Hi Good Afternoon Doc,my Boyfriend Was Confine In The Hospital

Hi good afternoon doc,my boyfriend was confine in the hospital for more than 2weeks because of dengue,and hi is high blood too,his bp is 280/180,his heart and kidney is already checked and both are ok,but he is so weak and having seizure for 2 times,and very high fever. What is the cause of his high fever and high blood doc?thank you.