New opportunity for the control of schistosomosis japonica: Exploring heteroogous antigens in Philippine Fasciola for diagnosis and vaccination

Professorial Chair Lecture

Professional Chair in Veterinary Public Health

Place

Philippine Veterinary Medical School, USA

Date

2004

Abstract

This paper gives an overview of Schistosomosis japonica as an important public health problem in the Philippines, describes its epidemiology and control, and reviews studies that point to cross reactivity and cross resistance between Fasciola hepatica and Schistosoma mansoni in animal models. A study conducted by this author was also presented exploring the antigens of Philippine F. gigantica in immunodiagnosis of schistosomosis and in investigating the cross-resistance between carabaos and mice. Schistosomosis japonica continues to be a serious problem in endemic communities in the country, with reports of 6.6% to as high as 45% prevalence in some places. Human infection is partly due to animals serving as reservoirs of infection. The chief control strategy is chemotherapy and praziquantel following a diagnosis of infection. For diagnosis, fecalysis and circumoval precipitin test (COPT) are used but have the disadvantages of low sensitivty and the occurrence of false positives, respectively. Moreover, the COPT requires obtaining large quantities of schistosome egg antigens from laboratory-infected animals, which is costly. Praziquantel resistance is inevitable. Hence, there is a need for new antigens for immunodiagnosis and vaccinations of schistososmosis in humans. Reports of cross-reactivity and heterologous resistance with F. Hepatica has encouraged this author towards these aspects of research. The first study demonstrated cross-reactivity of F. gigantica crude extracts with A. Japonicum in an ELISA cross-reactive F. gigantica crude somantic antifens (FgSom) recognized by anti-S. Japonicum sensitized mice and rabbits were identified by Western blotting in the range of <14 kDa to 66 kDa. The second study used the FgSom in an ELISA to diagnose carabao schistosomosis. While it was not feasible for diagnosis of carabao infection due to the high false positive rate (75%), FgSom shows promise for detection of antibodies to S. japonicum in humans, as there has been no report of human fasciolosis in the country. Heterologous resistance was studied in 337 carabao residents in endemic Leyte and in mice immunized with FgSom. Evidence for heterologous resistance in carabaos was the low schistosome infection prevalence (2.1% vs. 94.6%) and decreased pattern of age-specific prevalence in schistosomosis-infected animals as opposed to the increasing trend in Fasciola-infected carabaos; concurrent infection with fasciolosis; the low ELISA titers to S. Japonicum adult worm antigen but high antibody titers to FgSom in infected animals and the presence of several common antigens as revealed by Western blotting. Further evidence was sought in BALB/c mice immunized with FgSom, which had a lowered mean worm recovery (3.4 worms vs. 5 worms) and proportion with liver granoloma (64% vs. 90%) when challenged with S. Japonicum cercariae 45 days after immunization, compared to npn-immunized but S. Japonicum-infected mice. The protection schistosome vaccine antigens are similar to homologous antigens. This could be attributable to the low immunization dose and possibly to the immunization schedule used. Further studies are needed to explore the use of crude extracts and egg antigens of F. gigantica for use in diagnosis of human schistosome infections and to perform immunization experiments in animals, the time using a higher immunization dose, different route of immunization, and longer immunization schedule.

This document is currently not available here.

Share

COinS