Medycyna Wet. 2006, 62 (3) 278 Praca oryginalna Original paper Praziquantel is a pyrazinoisoquinoline derivative with well-known activity anticestodal and antitrematodal in humans and animals. It was discovered by Bayer AG and Merck in 1972 (1). It is effective at different dose levels according to the target parasite species. In veterinary medicine praziquantel is used at 5 mg/kg in dogs and cats for the elimination of tapeworms by the oral route. Tape- worms in sheep can be very harmful and may cause eco- nomic losses (5, 7, 15, 16). The dosage 3.75 mg/kg was found effective against Moniezia spp. and Thysaniezia spp. while much higher dosage (8-15 mg/kg) is necessary against Avitellina centripunctata and Stilesia globipunc- tata (1-3, 5, 12-15). Anoplocephalid cestodes known from Turkey are to infect sheep Moniezia spp., Thysaniezia spp., Stilesia spp. and Avitellina spp. (4, 16, 18). The mode of action of praziquantel makes the drug different, such as shrinking phenomena were observed in both trematodes and cestodes to praziquantel: Tetanic con- traction of the parasite musculature and rapid vacuolisa- tion of the syncytial tegument (1). This mode of action might cause different excretions form of tapeworms. Spe- cial information about the excretion form of tapeworms after praziquantel treatment is not found in literature. Mansonil-B fi is a tablet formulation of praziquantel (containing 75 mg active ingredient) and it was used for the treatment of sheep. Animal owners reported that no parasite expulsed after drug application and thus the as- sumption was made that their animals died after the treat- ment and they had parasites in their intestines. This study was conducted to evaluate the efficacy of praziquantel using two different dosages on M. expansa and to obser- ve the appearance of tapeworms in the faeces after treat- ment. Material and method For this study, the faeces of 150 Kivircik sheep, a very popu- lar sheep breed specific to Turkey in the Bolu province (North- -West Anatolia/Turkey) were examined for the presence of Mo- niezia expansa microscopically by a flotation and McMaster egg counting method (10). None of the sheep had been pre- viously treated with anthelmintics. Forty-three sheep were positive for Moniezia expansa based on the findings of eggs in the faeces. Thirty-seven animals were selected and housed in- doors. One of the 37 infested sheep was slaughtered in order to assure that the animals were infected with tapeworms. This sheep had a single M. expansa with an approx. volume 25 ml in the small intestine. The weight of the test animals was between 17.7- -35 kg (group 1 mean: 26.34 – 1.09 kg; group 2 mean: 26.61 – 0.91 kg and control group mean: 26.29 – 3.46 kg) and there were 12 female and 24 male sheep. Sheep were allocated into three groups according to the dosage regime as: Group 1  3.75 mg praziquantel/kg b.w., n = 12; Group 2  5 mg prazi- quantel/kg b.w., n = 12; Control group, n = 12. All animals were Field trial of the efficacy of praziquantel for the treatment of monieziosis in naturally infected sheep HAYRETTIN AKKAYA, ABDULKERIM DENIZ*, DENIZ VEREN*, MELTEM ULUTAS ESATGIL Department of Parasitology, Veterinary Faculty, Istanbul University, 34320 Avcilar, Istanbul, Turkey *Bayer-Türk, Animal Health Division. Cakmak Mah. Balkan Cad. No. 53, 34770 Umraniye-Istanbul, Turkey Akkaya H., Deniz A., Veren D., Esatgil M. U. Field trials on the efficacy of praziquantel for treating monieziosis in naturally infected sheep Summary The purpose of the study was to evaluate the efficacy of praziquantel at 3.75 mg/kg b.w. and 5 mg/kg b.w. in treating Moniezia expansa and to observe the appearance of the parasite in the faeces of sheep following the treatment. Thirty-six sheep (24 male + 12 female), naturally infected with Moniezia expansa, were allocated to three groups according to the following dosage regimes: Group 1-3.75 mg/kg b.w., n = 12; Group 2-5 mg/kg b.w., n = 12; Control group, n = 12. The sheep were around 6-7 months old and weighed between 17.7  35 kg. Sheep were randomly divided into equal groups based on mean weight and sex. Faeces were collected after 12, 36, 60, 84, 108, 132 and 156 hours and just before slaughter (final 24 hours faeces) into faecal collection bags in the treatment groups. The collected faeces were then examined macroscopically for any parasite segments and microscopically for parasite eggs. After treatment the sheep excreted parasite segments as either normal parasite forms or deformed forms (melted and capsule or rosary forms). Equal numbers of animals (3 from each group) were slaughtered 10, 11, 12 and 13 days following treatment and their intestinal contents examined for the presence of parasites. None of the treated animals either in group1 or group 2 had strobilae or scolices of M. expansa in their intestine contents after the slaughter. In contrast, sheep in the control group had 0.5-61 ml strobilae and 1-8 scolices belonging to M. expansa, Thysaniezia giardi and Stilesia globipunctata. It was concluded that praziquantel at the dose rates used in the study was 100 % effective against Moniezia expansa. Keywords: praziquantel, Moniezia expansa, anoplocephalid tapeworms, sheep