Scientists at The Pirbright Institute have used genetic analysis and wind modelling to show that the 2016 bluetongue outbreak in Cyprus was caused by bluetongue virus serotype 8 (BTV-8). The virus most likely crossed over to Cyprus in midges blown from the coastal regions of Syria, Lebanon or Israel.
Bluetongue is a non-contagious disease of ruminants such as sheep, cattle and goats that is spread between animals by Culicoides biting midges. The disease is caused by bluetongue virus (BTV), of which there are at least 29 known serotypes.
In September 2016, suspected cases of bluetongue in sheep were simultaneously reported in three diﬀerent locations in Cyprus. Scientists at the European Union Reference Laboratory for Bluetongue (EURL-BT) at The Pirbright Institute confirmed that BTV-8 was present in all samples submitted by the National Reference Laboratory in Nicosia, Cyprus. This was the first time that this strain had caused cases in Cyprus, although BTV-3, -4 and -16 have caused several outbreaks on the island since 1924.
In a study published in the journal Viruses, scientists in the Non-Vesicular Reference Laboratory (NVRL) at Pirbright analysed the entire genomes of five isolates and found that the BTV-8 causing outbreaks in Cyprus is different to the BTV-8 strain currently circulating in Europe. The genetic analysis showed that several genetic segments in the Cyprus strain had likely come from other Israeli strains through a process known as reassortment, where different viruses can swap genetic segments if they infect the same animal simultaneously.
The team next investigated how this BTV-8 strain may have arrived in Cyprus. The possibility that the virus was imported through animal movement was low because the first bluetongue cases occurred in three different locations in Cyprus that were not linked to each other through animal transport. As the midges that carry bluetongue can be dispersed to different areas on the wind the researchers examined weather events in the days and weeks prior to the notification of the cases.
Using historical meteorological data and wind modelling, collaborating scientists at the Met Office were able to show that weather conditions in the Mediterranean could have been responsible for midges carrying the virus to travel into Larnaca, Cyprus from the mainland coastlines of Lebanon, Syria or Israel between August and September 2016. There are multiple BTV types circulating in these countries, which would provide the right conditions for reassortment between strains. This aligns with the findings from the team’s genetic analysis, showing that the Cyprus BTV-8 strain is likely to have originated in these countries rather than Europe, where a single BTV-8 type is dominant.
Dr Paulina Rajko-Nenow, a postdoctoral scientist in the NVRL said: “Our data strongly suggests that the strain that caused the outbreak in Cyprus is not directly linked to the one causing the ongoing spread of BTV-8 in Europe but is more likely to have been blown across the Mediterranean Sea from Lebanon or Israel to Larnaca”.
“Combining full genome analysis and atmospheric dispersion models has provided us with data that has been essential for us to pinpoint the outbreak origin. This method will be useful for tracing strains in other outbreaks and highlights that understanding how BTV can spread between countries, including in wind-borne midges, is important for disease detection and prevention”, Dr Rajko-Nenow added.
Image: Bluetongue virus (BTV) cores, credit Bioimaging, The Pirbright Institute
This research was funded by Defra, the Biotechnology and Biological Sciences Research Council (BBSRC), part of UK Research and Innovation, and supported by the European Virus Archive goes Global (EVAg) project that has received funding from the European Union’s Horizon 2020 research and innovation programme.