INVESTIGADORES
FERNANDEZ Alicia Silvina
congresos y reuniones científicas
Título:
A survey on anthelmintic resistance in grazing cattle of Argentina
Autor/es:
FIEL, CÉSAR; CRISTEL, SILVINA; ANZIANI, OSCAR; DESCARGA, CARLOS; CETRÁ, BIBIANA; ROMERO, JORGE; FERNÁNDEZ, ALICIA SILVINA; ENTROCASSO, CARLOS; LLOBERAS, MERCEDES; STEFFAN, PEDRO
Lugar:
Liverpool
Reunión:
Conferencia; 25th International Conference of the World Association for the Advancement of Veterinary Parasitology; 2015
Institución organizadora:
University of Liverpool
Resumen:
Anthelmintic resistance (AR) in nematodes parasiting domestic ruminants is an increasing phenomenon over the world. A large scale field study was carried out to assess the current situation in cattle of Argentina. Thirty-one beef farms from the central and northeastern areas of Argentina were selected, in which beef production was based on pasture grazing and the use of different drugs at several times to control trichostrongyle infections. Faecal egg count reduction tests (FECRT) were performed to determine the clinical efficacy of ivermectin (IVM 1%, 0.2 mg/kbw), ricobendazole (RBZ 15%, sc, 3.75 mg/kbw) and levamisole (LVM, Phosphate 18.8%, sc, 7.5 mg/kbw). Weaned calves of 7-10 months old, weighing 180 kg in average, which had not been dewormed for at least 60 days before the survey, were distributed into 4 comparable groups of 15 animals each according to individual nematode eggs counts (epg), and assigned to one of the treatments as above and an untreated control group. Faecal samples were taken at treatment (day 0) and at day 14. Coprocultures to establish the proportional contribution ofeach species to worm infection were also performed. Efficacy of each drug was determined by comparing the mean epg of each group at day 0 and day 14. Resistance was established when FECRT revealed an efficacy < 90%. To establish the drug classes and frequency of use through the years a basic questionnaire was completed by farmers. Results show that 93.5% of the farms presented AR to any of the drug classes. Resistance to IVM was present in 28 farms (90.3%), mean efficacy of 60.9% (range 0-88.5%). Resistance to RBZ was diagnosed in 9 farms(29%), mean efficacy of 69.9% (range 13.9-88.1%). Multiple-resistance to IVM and RBZ was detected in 8 farms (25.8%). Resistance to LVM was not found in any farm, its mean efficacy was 97.7% (range 90.9-100%). Mainly Cooperia spp. but also Haemonchus spp. and Trichostrongylus spp. were the genera identified in those farms with resistance to IVM. Cooperia spp. was predominant in the farms with resistance to RBZ but also Ostertagia spp. and Haemonchus spp. in lower proportions. The high levels of resistance to IVM are in consonance with its intensive use in the last two decades. The increasing resistance to benzimidazoles and the multiple-resistance to IVM and RBZ should be also noticed. The relatively scarce use of LVM may account for its high efficacy in this study.