Schistosomiasis is an acute and chronic parasitic disease caused by blood flukes of the genus Schistosoma. The Kato-Katz method is the standard recommended by World Health Organization for qualitative and quantitative diagnosis of intestinal schistosomiasis caused by S. japonicum and S. mansoni, because it is highly specific, relatively simple and inexpensive. However, Kato-Katz is less useful in light infections and other available detection methods are neither practical nor sensitive enough for routine or large-scale screening. Thus, improved tests that are also more cost effective are demanded for assessment of infection.
The water buffalo (Bubalus bubalis) is a natural host and reservoir for propagation of Schistosoma. Although it can be infected, the water buffalo does not succumb to schistosomiasis, suggesting a robust immune repertoire. In addition, B. bubalis belongs to Bovidae family like cows (Bos taurus), which have been reported to possess a diverse complementary determining region (CDR) 3 antigen receptor.
In this study, a phage display single-chain Fragment of variation (scFv) library derived from a schistosome-infected water buffalo in China was screened against schistosome antigens, to select antibody that could be used as diagnostic reagent for schistosomiasis. The schistosome antigens, which were highly expressed at various stages of life cycle of the parasite, were initially cloned and over-expressed in vector with maltose-binding protein as solubility tag, purified by immobilized metal affinity chromatography, and subsequently used in biopanning the library. The scFv fragments that bound to the antigens were isolated and characterized. However, when tested against bovine serum albumin, lactoferrin and hemoglobin, the scFvs were also enriched, suggesting non-specificity to the schistosome-antigens.
Our next step is to construct a larger phage display scFv library from the Philippine carabao. Since the Philippine carabao is more exposed to harsher conditions and more parasites, it should offer a diverse immune response and produce potent antibodies. The isolated schistosome-specific scFv will be fused to alkaline phosphatase, which will be used in developing a direct enzyme-linked immune-sorbent assay (ELISA) format diagnosis.