This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Communicable Diseases, Subject name: Social & Preventive Medicine
Dengue hemorragic fever occurs in 
Select and explain. 
A. Malnourished patients, B. Immunocompromised patients, C. When type 2 infects a previously infected person, D. Persons having high grade fever
C: When type 2 infects a previously infected person
Answer: C: When type 2 infects a previously infected person 
Explanation: Ans) c (When type 2 infects a...) Ref park 20th ed p 218-221Dengue haemorragic fever (DHF) is a severe form of dengue fever caused by infection with more than one dengue virus.At least there are four serotypes of dengue virus (1,2,3 and 4)DHF is thought to be due to double infection with dengue viruses - the first infection probably sensitises the patient. While the second appears to produce an immunological catastrophe.Dengue fever is transmitted by Aedes mosquito . Transmission cycle is "man- mosquito-man" type.Bleeding manifestations are not seen in classical dengue fever. It is usually seen in Dengue hemorrhagic fever (DHF) and Dengue shock syndrome(DSS).There is haemoconcentration instead of hemodilution in DHF and DSS due to plasma leakage and thrombocytopenia which results in abnormal hemostasis.Usual rash seen in dengue fever is a maculopapular or scarlentiform rash seen on 3rd or 4th day of disease.lt is accompanied by itching and hyperaesthesia.lt last for 2 hrs to several days and may be followed by desquamation. (Refer Q137 Kerala 2009, Q125 kerala 2008for fur-ther explanation)