Preparation of Three Fasciola gigantica antigens and determination of their efficacy as a vaccine for protection against fascioliasis in Rabbits

Abstract

This study was included the preparation of vaccine against fascioliasis from three Fasciola gigantica antigens, somatic antigen, excretory-secretory antigen and partially purified cathepsin antigen. Their vaccine efficacy was tested in rabbits, by using 12 Lepus lepus arabica rabbit, aged 2 months, similar weight. The rabbits were subdivided to three groups each of four rabbits and was vaccinated with one antigen emulsified in freund adjuvant. In compare to control groups Which involved 4 rabbits vaccinated with PBS and other four left without vaccination, challenge infection was done by vaccination the animals with 90 metacercaria obtained from experimentally infected intermediate host. All animals were killed 12 weeks after challenge. Protein concentration of all prepared antigens and the molecular weight of P.P.CatA was also measured, which reached (1.5, 1.2 and 0.04) mg/ml in SA, ESA and P.P.CatA respectively, while P.P.CatA 26.7 KD. Protection estimated by followed number of aspects, the first aspect of this study, was the determination the hepatic damage which was evaluated using gross morphometric observations depending upon the severity and intensity of lesions. Significant differences (p<0.05) was noted between vaccinated and control groups. The second aspect was concerned with estimation of fluke number and reduction rate, the high rate (81.3%) recorded in animals vaccinated with P.P.CatA while (39.53%) of those vaccinated with SA. Significant differences (p<0.05) was documented in the length of fluke in animals vaccinated with P.P.CatA. No significant differences were noted in fluke burden (width, length, weight) and fecal egg counts, Significant differences (p<0.01) were noted in egg viability and reduction rate in the vaccinated animals in comparison with control group. ELISA was used for monitoring of IgG levels in all vaccinated and control animals, before and after infection. The IgG increased in the sera of animals vaccinated with SA, ESA and P.P.CatA within 1 week after the first injection. A boosting of the antibody responses was observed in all groups following both the second and third immunization. An increasing in the antibody titers in all vaccinated animals was observed within 2 weeks following challenge. IgG in all vaccinated groups remained high throughout the infection but decreased at approximately 6 weeks after infection, and then remained constant throughout the subsequent weeks. Antibodies to antigens in the sera of the control group increased within the first 2 to 4 weeks after infection but decreased at approximately 8 weeks and then remained constant throughout the subsequent weeks. Accordingly, the results of these aspects could be consider a P.P.CatA as a first best vaccine then secondly ESA.