Dengue hemorrhagic fever is caused by:

Ans. is 'c' i.e., Reinfection with a different serotype of dengue virusDengue hemorrhagic fever is a most severe manifestation of the disease. The initial classic phase of dengue hemorrhagic fever is similar to that of dengue fever and other febrile viral illnesses. But, subsequently, the condition of the patient suddenly worsens with shock and hemorrhage, especially into the gastrointestinal tract and skin. The hemorrhagic manifestations include bleeding from nose, melena and hematemesis. This condition shows a high fatality rate as high as 10%. It occurs in children with passively acquired maternal antibodies. It may also occur in a person previously infected with a different serotype of the virus, showing non-neutralizing heterologous antibodies in the serum.