The dengue virus induces a peculiar increase in permeability characteristics of the blood vessels leading to uncontrolled fluid movement from the bloodstream to the surrounding tissues. It is also known as the “leaking” of fluid from the bloodstream into the adjacent areas and is commonly referred to as the “leaking phase.” This situation leads to reduced fluid within the circulating compartment and is associated with a fall in blood pressure and cardiovascular malfunctioning. The patient presents in a state of collapse or shock. This is known as the “Dengue Shock Syndrome.”

In addition, the virus causes a certain amount of direct damage to the blood vessels, which leads to a bleeding tendency. The disease also causes a fall in the platelets of the blood, enhancing the bleeding as platelets are intimately involved in the clotting processes of normal blood. This is known as “Dengue Haemorrhagic Fever.” The bleeding manifests as spots on the skin or internal haemorrhage, particularly in the stomach and intestines, and this presents as brownish or blackish “coffee grounds” material in the vomitus or black faeces. 

In some rare cases, the heart is affected, leading to a complication known as myocarditis which leads to heart failure. This particular complication can be troublesome and needs to be managed very carefully. All these complications are associated with an increased rate of fatalities. However, with competent management, these fatalities could be reduced drastically.  

It is essential to point out that the child remains conscious and alert throughout the illness, even when they are quite ill with the dreaded complications. These complications cause death and are much more common during second and subsequent attacks of the disease. The standard, uncomplicated form starts with a high fever and vomiting, and the patient generally feels unwell. The period around the 4th to the 7th day is crucial for the development of the complications. However, many affected individuals go through the illness just like any other form of flu and recover without any problems. However, the more severely affected children feel quite ill, especially during the late phase of the disease that comes on after 3 to 4 days.