other Orbiviral diseases
Like BTV, epizootic haemorrhagic disease virus (EHDV) is multi-typic, affects ruminants and is transmitted by Culi- coides. EHDV has an almost worldwide distribution but has not yet been recorded in Europe.
Nevertheless, it has recently expanded northwards — in 2006 EHDV9 was identified in Morocco, Tunisia and Algeria, and EHDV7 in Israel(38), and in 2007 EHDV6 was identified in western Turkey, all for the first time(39). These range extensions and the disease caused in cattle persuaded OIE to re- classify EHD as notifiable from mid-2008(40). European cervids (red, fallow, roe and muntjac deer) were experimentally infected with EHDV1 but did not develop clinical signs. However, cell culture passaged virus was used in all but three deer, a procedure that tends to attenuate orbiviruses. Otherwise there seem to be no published data on EHDV in European wild mammals. In view of this paucity of information and, as EHD is one of the most important diseases of deer in North America, its emergence on the threshold of Europe is a matter of concern.African horse sickness (AHS) has a similar epidemiology to BT and EHD but affects equids. The horse is an indicator species, and in naive populations mortality rates exceed 80%. Lower but significant mortality also occurs in mules and donkeys. Zebra support virus replication but rarely exhibit clinical disease. AHS virus (AHSV) has a track record of extension from Africa across the Middle East to India, and also into Iberia. Recently increased AHSV activity has been detected in Ethiopia and West Africa, from where it has previously invaded Europe(41).
In addition to EHDV and AHSV, other exotic orbivi- ruses are known or suspected of causing disease in ruminants (e.g. the Palyam viruses) or equids (e.g. equine encephalosis virus (EEV)), but there is no published information on their effects in European wild mammals.
In common with BTV, EHDV and AHSV, EEV may be extending its range and has recently been identified in Israel. All of these recent O rbivirus range changes may be linked to high vector mobility and ongoing climate change.REFERENCES
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