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Introduction
Foot-and-mouth disease (FMD) is a highly contagious disease caused by FMD virus (FMDV) which produces an acute, local vesicular disease in cloven-hoofed animals including cattle, pigs, sheep and goats. Clinical signs of FMD include pyrexia, vesicular lesions on the tongue, feet, snout and teats and sudden death in young animals [1]. Features that contribute to the highly contagious nature of FMD include the large quantities of virus excreted by infected animals, the small infective dose, multiple modes of transmission, short replication times and high mutation rate resulting in constant antigenic changes. In countries where FMD is endemic there are direct losses due to mortality in young animals, treatment costs and decreased productivity in adults and growing animals. In countries which are free from FMD the cost of an outbreak can have serious economic and animal welfare implications from direct control measures and the loss of international trade [2,3].
FMD is endemic in many countries within Africa, and Asia. There are seven serotypes of FMDV (A, O, C, Asia-1, SAT 1, SAT 2 and SAT 3) [4], as well as numerous intratypic viral lineages (topotypes) that often exhibit a geographically restricted distribution. Serotype O is the most widespread serotype of FMDV [5]. During 2013, FMDV positive samples collected in Libya were characterised as containing viruses from the O/ME-SA/Ind-2001 lineage, closely related to FMD viruses circulating in the Indian subcontinent [6]. This lineage subsequently spread westwards to cause FMD outbreaks in Tunisia (2014), Algeria (2014-2015) and Morocco (2015). Prior to these events in Tunisia, Algeria and Morocco, no cases of FMD had been reported since 1999, when the O/WA/Maghreb-99 strain originating from West Africa caused a series of FMD outbreaks in these countries. In addition to these cases in North Africa, separate introductions of the virus from the Indian sub-continent were responsible for FMD cases in the Gulf States including Saudi Arabia (2013), UAE (2014) and Bahrain (2015), as well as spread east into Laos, Vietnam and south into Sri Lanka. Further exotic outbreaks during the summer of 2016 in the state of Mauritius in the Indian Ocean have also been due to this lineage. There is now concern that this new lineage could establish itself in these regions and out-compete...