A 2-year old girl presents the recurrent episodes of diarrhea (mucus and blood at times), hepatosplenomegaly, perianal excoriation and resistant oral thrush. She weighs 6 kg and measures 78 cm in height. The most likely diagnosis is:

The child is most probably suffering from HIV infection. The clinical picture described in this question like recurrent diarrhoea, resistant oral thrush, gross underweight with hepatosplenomegaly are seen in HIV infection (AIDS). This clinical picture is absent in rest of the three conditions.