Prevalence of nasopharyngeal myiasis in roe deer (Capreolus capreolus) from an area with high sympatry between wild and domestic ungulates in Central Spain

Infestation by the sheep bot fly Oestrus ovis was firstly reported in a single roe deer from Central Spain in 2022. For assessing the current situation of nasal myiases in this ungulate in this area, the nasopharyngeal cavities of 184 roe deer hunted in Central Spain between January-June 2023 were examined. All larvae were recovered and morphologically identified; in addition, species identification was molecularly confirmed in a subset of specimens. Forty-four roe deer (23.9%; CI 95 17.95–30.74) were positive for different Oestrinae larval stages. Twenty-six animals (14.1%; CI 95 9.44–20.02%) were infested by the roe deer nasal bot fly (Cephenemyia stimulator) with a mean intensity of 35.2 (SD 49.71) larvae/infested animal, and eighteen (9.8%; CI 95 5.90-15.02%) roe deer harboured the sheep bot fly (O. ovis), with a mean intensity of 2.0 (SD 1.33) larvae/infested animal. No mixed infestations by both Oestrinae were found in a single animal. All larval instars (L1, L2 and L3) of both species were identified. Most C. stimulator specimens were located at the nasal turbinates, and a small percentage (3.2%) at the pharynx; all O. ovis larvae were found at the nasal turbinates. Since O. ovis is highly prevalent in sheep and goat flocks from Central Spain, the high sympatry between roe deer and small ruminant populations in the studied area may have increased the risk of cross-infection. Moreover, the finding of mature L3 of O. ovis suggests that this species can complete its life cycle in roe deer. Therefore, monitoring bot flies in sheep and goat flocks as well as in sympatric wild ruminants is strongly recommended for achieving an optimum control of nasal myiases.