Culicoides biting midges (Diptera: Ceratopogonidae) feeding on donkeys in the United Kingdom, with reference to the risk of transmission and persistence of African horse sickness virus

Abstract

African horse sickness virus (AHSV: Sedoreoviridae; Orbivirus) causes a severe and often fatal disease in horses (African horse sickness: AHS) and is transmitted almost exclusively by Culicoides biting midges (Diptera: Ceratopogonidae). In recent years, unprecedented outbreaks of AHSV have occurred in new geographical foci in Thailand and other related Culicoides-borne viruses continue to emerge unexpectedly, causing disease outbreaks in northern Europe. This study investigated Culicoides abundance and diversity at a donkey (Equus asinus) sanctuary in southern England. The incidence and severity of AHS in infected donkeys are lower than in horses, with concerns, therefore, that these species could act as potential reservoirs in the event of an incursion of AHSV. A total of 21,350 Culicoides of 20 species were collected over 14 nights during spring and summer 2019 using three Onderstepoort Veterinary Institute ultraviolet light-suction traps. The most abundant species were identified within the subgenus Avaritia (19,574; 91.7%), which are known vectors of other Orbiviruses in northern Europe and have been previously identified as putative vectors of AHSV in southern Europe. Furthermore, Culicoides blood-feeding on donkeys was confirmed for the subgenus Avaritia through polymerase chain reaction of blood-fed female Culicoides using a 685 bp region of the cytochrome c oxidase subunit 1 gene. Data on the size and distribution of the donkey population and the potential impact of infection with AHSV on donkeys within the United Kingdom are scarce. This study demonstrates that large populations of Culicoides can exist near these hosts and that they regularly take blood meals from them. There is a potential risk that donkeys could play a significant role in transmission and persistence of AHSV in the event of an incursion into the United Kingdom, which could complicate disease control.