The effect of Fasciola hepatica infection on respiratory vaccine responsiveness in calves

Fasciola hepatica is a common parasite in cattle, and bovine fasciolosis causes significant production losses, as well as being a zoonotic disease of global importance. F. hepatica has been shown to have immunoregulatory effects and the aim of this research was to establish whether F. hepatica infection influences the response to vaccination against respiratory pathogens in calves. A total of 48 calves were randomly and equally allocated to two groups. The experimental group was infected with F. hepatica, while the other group was used as a control. At week 2 and 6 after infection calves from both groups were administered a vaccine containing inactivated PI-3, BRSV and Mannheimia haemolytica, pathogens commonly associated with bovine respiratory disease. Blood samples were taken weekly over 12 weeks to measure specific antibodies against all vaccine antigens and against F. hepatica, as well as IgG1 and IgG2 isotypes for PI-3 and BRSV specific antibodies. Faecal samples were examined for F. hepatica eggs and routine haematology and liver enzyme biochemistry were performed and cytokine production in vitro measured. Liver enzymes (GGT and GLDH) and eosinophils were significantly higher in the experimental group, whereas neutrophil numbers were higher in the control group. There was no significant difference between the groups in terms of vaccine-specific total responses to PI-3, BRSV and M. haemolytica. IgG1 levels were higher in comparison to IgG2 levels in both PI-3 and BRSV specific antibodies. IL-4 levels from stimulated and unstimulated PBMC were significantly higher in the control group. IFN-γ levels were significantly higher in PBMC from the control group when cultured in medium only. No significant differences were noted in the levels of other cytokines measured. In this work, no effect of early F. hepatica infection on the antibody responses to a range of respiratory vaccine antigens in calves was shown. However, differences in cytokine responsiveness of PBMC between control and infected groups were observed, indicating that further work in measuring the effect of F. hepatica infection response to challenge infection following vaccination would be warranted.