10 month old has rash on head trunk spreading to bottom. Occasional low grade fever. Dr said WBC count was low and is viral. Wife has rash now.

Rash. So yes it does sound like a viral rash or exanthem of the skin and it easily spreadable or contagious to other individuals who are susceptible like other younger kids, immune suppressed individuals, or anyone else who hasn't been exposed to the virus in the past. As long as symptoms aren't worsening, there should be nothing to worry about in mom or child. See doc if worsening. Good luck.
Viral rash. It sounds like the doctor was right. He has seen the rash and I have not. I would listen to him/her. It should get better with time. There is nothing to do specifically.