Can a high fever for several days with no other symptoms be an ms exacerbation?

Yes: Any autoimmune disease including MS can present like this. See your doctor.

Fever and MS: MS should not cause a fever. Often, MS will feel worse with a high temperature, either in the weather, or when you have a fever. In fact, a simple infection can make MS symptoms feel much worse. If you had a fever and fatigue, or if your old MS symptoms came back, the fever was probably the cause, but the MS probably did not cause the fever. You should not consider this to be a relapse of MS.

Not MS causation: Yes, MS patients do have susceptibility for infections, but relapses do not cause temperature elevation, and your high fever does need medical attention. Furthermore, elevated temps can promote MS pseudo relapses, and viral infections can trigger true relapses.