The Use of Innovative Diagnostics to Inform Sustainable Control of Equine Helminth Infections

Changes in equine strongylid communities after two decades of annual anthelmintic treatments at the farm level

The aim of this study was to assess the changes in strongylid communities of domestic horses after two decades of regular anthelmintic treatments; the changes in prevalence and relative abundance of individual strongylid species and their contribution to the observed alterations were estimated. The study was conducted in 2023; data collected in 2004 were used for comparison; 39 horses from two farms in Ukraine (22 horses in 2004 and 17 in 2023) were examined. In total, 18,999 strongylid specimens were collected by in vivo diagnostic deworming method before (in 2004, 9119 specimens) and after (in 2023, 9880 specimens) frequent application of anthelmintics. Strongylids were identified morphologically. Thirteen strongylid species were found in horses in 2023; only small strongylids (Cyathostominae) were recorded. In 2004, 21 species were found: 6 species of large strongylids (Strongylinae) and 15 of cyathostomins. Species richness (Margalef's index) and species diversity (Shannon's and Simpson's indexes) decreased over two decades on both farms; the Berger-Parker dominance index for C. nassatus dramatically increased up to 74.4. The dissimilarity of strongylid communities of 2023 and 2004 was primarily connected with the disappearance of large strongylids and rare cyathostomin species after two decades of regular anthelmintic treatments. SIMPER analysis revealed that C. nassatus and C. catinatum mostly contributed to this dissimilarity. A trend of gradual transformation of the strongylid community structure from multimodal (in 2004) to bimodal (in 2023) was observed on both farms.

Understanding temporal and spatial distribution of intestinal nematodes of horses using faecal egg counts and DNA metabarcoding

This study reports the spatial and temporal distribution of ascarid and strongylid nematodes in Thoroughbred horses by age category across different climatic zones in Australia over an 18-month period. Faecal samples (n = 2046) from individual horses were analysed using the modified McMaster technique for faecal egg counts (FECs). Strongylids were identified using PCR-directed next-generation sequencing of the second internal transcribed spacer (ITS-2) of the nuclear ribosomal DNA. Yearlings had the highest prevalence (82%) of strongyle eggs followed by weanlings (79%), foals (58%), wet mares (49%) and dry mares (46%). For Parascaris spp., foals had the highest prevalence (35%) followed by weanlings (21%) and yearlings (10%). The highest mean FECs for Parascaris spp. were observed in foals (525 eggs per gram [EPG] of faeces) while those for strongyles were in yearlings (962 EPG). Among horses that were classified as adults at the time of sampling, 77% (860 of 1119) of mares were low (i.e., <250 EPG) strongyle egg-shedders. Mean strongyle FEC counts were highest in the Mediterranean (818 EPG) followed by summer (599 EPG), winter (442 EPG), and non-seasonal (413 EPG) rainfall zones. Twenty-six nematode species were detected, with Cylicostephanus longibursatus (26.5%), Cylicocyclus nassatus (23.7%) and Coronocyclus coronatus (20.5%) being the most frequently detected species. Their richness and relative abundance varied with horse age, season and climatic zone. In addition, Strongylus equinus and Triodontophorus spp. (T. brevicauda and T. serratus) were also detected. This comprehensive study elucidates spatial (climatic zone) and temporal (i.e., seasonal) trends in prevalence and burdens of intestinal nematodes in Australian horses using non-invasive conventional and molecular methods. The information presented in this study is crucial for developing integrated management strategies to control horse parasites in farmed horses.