Comparison of the vaccine efficacy of gamma-irradiated Schistosoma japonicum cercariae with the defined antigen Sj62(IrV-5) in pigs

Development of a vaccine against Schistosoma japonicum which can protect bo th man and the domestic animal zoonotic reservoirs of infection would be an invaluable tool in attempts to control this infection in those areas in wh ich conventional control methods have failed to break transmission. The pig is a natural host of S. japonicum and because of its anatomical and immuno logical similarities to humans, it is a potentially valuable host for studi es on S. japonicum in particular and schistosomes in general. Radiation-att enuated cercariae are highly effective in inducing immunity in experimental schistosomosis and there are promising reports of partial protection again st schistosomes with recombinant-derived individual antigens. In the presen t stud, we have set out to establish a protocol for inducing protection wit h gamma cercariae in pigs and to assess the protective capacity of recombin ant and naked DNA formulations of Sj62, a 62 kDa region of S. Japonicum myo sin. The corresponding S. mansoni version or Sj62, recombinant IrV-5, has p reviously been implicated in irradiated vaccine immunity in S. mansoni infe ctions and has been shown to induce high levels of immunity in a variety of hosts. Groups of pigs were immunised three times at 2-week intervals with 2000 cer cariae irradiated at 20 krad, with Sj62 as a recombinant (rSj62) incorporat ed in Freund's adjuvant, a micellar preparation, or as a naked DNA construc t. Vaccination with irradiated cercariae did not induce significant anti-Sj 62 antibody but following intramuscular challenge with 2000 cercariae, the vaccinated pigs showed >95% resistance as assessed by reduced faecal egg ou tput, worm tissue egg burdens and also reduced septal fibrosis. Immunisatio n with each of the Sj62 formulations induced significant anti-Sj62 antibody responses, the highest titre (>12,800) being with the Freund's preparation but none of the Sj62-immunised groups showed significant resistance to cha llenge. The data suggest that Sj62 shows little promise as a vaccine candid ate for schistosomosis. (C) 2001 Elsevier Science B.V. All rights reserved.