Wild ruminants as a potential risk factor for transmission of drug resistance in the abomasal nematode Haemonchus contortus

Abstract

Anthelmintic resistance (AR) and gastrointestinal (GI) parasitism are well-known phenomena in domestic ruminants. Wild ruminants, however, pose a potential threat for the spread of AR to sheep and goat farms. We infected three species of wild ruminants, European mouflon (Ovis musimon), roe deer (Capreolus capreolus) and fallow deer (Dama dama), with 8000 third-stage larvae (L3) of the susceptible MHco3 strain and the resistant MHco4 strain of Haemonchus contortus. Infection intensity was highest in mouflons (26,500 ± 150.00 eggs per gramme (EPG) of faeces) on day (D) 58. The roe and fallow deer had low egg counts (50 ± 23.57 to 150 ± 80.64 EPG) to D58, after which no eggs were detected. In vitro egg hatch tests (EHTs) and larval development tests (LDTs) indicated the same level of benzimidazole resistance between mouflons and domestic sheep. Two domestic lambs were then infected with 2500 MHco4 L3 larvae and moved to a clean pasture. Two parasite-free roe deer were introduced to the same pasture 6 weeks later. Infection intensity in the two roe deer was highest on D35, at 800 and 4400 EPG. ED50 from the EHTs, LD50 from the LDTs, and the presence of H. contortus in faecal samples confirmed the transmission of the resistant strain from the wild to the domestic ruminants in the same pasture.