To clarify...
Cardinals, both male and female, may experience parasites, or head molts.
The most noticeable, in this part of NC, in July, is the male cardinals going bald, specifically most noticed in July. It may be the males are more noticeable, due to their normal plummage suddenly disappearing, makes them stand out more, with their little bald black heads, with that bright red body, giving the impression of a tiny red vulture. It is not confined to my immediate backyard, either.
Due to the fact it is all over the region, and not just localized to my feeder area, is why I suspect it's a seasonal head molt, and not a parasite, in the birds males I have seen. If my feeder contained parasites, I would see this during other times of the year, possibly with the females and babies, or other among other birds, and no one else, over a hundred miles from me, would be seeing the same thing, at the same time of year.
Your female cardinal, Indianabirdlover, is a female, and taken earlier in the year, and you didn't notice other cardinals with the same lack of feathers, the female in the photo may very well be due to parasites.
I believe both to be the culprits, with birds, yes. But when I see a bald male cardinal in July in NC, I expect to see other bald male cardinals, in July in NC and I do. I do not attribute it to parasites, unless I see research done, that a parasite is most prolific in July and the cause of male cardinals losing their head feathers in July in NC. Which I have not seen. By the end of August, everyone has their head feathers back, and I do not see this occurence again, until around July the following year.
If you see only one or two, it may very well be parasites. If you see nothing but bald male cardinals all over the place, say in March... and the following year, you see the same thing again, at the same time, it could be a seasonal molt you may not have noticed before and not parasites.
Even the experts say they do not have enough information to say for certain, but the proof is out there from reports of birdwatchers, that support the theory of seasonal head molt and dispute that it is only caused by parasites.
For me, the proof is in the fact I only see this in July, on a large scale. If I see a bald male cardinal in October, I would suspect parasites, and clean my feeder. 
