To trap feral cats/kittens, you get a live animal trap, put newspaper along the floor so it's comfortable for them to walk in, and bait it with some tuna/soft food-the stinkier the better. Cover the trap with a light sheet, except for the enterance, of course. Then walk off (get in your car with the window cracked, maybe drive around the corner of the building, but stay within earshot. As soon as you hear the trap's door spring, you have to get out there and cover the front, too, so the cat can't see anything (freaks them out a lot less).
Chances are, it's not neutered, so you can get that done, too. They can take a look at him from there. Feral cats are *very* difficult to control with your hands (grabbing the fur on the back of their necks), but kittens aren't as hard (easier to hold up a tiny kitten by it's neck fur than an adult. The vet can examine him and get him the necessary treatment. I once had to pill a semi-feral cat twice a day for a couple of months. She was quarantined (for a bite), got a URI at the shelter where she was quarantined, and nearly died. What a mess. Pilling her took two people, thick gloves, and a thing that shoots the pills down her throat. She stayed in a large dog crate during this time.
If you choose to go this route, good luck. I'm guessing there isn't animal control in the area if it's rural, so that's probably not an option (he'd be put down in all likelihood, too).