Summary
The geographic distribution of bluetongue (BT) viruses (BTVs) is governed by definable virus-vector-ecological/environmental relationships. The infection can only be transmitted by competent vectors. In the United States of America (USA), the New England States (Maine, Vermont, New Hampshire, Massachusetts, Rhode Island and Connecticut) and the northern tier of states from Maine to Montana are free of BTV because they are vector-free. Likewise, the eastern provinces of Canada are free of both the vector and the viruses. In Mexico, different virus-vector ecosystems exist in the northern and southern regions of the country. Historically, significant trade in cattle has occurred between Canada and the USA and the USA and Mexico. Although unrestricted year-round movement of cattle from BTV-endemic areas to vector-free and BTV-free areas occurs, BTVS have never been isolated from resident cattle in such virus-free areas in the USA. The authors discuss current BT-related requirements for trade within North America and elsewhere.

Keywords
Bluetongue virus, Canada, Culicoides, Cattle, Mexico, North America, Trade.