If the chickens are healthy and happy, I wouldn't treat them.
The idea of worm infestation is upsetting to all of us. None of us want to get worms, or want our food animals or pets to have them. But treatment without evidence may cause more problems than they solve.
This is a little off-topic, but some may find it interesting. There is a new wave in medical care called helminic therapy. It means worm therapy. Folks with MS, terrible allergies, asthma, and other immune disorders are purposely being infected with worms to relieve the symptoms of their disease. Many swear it works. The thought is that human beings have, until the last few generations in developed countries, been infected with parasites throughout their lives. Our immune systems evolved with a much greater exposure to parasites and more bacteria and viruses than we are exposed to now in our artificially clean homes and workplaces. So, the theory seems to be, our immune system doesn't have enough to fight, so it turns against us, and we develop an autoimmune disorder. The doctor gives you a slight case of worms, the immune system calms down (or has something else to concentrate on?), and the symptoms of an autoimmune disorder are lessened. It makes sense, in an "idle hands are the devil's workshop" kind of way.
I know, gross. But interesting.