It's a little hard to tell, so close up and with light coming through it, but I am thinking it is not disease, but some kind of sucking or chewing insect pest. Inspect your plant thoroughly including undersides of leaves, stem-leaf joints. A magnifying glass would help, since some of the pests that could do this are very tiny. Try shaking your plant over a piece of white paper. One thing that could cause this damage is thrips and they are tiny (1/25th of an inch or so). They would show up on the paper as tiny threads.
If you don't find anything come with a flashlight and do the inspection and test again after dark.