Parasites of Horse 3 12:00 - 13:30 Thursday, 22nd July, 2021 Parasites of horse Presentation type Oral 12:00 - 12:15 O-4043 The Atlantic crossing of macrocyclic lactone resistant cyathostomins Martin Nielsen1, Ray Kaplan2 1University of Kentucky, Lexington, USA. 2University of Georgia, Athens, USA Abstract Resistance to the benzimidazole and tetrahydropyrimidine anthelmintic classes is prevalent in equine cyathostomins around the world, but only sparsely and sporadically documented to the macrocyclic lactone (ML) class. In 2020, routine surveillance of anthelmintic efficacy on a farm in Kentucky, USA suggested lack of ML efficacy and available data were analyzed to investigate this further. In 2019, 58 Thoroughbred yearlings were imported from Ireland while another 55 yearlings were born on the US farm. Ivermectin (200 μg/kg) was administered to all yearlings in February 2020, and the FECR was 100% in the US bred yearling groups, but 93.5% (95% credible interval: 85.6-97.6), 70.5% (55.5-99.9), and 74.5% (62.4-83.2) in three groups of the Irish imports. Two of the groups were immediately retreated with ivermectin, yielding FECRs of 33.8% (13.4-61.9) and 23.5% (12.6-45.0), respectively. Horses from these two groups were then assigned randomly to two possible treatments; moxidectin (400 μg/kg) or a triple combination of moxidectin (400 μg/kg), oxibendazole (10 mg/kg), and pyrantel pamoate (6.6 mg/kg). The moxidectin-treated had FECRs of 90.2% (62.6-98.2), 57.3% (26.1-78.6), and 50.0% (30.7-64.2), while the triple combination had a 100% FECR in all treated groups. Subsequently, the efficacy of ivermectin was reassessed in June, 2020 yielding FECRs of 99.8% (99.4-99.9), 87.7% (79.6-93.1), and 62.0% (48.3-72.4) in the three imported groups, while the FECRs of the US bred yearlings all remained in the 99-100% range. This is the first study to demonstrate and confirm ML resistance in cyathostomins through reassessment. ML-resistant cyathostomins were imported from Ireland, which illustrates that the global movement of horses can quickly spread resistant parasite isolates around the world. The equine industry is strongly encouraged to routinely monitor ML efficacy against strongylid parasites, so resistant cyathostomin isolates can be detected and appropriate interventions implemented as early as possible. Presenting author photograph Presenting author biography Dr. Nielsen graduated with his DVM degree from the Royal Veterinary and Agricultural University, Denmark in 2001. He received his Ph.D. in equine parasitology at University of Copenhagen in 2007 and served as assistant professor there until 2011. He then joined the M.H. Gluck Equine Research Center at University of Kentucky where he now serves as Professor and holds the title of Schlaikjer Professor in Equine Infectious Disease. Dr. Nielsen is chair of the AAEP Parasite Control Subcommittee and isco-editor in chief for Veterinary Parasitology. He has published over120 peer-reviewed publications and is co-author of Handbook of Equine Parasite Control. 12:15 - 12:30 O-4044 Incidence of helminth parasites in foals in Ireland receiving interval- based or targeted (selective) anthelmintic treatments Imogen Henderson1, Theo de Waal2, Nicola Walshe2 1Spring Equine Group, Wirksworth, United Kingdom. 2University College Dublin, Dublin, Ireland Abstract A surveillance-based, targeted treatment approach to helminth parasite control is recommended in adult horses, however, susceptibility and morbidity is higher in juveniles. Recent surveys indicate that interval or strategic anthelmintic administration, without faecal worm egg counts (FWEC’s), are frequently employed on studs. This could result in unnecessary treatments, or foals with high parasite burdens remaining undetected. The aims of the study were to monitor the incidence of helminth parasites in foals during their first year via monthly FWEC’s, evaluate changes in anthelmintic treatment regimes, report intervals from treatment to egg detection and describe any potential association between positive FWECs and clinical disease. Results showed that the incidence of Strongyloides westeri in foals <60 days of age increased following the change from interval to targeted (selective) ivermectin treatment but was not associated with clinical disease. The calendar month when ascarid eggs were first detected varied between years. The incidence of Paracaris.spp in foals 90-150 days old was 8.2%, 4.4% and 4.9% in 2018, 2019 and 2020, respectively. In 2019, targeted treatment (fenbendazole) was administered to all foals aged >90 days, from the date of first detection of ascarids on the stud, resulting in a lower incidence (8.8%) in foals aged 151-210 days, compared to 2018 (18.6%), when an interval-based treatment with pyrantel was used