Since the 1980s it has been carried into most other beekeeping regions of the world, killing thousands of colonies. See the animation . There is international trade in live bees. Queen bees are shipped world-wide, and are believed to be responsible for the spread of the mite from Europe to both North and South America. New Zealand has not permitted imports for many years, but does export live bees.
Beekeepers shift their hives long distances to pollinate crops, or gather honey.
This enabled varroa to spread throughout the USA within a few years of being introduced. The whole bee population is at risk of getting the mite. Numbers of mites in a colony typically build up over several years, and untreated colonies die. Sudden hive crashes.