Laboratory transmission potential of British mosquitoes for equine arboviruses

Background: There has been no evidence of transmission of mosquito-borne arboviruses of equine or human health

concern to date in the UK. However, in recent years there have been a number of outbreaks of viral diseases spread by

vectors in Europe. These events, in conjunction with increasing rates of globalisation and climate change, have led to

concern over the future risk of mosquito-borne viral disease outbreaks in northern Europe and have highlighted the

importance of being prepared for potential disease outbreaks. Here we assess several UK mosquito species for their

potential to transmit arboviruses important for both equine and human health, as measured by the presence of viral

RNA in saliva at diferent time points after taking an infective blood meal.

Results: The following wild-caught British mosquitoes were evaluated for their potential as vectors of zoonotic

equine arboviruses: Ochlerotatus detritus for Venezuelan equine encephalitis virus (VEEV) and Ross River virus (RRV),

and Culiseta annulata and Culex pipiens for Japanese encephalitis virus (JEV). Production of RNA in saliva was demonstrated at varying efciencies for all mosquito-virus pairs. Ochlerotatus detritus was more permissive for production

of RRV RNA in saliva than VEEV RNA. For RRV, 27.3% of mosquitoes expectorated viral RNA at 7 days post-infection

when incubated at 21 °C and 50% at 24 °C. Strikingly, 72% of Cx. pipiens produced JEV RNA in saliva after 21 days at 18

°C. For some mosquito-virus pairs, infection and salivary RNA titres reduced over time, suggesting unstable infection

dynamics.

Conclusions: This study adds to the number of Palaearctic mosquito species that demonstrate expectoration of viral

RNA, for arboviruses of importance to human and equine health. This work adds to evidence that native mosquito

species should be investigated further for their potential to vector zoonotic mosquito-borne arboviral disease of

equines in northern Europe. The evidence that Cx. pipiens is potentially an efcient laboratory vector of JEV at temperatures as low as 18 °C warrants further investigation, as this mosquito is abundant in cooler regions of Europe and

is considered an important vector for West Nile Virus, which has a comparable transmission ecology