Q: Why is there a drop in fever at the peak of infection in dengue cases?

A:This may be true only in dengue haemorrhagic fever. Dengue fever (DF) is a severe, flu-like illness that affects infants, young children and adults, but seldom causes death. After the infected mosquito bites and transfers the virus to the patient, the virus multiplies in local lymph nodes and within 2-3 days disseminates via the blood to various tissues. The virus circulates for 4-5 days in the infected monocytes, and B & T lymphocytes. Most patients have virus in their blood when they present with fever and clear the virus from the blood within a day of breaking the fever. Symptoms usually begin 4 to 7 days after the infected mosquito bite. Sometimes it may be as long as 2 weeks before symptoms develop and these include sudden high fever, severe headache, backache, eye pain, muscle and joint pains (therefore also called bone-break fever) and a rash that may appear over most of the body 3 to 4 days after the fever begins. Generally, infants and younger children have a milder illness than older children and adults. In uncomplicated DF the symptoms usually settle down in 2 days, though classically it lasts about six to seven days, with a smaller peak of fever at the trailing end of the disease in a biphasic pattern - the initial phase lasting 3-6 days, remission lasting about one day, then 1-2 more days of fever. Some cases may develop Dengue hemorrhagic fever (DHF) and these have higher fever, unusual bleeding such as bleeding gums or nosebleeds and low platelet counts. A small proportion of DHF cases may develop dengue shock syndrome (DSS), which has a high mortality rate. In such cases the fever comes down suddenly (temperature may actually dip below normal - hypothermia) at the peak of infection. But these cases are relatively not very common.