Thanks to Krstofer for these images.
This shows typical spider mite damage on a Passiflora. The spider mites are difficult to see with the naked eye. Look for them underneath the leaves in a good light with a magnifying glass. They can greatly weaken or kill a small plant.
Spider mite infestations (in UK anyway) usually occurs indoors in dry conditions and are very hard to get rid of in greenhouses. They don't like humidity. Once the plants are outside they are usually shifted pretty easily by vigorous hosing with water or soap solution underneath the plant leaves from all angles for a few days running.