You don't need to disclose your MS unless it is obvious that there is "something wrong" with you:
you'd rather they know you have MS, then wonder if you've been drinking, if your gait is wobbly, for example.
You'd also need to disclose for some health insurance plans: some require a physical exam, and it would become known that you have MS. That doesn't necessarily mean you won't be covered: if the company has health insurance for all its employees, you'd have to be included, but it would mean disclosure.
You'd also have to disclose if you're wanting some "reasonable accommodation" from the employer so you could do your job, despite any disability that you now have. For example, if you need closer parking, or need an office space nearer a bathroom, or need to be cooler, or ...a whole host of other things that people have requested.
But if..at least for now..your MS is "invisible" and you simply want a job, then you don't need to disclose anything, and just apply as anyone would for the job you want.
...I am not a doctor, nor health professional, and don't pretend to be one, here.....