Demonstration of reduced efficacy against cyathostomins without change in species composition after pyrantel embonate treatment in Swedish equine establishments

Consisting of approximately 50 different species, the cyathostomin parasites are ubiquitous in grazing horses. Coinfection with several species is common, and large burdens can cause the fatal disease of larval cyathostominosis. Due to intense anthelmintic drug use, cyathostomin resistance has developed to all available anthelmintic drug groups. Resistance to the anthelmintic drug pyrantel (PYR) has been documented in over 90% of studies published over the past two decades. In Sweden, a study performed in the early 2000s only confirmed resistance in 4.5% of farms. Further, prescription-only administration of equine anthelmintic drugs was enforced in Sweden in 2007. However, it is unknown if this conservative drug use has maintained PYR efficacy in cyathostomins. The aim of the present study was to investigate the effect of PYR on cyathostomin infection in Sweden using fecal egg count reduction tests (FECRTs). Further, the effect of PYR treatment on cyathostomin species composition was studied using metabarcoding. Sixteen farms with at least six horses excreting a minimum of 100 eggs per gram feces were included. Using the current World Association for the Advancement of Veterinary Parasitology (WAAVP) guidelines, PYR resistance was demonstrated in nine of farms, with seven farms showing full susceptibility. Farms with low biosecurity measures had significantly lower efficacy of PYR treatment. The most common cyathostomin species were Cylicocyclus nassatus, Cyathostomum catinatum, Cylicostephanus longibursatus, Cys. calicatus, Cys. goldi, Cys. minutus, Coronocyclus coronatus and Cya. pateratum, accounting for 97% of all sequence reads prior to treatment. Of these, Cyc. nassatus and Cya. catinatum had the highest occurrence, accounting for 68% of all sequence reads prior to PYR treatment. Treatment did not significantly affect the species composition. The results highlight the importance of drug efficacy testing when using PYR to treat cyathostomin infection, even when selective anthelmintic treatment and thus low treatment intensity, is used on the farm

