Abstract
Liver flukes (Fasciola spp., Opisthorchis spp., Clonorchis sinensis) and blood flukes (Schistosoma spp.) are parasitic helminths causing neglected tropical diseases that result in substantial morbidity afflicting millions globally. Affecting the world’s poorest people, fasciolosis, opisthorchiasis, clonorchiasis and schistosomiasis cause severe disability; hinder growth, productivity and cognitive development; and can end in death. Children are often disproportionately affected. F. hepatica and F. gigantica are also the most important trematode flukes parasitising ruminants and cause substantial economic losses annually. Mass drug administration (MDA) programs for the control of these liver and blood fluke infections are in place in a number of countries but treatment coverage is often low, re-infection rates are high and drug compliance and effectiveness can vary. Furthermore, the spectre of drug resistance is ever-present, so MDA is not effective or sustainable long term. Vaccination would provide an invaluable tool to achieve lasting control leading to elimination. This review summarises the status currently of vaccine development, identifies some of the major scientific targets for progression and briefly discusses future innovations that may provide effective protective immunity against these helminth parasites and the diseases they cause.
Highlights
This article provides an overview of recent progress in the development of vaccines against digenetic trematodes which parasitise the liver (Fasciola hepatica, F. gigantica, Opisthorchis spp., Clonorchis spp.) and blood system (Schistosoma spp.) and are the cause of important but neglected tropical diseases affecting millions
Genetic analysis of several vaccine candidates (FhCL1, FhCL2, FhPrx, FhLAP and FhHDM (F. hepatica helminth defence molecule [8])) showed that F. hepatica exhibits only a low level of allelic variability in the sequences encoding each of these proteins amongst isolates from different geographical regions; this suggests the variability reported among vaccine studies are not related to heterogeneity in these genes, thereby reinforcing the idea that they would be suitable immunogens against liver fluke parasites globally [15]
Adaptive and innate immune responses are stimulated by excretory/secretory (ES) products released by the liver fluke and by the resulting tissue damage; there appears to be only partial protection conferred in the hamster experimental model of opisthorchiasis and in humans; this may possibly be due to immune evasion mechanisms of the parasite, immune suppression, the worm tegument able to withstand immune attack and/or the location of the parasite within the bile ducts [37]
Summary
This article provides an overview of recent progress in the development of vaccines against digenetic trematodes which parasitise the liver (Fasciola hepatica, F. gigantica, Opisthorchis spp., Clonorchis spp.) and blood system (Schistosoma spp.) and are the cause of important but neglected tropical diseases affecting millions. F. hepatica and F. gigantica are important parasites of domesticated animals, greatly affecting the economy of the agricultural community worldwide [1]. Because of their relatedness and life cycle similarities [1], there is a clear parallel in the approaches taken towards vaccine development (e.g., methods used in the identification of candidate antigens, the technology applied to produce vaccines and their testing in mammalian hosts) for each of these fluke species. Current progress and recent innovations that may deliver vaccines against these parasites in the future are considered and emphasised It is a sobering and sad reality that, notwithstanding the considerable efforts undertaken, and despite encouraging developments recently in some areas, no licensed products are available currently for the prevention of any of the infections caused by these parasitic worms.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
