Gasterophilus in horses from Romania: diversity, prevalence, seasonal dynamics, and distribution.

This is the first study that targets the epidemiology of Gasterophilus spp. in slaughtered horses from Romania. Previously to our research, there were five recorded species: Gasterophilus haemorrhoidalis, Gasterophilus inermis, Gasterophilus intestinalis, Gasterophilus nasalis, and Gasterophilus pecorum with a dispersed distribution throughout the country, the data being recorded more than 73 years ago. The collection of Gasterophilus larvae was carried out from the digestive system (stomach, duodenum, and rectum) of horses in three abattoirs, monthly between January 2023 and December 2023. Following dissection, all larvae were stored in absolute ethanol until morphological and molecular identification. The larvae were counted and identified according to morphological keys. Overall, 394 horses were examined, of which 211 (53.6%) were infected with L2 or L3 of Gasterophilus spp. Only two species were found: G. intestinalis (prevalence 52.0%) and G. nasalis (14.0%). Coinfection with both species occurred in 49 horses (12.4%). In total, 9759 larvae were collected (7916 L3 and 1843 L2). Larvae were localized in the stomach (G. intestinalis) and duodenum (G. nasalis) of horses. There was a strong seasonal variation in the mean intensity and mean abundance for both G. intestinalis and G. nasalis larvae and also for coinfections (p < 0.05). There were no significant differences between prevalence and mean intensity across gender, group age, or horse colour. Our findings show that Gasterophilus infection is widespread within Romania territory, being a possible cause of illness and welfare issues in horses.