Sounds like spider mites... at least here in the U.S. that would be my first suspicion. They're nearly invisible but their eggs are easier to see... look like tiny Christmas Tree ornaments on the underside of the affected leaves.
Treat mites with any good sulphur based miticide.
There are other possible causes, but since yours are greenhouse grown some of the the othe 'usual suspects' are eliminated... BTW... left untreated your plant is sure to die... and yes... the mites will spread to other plants...
(As an off question... you haven't used any herbicides any where near the plant have you?)