snip...
Blood-sucking insects, including mosquitoes, fleas, lice, ticks, and mites, are the main method of spread. Direct transmission is possible, usually by the aerosol route
..snip
I suppose that could mean it's spread by midges. My horse suffers from sweetitch which is spread by midges and it's a horrible thing to deal with. I've sort of got to hate midges more than wasps over the years!