First report of multiple drug resistance in trichostrongyles affecting sheep under field conditions in Italy.

Drug resistance in sheep gastrointestinal trichostrongyles is a cosmopolitan major constraint to small ruminant production. Despite reports that anthelmintic drug resistance has become common, there are limited information on the presence of drug resistance in Italy. The purpose of this study was to determine the effect of four anthelmintics to control infection in sheep in central Italy. Fifty sheep with fecal egg counts (FEC) > or =150 eggs per gram were selected on each of three farms (n = 150 total sheep) which were randomly allocated to one of five groups. Groups were treated with febantel, levamisole, ivermectin, or moxidectin while the fifth group acted as the control group. A FEC reduction test (FECRT) was conducted on each animal and the mean FEC of each treatment group was compared to that of the control group within farm. Resistance was declared when percentage reduction (R) <95% and the lower 95% confidence interval was <90%. Levamisole (mean R = 89%) resistance was found on all farms and ivermectin (mean R = 93%) resistance was found on two of the three farms. Posttreatment larval cultures showed the presence of Teladorsagia (Ostertagia) circumcincta and Trichostrongylus spp. larvae. Febantel (mean R = 96%) and moxidectin (mean R = 100%) remained effective. This study suggests that drug resistance in sheep gastrointestinal trichostrongyles is present in central Italy and a potential problem which would justify a broader nationwide geographical investigation.