Fasciola hepatica: antibody levels in sheep serum before and after treatment with anthelmintic

Abstract

Two groups of sheep were treated with the anthelmintic diamphenithide three and six weeks respectively after oral infection with metacercariae of Fasciola hepatica. A third group was infected but left untreated. The levels of circulating antibody against three parasite antigens Tl (juvenile tegument glycocalyx). T2 (adult tegument) and G (gut secretions) were monitored throughout infection and recovery-periods using an indirect fluorescent antibody technique with serial sections of plastic-embedded fluke tissues as test antigen. Termination of infection after three weeks prevented the development of the T2 antibody response and led to significant premature peaking and, or, decline of Tl and G antibodies. However the magnitude of these peaks was unaffected by chemotherapy. Treatment six weeks after infection had no significant effect on the Tl or G antibody titres and these antibody profiles closely resembled the equivalents in control animals. However the T2 antibody response was somewhat reduced, supporting the view that while T2 granules occur in the tegumental syncytium from an early stage in fluke development the T2 antigens are not expressed at the surface until late in the liver migration phase. In the three week and six week treated groups, decline from peak antibody titres during the recovery period paralleled natural decline in antibody titres after bile duct invasion in the untreated control animals. This provides evidence for immunological isolation of the bile duct habitat.