Current status and future prospects for a vaccine against schistosomiasis

Abstract

Schistosomiasis remains an intractable problem in many parts of the world. Whereas the schistosome parasites cause little in the way of disease, their eggs become trapped in tissues of the host and elicit powerful and potentially damaging immune responses that are responsible for the pathology. Despite nearly four decades of effort there is still no effective vaccine against schistosomiasis, although a single vaccine candidate is undergoing clinical trials at present. Animal models have revealed much about disease progression and pathology. However, problems remain in identifying appropriate protective antigens to elicit immune responses that will attack the parasite but will not cross-react with egg antigens and thus increase the chance of developing severe chronic disease in individuals that have already been infected. This review summarizes the life-cycle of the parasite, current knowledge of pathogenesis and acquired immunity based on animal studies and observations in humans and the status of efforts in the vaccine development field.

Schistosomiasis vaccines

“…There are several reasons for this cautious approach. For example, Lebens et al 18 have pointed out, and we concur, that some of the proposed vaccination strategies based on studies performed only in the mouse model could have undesirable effects in some individuals if taken to human clinical trials.…”

Current Status of Vaccines for Schistosomiasis

“…Below, we review the most recent and pertinent data on the major vaccine antigens for schistosomiasis; some have been the focus of attention for many years, while others are newly described but show particular promise. Table 1 summarizes the data for some of the most promising S. mansoni vaccine antigens discovered in the last 10 years, as well as those that were independently tested under the umbrella of the TDR/WHO committee in the mid-1990s (8); the latter group has been reviewed extensively elsewhere (26,87,115).…”

Comparative modeling of thioredoxin glutathione reductase from Schistosoma mansoni: A multifunctional target for antischistosomal therapy

“…Currently available drugs include praziquantel (effective in the treatment of all forms of disease), oxamniquine (for intestinal type caused by S. mansoni) and metrifonate (for urinary schistosomiasis) [1]. Since the chemotherapy is limited, temporary and prone to resistance, development of vaccines is a challenging alternative [2]. Sequencing of the parasite genomes, manipulating gene expression and understanding gene function, promise faster identification of targets for diagnostics, drugs and vaccines [3].…”