Have Fever, Dry Cough, Muscular Pain, Anorexia, Abdominal Discomfort. Diagnosis?

hello,iam abubakr osman ,medical student ,from sudan can you help me to resove the following problem: A 22-year-old English woman living in Kenya complained of a constant frontal headache with fever which had been present for ten days. Treatment with chloroquine (600 mg base orally) had not produced any improvement. On enquiry she complained of anorexia , abdominal discomfort and constipation. She had a dry cough and muscular aches and pains. On physical examination she looked ill and had a rather sunken facies. Vital signs: temperature 40.5C; pulse rate 92/min; blood pressure 120/70 mmHg; respiratory rate 18/min. On auscultation, scattered rhonchi were heard throught both lung fields. On abdominal palpation there was generalized abdominal tenderness, but no rigidity or guarding. Bowel sounds were present. Her spleen was palpable at 2 cm below the left costal margin. Investigations: Haemoglobin 11.0 g dl-1; total leucocyte count 3.5 x 1091-1. Thick and thin blood films did not show malaria parasites. Chest radiograph , and urine microscopy and culture were all normal. Questions: Q1: What is the likely diagnosis? Q2: How would you confirm this diagnosis? Q3: What is the correct treatment? Q4: The patient initially made a favourable response to therapy. On the fourth day, however, her condition suddenly deteriorated; she was sweating and restless, pulse rate had increased to 120/min and blood pressure had fallen to 90/60 mmHg. What are the possible explanations and what would now be your management?