Abstract

luetongue (BT) is an infectious, arthropod borne viral disease of domestic and wild ruminants. BT is a notifiable disease of huge socio-economic concern and of major importance in the international trade of animals and animal products. Due to the segmented nature of genome, there is existence of high diversity in BT virus serotypes too as a consequence of genetic reassortments. Until 2004, BT was considered as an exotic disease in Morocco. However, from 2004 to 2015, at least two BTV serotypes (BTV-1 and BTV-4) were reported in the country. BTV-4 was introduced in September 2004 and produced an epizootic in northern Morocco but large vaccination campaigns with live attenuated vaccine contributed to the disease disappearance from the country. However, in 2006 and 2007, the widespread recrudescence and extension of a severe BTV infection in new areas with unfavorable environmental conditions suggest the introduction of a new serotype, BTV-1. Implementation of vaccination campaigns using a live bivalent BTV-1 and 4 vaccine allowed control of the disease, but, in 2009, BTV-4 re-emerged in the country after an epidemiological silence of 5 years, showing severe symptoms similar to BTV-1. Sequencing of the new BTV-4 virus showed a reassortant with at least 4 segments of BTV-1, likely to be a combination of the field virulent BTV-1 and BTV-4. The radial extension of BT infection across borders with the coexistence of many serotypes increases the risk for reassortment between different wild and attenuated serotypes, particularly those that occur in the Mediterranean Basin, where vector activity continues throughout the year. This review focuses on the current understanding, genetic diversity and transmission dynamics of BT, and the possible factors that may play a role in the spread of the virus in Morocco or neighboring countries.

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