Regarding infectious mononucleosis, his EBNA IgG is positive, which suggests past infection. Since EBNA IgM is negative, it rules out acute infection.
For rickettsia, weil felix is not a very test to diagnose. Besides, this child has no rash, eschar and no response to chloramphenicol. Doxycyline was avoided as there was no clear evidence of rickettsial infection and the child is only 5 years of age.
The other differential diagnosis that most of you have suggested is autoimmune, JIA. That is exactly what we thought and started the child on
Naproxen to which his fever has responded in 5 days. He required
Naproxen for a month and then has had no fever. He is on regular follow up and is asymptomatic at the moment.