Potential vectors of equine arboviruses in the UK

Abstract

There is growing concern about the increasing risk of disease outbreaks caused by arthropod-borne viruses (arboviruses) in both human beings and animals. There are several mosquito-borne viral diseases that cause varying levels of morbidity and mortality in horses and that can have substantial welfare and economic ramifications. While none has been recorded in the UK, vector species for some of these viruses are present, suggesting that UK equines may be at risk. The authors undertook, therefore, the first study of mosquito species on equine premises in the UK. Mosquito magnet traps and red-box traps were used to sample adults, and larvae were collected from water sources such as tyres, buckets, ditches and pools. Several species that are known to be capable of transmitting important equine infectious arboviruses were trapped. The most abundant, with a maximum catch of 173 in 72 hours, was Ochlerotatus detritus, a competent vector of some flaviviruses; the highest densities were found near saltmarsh habitats. The most widespread species, recorded at >75 per cent of sites, was Culiseta annulata. This study demonstrates that potential mosquito vectors of arboviruses, including those known to be capable of infecting horses, are present and may be abundant on equine premises in the UK.

Laboratory transmission potential of British mosquitoes for equine arboviruses

“…Here, we focus on the mosquito species used in this study in relation to the ecological attributes which make them of interest as candidate vectors for the viruses tested. Ochlerotatus detritus is considered the primary species associated with brackish water that causes biting nuisance for humans in the UK [66,67] and was trapped on seven of nine saltmarsh associated equine premises in the UK in a recent study [68]. Natural exposure of horses to Oc.…”

“…Culiseta annulata has been shown to bite horses and other large animals in the UK [65,68,70] and engorged females have also been captured in horse baited traps in France and Switzerland [61,71]. This species was found on 75% (24/32) equine premises sampled in a previous study in the UK [68]. Biting nuisance was experienced on two such premises during sampling, which was strongly suspected to be related to poorly drained muck-heaps which contained high densities of larvae identified as Cs.…”

“…The equine arboviruses generally have complex enzootic transmission cycles involving wildlife as reservoir hosts and 'bridge vectors' with broad feeding preferences which can carry virus from the reservoir host to other hosts; including humans and horses, both of which are clinically affected. The three viruses investigated in the present study (VEEV, RRV, JEV) have significant impacts on the health of people and horses (summarised in [15]) in endemic areas. Venezuelan equine encephalitis virus circulates in enzootic cycles between rodent hosts and mosquito vectors in Mexico, Central and South America [16] and has a complex transmission cycle involving regular mutation of the virus, facilitating transmission to humans and horses through broadening of the vector and host ranges.…”

“…This results in an epizootic cycle during which, virus amplification in the horse is sufficient to result in mosquito infection and this is thought to significantly increase the risk of human infection [17]. VEEV infection causes neurological signs in humans and horses and significant infection and mortality rates in horses [15,18].…”

The challenges posed by equine arboviruses

“…Equine morbidity and mortality information for mosquito-borne viruses affecting horses is presented in Chapman et al [6]. Inapparent infections with limited clinical signs (e.g.…”