and 2020 (16%) when foals aged 90-150 days received a targeted treatment of fenbendazole. Within 7-30 days of receiving ivermectin, 18.8%, 38.9% and 10% of foals had positive FWEC’s for strongyle, S. westeri or ascarid eggs, respectively. Following moxidectin treatment (n=83), positive strongyle egg counts were detected 31-66 days later (median 53 days). Parasites probably contribute little to disease as only 51% of foals receiving veterinary intervention for gastrointestinal or respiratory disease had positive FWEC’s within 1 month compared to 36% of age-matched controls. Presenting author photograph Presenting author biography Jennie graduated from the University of Liverpool in 2002 and worked in stud farm practice and referral hospitals in the UK, Australia and Ireland, undertaking a residency in Equine Internal Medicine at the University of Edinburgh in 2005 and becoming a Diplomat of the ECEIM in 2009. Jennie is currently working as resident vet for an Irish stud farm and her particular interests are neonatology and herd health and biosecurity. 12:30 - 12:45 O-4045 Evaluation of two anthelmintic treatment regimens (strategic vs selective) in donkeys naturally infected by intestinal strongyles Francesco Buono1, Cristina Roncoroni2, Laura Pacifico1, Giovanni Libralato3, Elisa Castaldo1, Diego Piantedosi1, Francesca Mancianti4, Vincenzo Veneziano1 1Department of Veterinary Medicine and Animal Productions, University of Naples Federico II, Napoli, Italy. 2Istituto Zooprofilattico Sperimentale Lazio e Toscana, Rome, Italy. 3Department of Biology University of Naples Federico II, Napoli, Italy. 4Department of Veterinary Science, University of Pisa, Pisa, Italy Abstract Introduction: equine worm programs are based on treatments applied at regular intervals during the year, often without diagnosis. These strategies led to the development of anthelmintic resistance worldwide. To reduce this phenomenon in horses, targeted selective treatments (TST), based on individual Fecal Egg Count (FEC), have been developed, treating only animals with a threshold value>200 eggs per gram (EPG). The present study evaluates during one year two anthelmintic regimes on donkeys naturally infected by intestinal strongyles (Cyathostominae and Strongylus vulgaris) in Italy. Materials and Methods: study animals were allocated in two treatment groups (strategic–ST and selective–TST) of 20 donkeys each, moreover a control group (C-group) of 10 animals were enrolled. Individual FECs were performed monthly using a modified McMaster technique. Results: at the beginning of the study in ST, TST and C-groups the mean EPG were 1585.5, 1627.0 and 1634.4, respectively, no statistical differences were observed (p=0.9815). In August 2015, donkeys belonging to ST and TST were dewormed with fenbendazole drench (7.5 mg/kg) showing a FEC reduction of 99.4% in both groups. All the donkeys of ST group were also treated with FBZ in February and July 2016, while monthly in TST group donkeys with an individual FEC>300EPG were treated. In the ST group after the first and the second treatment the mean EPG follow a progressive increase while remained almost constant in TST group allowing to treat a reduced number of donkeys per time-slot and avoiding high level of infestation (p<0.05). In the ST, TST and C-groups, the mean EPG during the study period was 347.0, 201.0 and 873.7, respectively. Discussion: the study showed that in the TST group the mean EPG of intestinal strongyles was lower than in ST; considering the high prevalence of S. vulgaris, TST in donkeys should be performed with specific parasitological surveillance. Presenting author photograph Presenting author biography Graduated with honors in Veterinary Medicine from the University of Naples in 2011, in the same year he qualified for professional practice. In 2018 he obtained the title of PhD in Veterinary Sciences with a thesis on donkey helminthoses at the University of Naples Federico II. He currently carries out a research grant in equine parasitology on anthelmintic resistance. Veterinary surgeon with particular expertise in internal medicine and gastrointestinal diseases. He is the author of numerous publications in international journals, he has participated as a speaker at national and international conferences. 12:45 - 13:00 O-4046 Autochthonous equine piroplasmosis in Austria Anja Joachim, Esther Dirks, Phebe de Heus, Jessika M.V. Cavalleri, Ilse Schwendenwein, Maria Melchert, Hans- Peter Fuehrer Vetmeduni Vienna, Vienna, Austria Abstract Equine piroplasmosis is caused by Babesia caballi and Theileria equi and transmitted (among other hard ticks) by members of the genus Dermacentor. Infections can lead to life-threatening acute disease with anaemia and organ failure, especially in congenitally