing.
What urine collection methodology optimises the chances of finding this pathogen.
A full urine sample taken between 10am and 2pm (when egg deposition into the bladder is supposed to be highest) and after exercise. (Some places advocate a 24 hour urine collection.) Three samples on consecutive days will be more sensitive than one at picking up light infections. The sample should first be examined for both macroscopic and microscopic haematuria. It should then be centrifuged and the sediment examined for eggs. There are methods available for quantifying egg counts, but in my experience this is hardly ever necessary in non-endemic areas for returned travellers.
What are the other laboratory methods that can be used to diagnose the condition caused by this?
- Serology: Does not discriminate between active and past infection. Useful in non-endemic areas for returned travellers.
- Antigen testing and PCR: Will discriminate between active and past infection, but such testing is still largely in a research capacity.
- Mucosal biopsy: Eggs may be identifiable in mucosal biopsy specimens taken from the bladder wall at cystoscopy. Sometimes “ectopic eggs” may be found elsewhere in the body such as in the liver, lungs or spinal cord.
- Full Blood Count: Often demonstrates eosinophilia.
Note that as it can take several weeks for the worm to start producing eggs, both microscopy and serological tests may be negative early on in the infection.
CDC has one of the better web-based resources for schistosomiasis including information on urinary schistosomiasis. Click here to access.