It's a plot.
Nanites released by organizations during periodic high intensity atmospheric activity; which is actually driven by other interests using Tesla based communications and high energy transfers, but some folks throw up some stuff into the air out in the Gobi Desert, and use these disturbances as a transfer mechanism. Plot occurances of that fiber disease and you'll trace the wind pattern of a particularly dense plume a few years ago. Other plumes contain vacinating nanites. It's a frelling soup o' stuff up there. The C-trails are more of a remediation program, really.
But I say too much.
'Cept for: Follow the Yttrium.