Transboundary spread of pig diseases: the role of international trade and travel

Beltran-Alcrudo, Daniel; Falco, John R.; Raizman, Eran; Dietze, Klaas

With the ongoing process of globalization, the increasing movement, both formal and informal, of animals and their products poses a growing risk for animal populations to become exposed to TAD pathogens. A sound epidemiological understanding of how TADs may enter naive populations is essential to ensure preparedness of all stakeholders, to prevent the entry of pathogens through the different pathways, and to properly and promptly detect, investigate and control outbreaks. However, many countries, especially those in the developing world, lack adequate veterinary and diagnostic capacity to perform these actions. As a result, the source and pathways of primary or index outbreaks often remain unknown. This is perfectly exemplified by the latest ASF spread within the European Union and into China, where despite the high risk and alert levels, none of the last affected countries (Hungary, Romania, Bulgaria and Belgium) managed to identify or even narrow down the source of their index cases [128] . And yet, the source country or region can sometimes be narrowed down through phylogenetic analysis, which may point towards some more likely routes. For example, phylogenetic analysis of the UK isolate of the 2001 FMD epidemic, which started in a swill-feeding piggery, showed the greatest similarity to a South African virus [5, 94] . Strains of porcine epidemic diarrhea (PED) in the United States were almost identical with Chinese strains [56] . Similar examples for CSF have been compiled by Moennig et al. [68] . More recently, genetic analysis of the first ASF incursion in China proved its likely origin in Eastern Europe [128] .