The resistance status of pyrantel in Cyathostominae spp. on Swedish farms

Hästens små strongylider, Cyathostominae spp., är en betesburen grupp endoparasiter som drabbar häst och finns endemiskt över stora delar av världen. Infekterade hästar utvecklar i normalfallet inte några sjukdomssymtom och avmaskning sker för att hålla smittrycket hos betande hästar och på betet lågt, inte för att eliminera smittan helt. Sedan mitten av 1900-talet har en handfull olika anthel-mintika-grupper utvecklats som varit verksamma mot de små strongyliderna. Över tid har dock oaktsamma avmaskningsrutiner lett till resistensutveckling mot bland annat pyrantel och benzimidasoler, och på senare tid även makrocykliska laktoner i vissa länder. I dagsläget används makrocykliska laktoner och pyrantel i störst utsträckning som behandling mot de små strongy-liderna, och det är därför av intresse att övervaka rådande resistensläge med jämna mellanrum. I den här studien analyserades träckprover från 132 hästar med minst 100 ägg per gram (EPG) träck fördelat på 16 gårdar runt om i södra Sverige för att undersöka resistensutvecklingen hos Cyathosto-minae mot pyrantel. I samband med insamling av provmaterial fick gårdsägarna svara på en enkät rörande gårdens hästhållning och rutiner gällande förebyggande åtgärder och avmaskningsrutiner. Träckprover togs i samband med avmaskning med pyrantel och 14 dagar efter avmaskning. Faecal Egg Count (FEC) analyserades med en modifierad McMaster-metod och Faecal Egg Count Resistance Test (FECRT) genomfördes för att analysera resistensläget. Åtta av de 16 medverkande gårdarna uppvisade en resistent strongylidpopulation. Resultatet tyder på att resistensutvecklingen har fortskridit sedan den senast kontrollerades 2007, trots reglerad användning av anthelmintika sedan dess. Det sågs inga statistiska samband mellan EPG före avmaskning och ålder, eller EPG innan avmaskning och hur ofta gårdarna mockade sina hagar. Det sågs däremot en koppling mellan användandet av separata sommar- och vinterhagar och effekten av pyrantel, de gårdar som applicerade användande av separata sommar- och vinterhagar hade en statistiskt signifikant högre effekt än de gårdar som använde samma hagar året om.The horse's small strongyles, Cyathostominae spp., are a pasture-borne group of endoparasites that affect horses and are endemic over large parts of the world. Infected horses do not normally develop any symptoms of disease and deworming is done to keep the infection in grazing horses and on the pasture low, not to eliminate the infection completely. Since the middle of the 20th century, different anthelmintic groups effective against small strongyles have been developed. Over time, however, negligent use of anthelmintics has led to the development of resistance to, among other things, pyrantel and benzimidazoles, and more recently also macrocyclic lactones in some countries. Currently, macrocyclic lactones and pyrantel are the main drugs used as treatment against the small strongyles in horses, and it is therefore of interest to monitor the prevailing resistance for the two anthelmintics. In this study, faecal samples from 132 horses with at least 100 Eggs Per Gram (EPG) faeces distributed over 16 farms around southern Sweden were analyzed to investigate the development of resistance to pyrantel in Cyathostominae spp. The farm owners also answered a questionnaire concerning the farm's horse management and routines regarding preventive measures and deworming routines. Faecal samples were collected the same day as deworming and 14 days after deworming. Faecal Egg Count (FEC) was performed on the stool samples in the form of a modified McMaster method. Faecal Egg Count Resistance Test (FECRT) was performed to analyze the resistance status of the farms. Eight of the 16 participating farms showed a resistant strongyle population. The result indicates that the development of resistance in Sweden has progressed since it was last checked in 2007, despite regulated use of anthelmintics since then. No connection was seen between EPG before deworming and age, or EPG before deworming and how often the farms cleaned their paddocks of manure. There was a connection between the use of separate pastures depending on season and a lower risk of anthelmintic resistance

Demonstration of reduced efficacy against cyathostomins without change in species composition after pyrantel embonate treatment in Swedish equine establishments

Consisting of approximately 50 different species, the cyathostomin parasites are ubiquitous in grazing horses. Co-infection with several species is common, and large burdens can cause the fatal disease of larval cyathostominosis. Due to intense anthelmintic drug use, cyathostomin resistance has developed to all available anthelmintic drug groups. Resistance to the anthelmintic drug pyrantel (PYR) has been documented in over 90% of studies published over the past two decades. In Sweden, a study performed in the early 2000s only confirmed resistance in 4.5% of farms. Further, prescription-only administration of equine anthelmintic drugs was enforced in Sweden in 2007. However, it is unknown if this conservative drug use has maintained PYR efficacy in cyathostomins. The aim of the present study was to investigate the effect of PYR on cyathostomin infection in Sweden using fecal egg count reduction tests (FECRTs). Further, the effect of PYR treatment on cyathostomin species composition was studied using metabarcoding.Sixteen farms with at least six horses excreting a minimum of 100 eggs per gram feces were included. Using the current World Association for the Advancement of Veterinary Parasitology (WAAVP) guidelines, PYR resistance was demonstrated in nine of farms, with seven farms showing full susceptibility. Farms with low biosecurity measures had significantly lower efficacy of PYR treatment. The most common cyathostomin species were Cylicocyclus nassatus, Cyathostomum catinatum, Cylicostephanus longibursatus, Cys. calicatus, Cys. goldi, Cys. minutus, Coronocyclus coronatus and Cya. pateratum, accounting for 97% of all sequence reads prior to treatment. Of these, Cyc. nassatus and Cya. catinatum had the highest occurrence, accounting for 68% of all sequence reads prior to PYR treatment. Treatment did not significantly affect the species composition. The results highlight the importance of drug efficacy testing when using PYR to treat cyathostomin infection, even when selective anthelmintic treatment and thus low treatment intensity, is used on the farm