Time required by different anthelmintics to reach expected efficacy levels in horses infected by strongyles

Abstract

The aim of this study was to determine the time required by different anthelmintic agents to reduce strongyle egg shedding in horses. Fifty horses were divided into five homogenous groups based on faecal egg counts (FECs). Treatment groups received either ivermectin; moxidectin; fenbendazole; piperazine; or no treatment (control group). Faecal examinations were performed 4, 8, 12, 18, 24, 36 and 48h after the anthelmintic treatment. After this period, faecal samples were taken every 24h over the next 12days and finally on alternate days (48-h intervals) for another 14days until the end of the experiment (28days post-treatment). The faecal egg count reduction (FECR) was calculated based on the post-treatment mean FECs in the controls and treated animals. Eggs were absent from the faecal examinations beginning at 72h and 4days, respectively, following treatment with moxidectin or ivermectin. Piperazine showed an FECR greater than 95% from 48h up to 9days post-treatment, with the highest FECR value recorded at 7days post-treatment (98.1%). However, the FECR was lower than 90% in the last two samplings (26 and 28days post-treatment). The febendazole group presented the lowest efficacy with FECR below 90% in all samplings. The faecal cultures showed that at the beginning of the trial, all of the groups presented with mixed infections and were predominantly composed of cyathostomins (92.8%), followed by Strongylus vulgaris (5.6%) and Triodontophorus serratus (1.6%). Only cyathostomin larvae were identified following treatment with fenbendazole or piperazine. In conclusion, horses in the present study had a segment of the cyathostomin population with resistance to fenbendazole and piperazine. The strongyle population was susceptible to macrocyclic lactones, with cessation in egg shedding three and four days after treatment with moxidectin and ivermectin, respectively.

Anthelmintic resistance in equine nematodes: Current status and emerging trends

“…Thus, X means that resistance was tested, but not found, and X-AR means that resistance was tested and found. Country Publication Benzimidazoles Pyrimidines Macrocyclic lactones Algeria Boulkaboul et al (2006) X-AR X Australia Pook et al (2002) X-AR X-AR X Abbas et al (2021) X-AR X-AR Belgium Dorny et al (2000) X-AR X-AR Brazil Toscan et al (2012) X-AR Canever et al (2013) X-AR X-AR X-AR Felippelli et al (2015) X-AR Saes et al (2016) X-AR X Vera et al (2020) X-AR X Flores et al (2020) X-AR X-AR X-AR Martins et al (2021) X-AR X-AR Lignon et al (2021) <...…”

Anthelmintic resistance and novel control options in equine gastrointestinal nematodes

“…This threshold cut-off limit does not seem applicable for determining anthelmintic efficacy in horses, hence, this limit has not been applied in some other studies (Ihler, 1995). The currently available anthelmintic classes show different efficacy levels against cyathostomins (Saes et al ., 2016). Therefore, it was suggested to review these cut-off values particularly for some anthelmintic classes (Coles et al ., 2006).…”

“…Anthelmintic resistance (AR) is generally defined as ‘when a previously effective drug is unable to kill the parasite population while exposed to therapeutic doses (Jabbar et al ., 2006) or loss of sensitivity to a drug in parasitic population that was sensitive to the same drug which is thought to be genetically transmitted (Kohler, 2001)’. AR has been documented in parasites of different animal species including cattle (Lifschitz et al ., 2010; Geurden et al ., 2015), sheep and goats (Coles, 2005; Domke et al ., 2012) and horses (Geurden et al ., 2013; Wolf et al ., 2014; Saes et al ., 2016).…”

Occurrence of Strongylid Nematode Parasites on Horse Farms in Berlin and Brandenburg, Germany, With High Seroprevalence of Strongylus vulgaris Infection

“…Anthelmintic resistance (AR) in equine nematodes is widespread (4,(57)(58)(59). Concerning strongyles it is primarily the BZ drug class against which cyathostomin populations have developed resistance, but also resistance to pyrantel is prevalent (57,(60)(61)(62)(63)(64)(65)(66). Molecular analysis of AR associated genetic changes, for example concerning the respective drug target, promises to allow the detection of AR development at earlier stages than phenotypic tests allow (67).…”