Ans. is 'c' i.e., Dengue fever o Break bone fever (Saddle back fever) is caused by dengue virus.Dengue fevero Dengue fever is caused by arboviruses (at least 4 serotypes have been recognized)o It is transmitted by Aedes (Aedes aegypti is the main vector).o The reservoir of infection is both man and mosquito,o The transmission cycle is Man-mosquito-mano Dengue fever occurs both epidemically and endemically. Epidemics starts in rainy season and are usually explosive.o Aedes mosquito becomes infective by feeding on a patient from the day before onset to the 5th day of illness.o Various manifestations of Dengue infectionClassical dengue fever - Also known as break bone feverIncubation period 2-7 days (3-10 days - Park)Onset is sudden with chills and fever. Fever is usually between 39degc and 40degc temperature returns to normal after 5-6 days or subside on about the 3rd day and rise again after 5-8 days after onset (saddle back fever).Rashes appear in 80% of cases during remission or during second febrile phase. The rash lasts for 2 hours to several days and may be followed by desquamation. Dengue Hemorrhagic fever (DHF) -It is a severe form of dengue fever caused by infection with more than one dengue virus.The severe illness is thought to be due to double infection with more than one dengue virus.Dengue hemorrhagic fever is believed to result from reinfection with a virus of different serotype ( due to enhancing antibodies)DHF usally occurs after sequential infection with any two of the four serotypes of dengue virus.Sequence of infection may be important; serotype 1 followed by serotype2 is more dangerous than serotype 4 followed by serotype 2.Criteria for clinical diagnosis of DHFClinical diagnosisFever -Acute onset, high continuous lasting 2-7 days.Hemorrhagic manifestationsPositive tourniquet testPetechiae. purpura, ecchymosisEpistaxis, gum bleedingHematemesis and/or melaenaEnlargement of liverLaboratory diagnosisThrombocytopenia (100, OOO/mnV or less)Haemoconcentration haematocrit -->> increased by 20 percent or more of base-line value.C) Dengue shock syndromeThe clinical diagnosis is based on:All the above criteria plusShock manifested by rapid and weak pulse with narrowing of the pulse pressure to 20mm Hg or less or hypotension with the presence of cold clammy skin and restlessness.