This is an aphid infestation, specifically Currant Blister Aphid, see here https://www.rhs.org.uk/biodiversity/currant-blister-aphid for information, though its a UK link so some of the treatment products mentioned may not be available where you are.
I would absolutely not recommend malathion as a treatment; if you want to choose a pesticide, choose one intended for edible plants/crops, as mentioned in the link. Now that the leaves have bubbled and developed red patchy areas, any treatment you carry out will not get rid of those, and actually, the plant usually carries on growing and fruiting regardless of the presence of these aphids. Non pesticide treatment methods include spraying the insects off with water using the hose pipe, wiping them off with your fingers, or using horticultural oil sprays such as neem, although they are fairly short acting, so repeat treatments will likely be necessary. It is not really necessary to remove and burn affected leaves.