Dengue Hemorrhagic Fever

01/01/2009

Very appropriately for a tropical country such as Thailand, there was a session on tropical hematology during the recent ISH Congress. Dr. Suchitra Nimmennitya a former director of the Queen Sinkit National Institute of Child Health in Bangkok made a comprehensive presentation. She differentiated between dengue fever, a non-fatal disease, and dengue hemorrhagic fever, a lifethreatening disease. In the latter there is an abnormal hemostasis and plasma leakage as a result of vascular permeability resulting in ascites, pleural effusion and hypovolemic shock complicated with a bleeding diathesis.

The pathogenesis involves humoral as well as cell-mediated immune responses to a second dengue infection of the four distinct dengue subtypes. There is immune complex formation, cytokines activation leading to vascular permeability, disseminated intravascular coagulation (DIC) and abnormal hemostasis. A rise in hematocrit on or about the 4th or 5th day and a drop in platelet counts signals a dangerous period of the disease. There is bone marrow suppression, atypical lymphocytosis, followed by
leucopenia and subsequently anemia.

Metabolic acidosis and hypoproteinemia are present. There is a shortening of the platelet half-life to 16 hours followed by increase in FDP and D-dimers. A prolongation of the PTT is often seen, at times not correlated with the bleeding. Liver enzymes are elevated transiently.

Therapy includes hydration preferably with Ringers lactate. Fresh frozen plasma and cryoprecipitate can be used. They do not use corticosteroids, but if bleeding is severe are using rFV11 (Novo seven), 40-100 mcg/kg. Two doses at 20 to 120 minute intervals are used.

A hemaphagocytosis syndrome has been observed in some patients.

Dr. Norman Maldonado
Secretary General IAD