Parvo is a virus that can produce pain, rashes, and itching in humans. It generally effects the immune system, and commonly will go away on its own. However, some people
who already have immune system problems do develop severe infections with fevers and anemia, but this is rare. Treatment for Parvo is usually to help the symptoms only, as there is no cure.
Your son in law may have this virus, but it will probably go away in a month or so, and not cause him any other health problems. I do not think his high blood pressure had anything to do with him getting this virus. The virus is actually quite common, especially in children. It is spread from person to person (not from dogs), as we get infected with a different strain than animals. Fortunately for humans, it is not as serious as the strain dogs get.