Accurate diagnostics for schistosomiasis: a new role for PCR?

Abstract

When it is important to detect schistosome infection with high sensitivity, particularly where local elimination is planned, detection of parasite-specific DNA should be considered as part of the diagnosis. The process of molecular amplification need no longer be considered to be restricted to sophisticated laboratories, but can be used effectively with modern tools in district hospitals or rural clinics and can be adapted for urine if it is used as the DNA source. With schistosomiasis, observation of a typical egg in urine, stool, or biopsy is taken as evidence of infection; point-of-care (POC) tests based on detecting parasite-specific antigens on a simple matrix have made this simpler and effective particularly in rural settings, but like observation of eggs, these methods are liable to give false negative results and thus miss infected cases. These cases are a likely source of parasite eggs to continue the infection cycle. Thus, although convenient, POC tests are unsatisfactory for epidemiological studies and evaluation of mass treatment campaigns. Methods to detect species-specific DNA fragments in fresh urine or in residue after filtration have been described and shown to be more sensitive and specific than specimen-based, serological, or antigen capture diagnosis. Parasite-specific DNA fragments can also be amplified from blood and stool taken from people infected with any of the major schistosomes. However, the use of urine residue after filtering through filter paper as a source of parasite-specific DNA has greatly simplified the process. Urine can be filtered at the POC using disposable plasticware and then paper dried and placed in a plastic sleeve, which is a simple process. If dry, the product is stable and transport is simple and inexpensive, and DNA can be extracted and amplified in a nearby facility set up for the work. If not POC, this is close to POC and quite feasible and processing by PCR or loop-mediated isothermal amplification process will ensure the universal application of this technology.