Impact of praziquantel baiting on intestinal helminths of foxes in southwestern Germany

Fox baits containing 50 mg praziquantel were distributed by aircraft in a 3000 km2 area of southwestern Germany from 1995 to 1999. 20 baits / km2 were initially distributed at intervals of six to twelve weeks. Starting from a prebaiting prevalence of 64 % (95 % C.I. 59–69), a level of 15 % (C.I. 10–21) was reached after 18 months. Further decreasing the frequency and discontinuing the bait distribution caused a surge to 55 % (C.I. 49–61) within 36 months. Other cestode species (Taenia spp., Mesocestoides spp.) showed similar responses, while the prevalence of ascarid nematodes did not decline during baiting. New infections of fox cubs with E. multilocularis, but not with other cestodes, drastically decreased after one year. Prevalences of fox helminths in an external control area remained stable. Our data suggest that repeated praziquantel treatment of free ranging foxes is suitable to reduce the prevalence of E. multilocularis in a large area.