I've had this not a nice illness.
I left it a good while before I exercised on the same advice, once the fever actual feverish period passed (about 2 weeks) I left it about 3 weeks before I started hitting the gym:
http://www.uk-muscle.co.uk/advanced-...need-back.html
My advice would be drink as much fluid as possible, I drank 5 litres of water every day and supplemented with Vitamin B12 amogst others, it was a sh1t period but I think these helped me through.
Don't be to keen to get back, rupturing your spleen is not like pulling a hamstring, once that bad boy tears you are in serious strife and in danger of bleeding to death so I would always air on the side of caution.