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     Tropical Diseases

Malaria   |   Dengue Infection   |   Japanese Encephalitis   |   Diarrhea   |   Filariasis   |   Viral Hepatitis

The causative agent of denfue hemorrhagic fever (DHF) is dengue virus, of which there are 4 serotypes.

When a person is infected with dengue virus for the first time, clinical signs and symptoms are usually mild. However, if he/she is reinfected with a different type of dengue virus, severe conditions such as bleeding or shock will occur and can be fatal. This disease is usually found in children less than 15 years of age.

   
Transmission
 

Aedes aegypti is the main mosquito vector that transmits the dengue virus from person to person. When a female Ae. aegypti feeds on a dengue virus infected person, the viruses multiply in the insect body and remain there for the whole life span of the mosquito, approximately 1-2 months. Viruses are then transferred to another person being bitten by an infected mosquito.

Ae. aegypti can be found both inside and outside houses. They prefer to feed during the day. Their breeding places are containers with clear water, for example, jars, vases, ant traps, dishes, cans, pots, flower pots, tires, etc. The prevalence of DHF increases in the rainy season when the mosquito vectors are abundant and children often stay indoors during the day. However, in big cities such as Bangkok, this disease occurs sporadically all year round.

   
 
    
   
Symptoms
 
Approximately 80-90% of persons infected with dengue virus for the first time are asymptomatic. Hign fever, headache, muscle and joint pain, and minute bleeding spots under skin may be found in some cases. A second infection with a different type of dengue virus, however, causes more severe conditions, which can be divided into 3 phases :
  1.
Initial febrile phase - patients suffer continuous high fever, which may cause febrile convulsion in some children. Other symptoms are anorexia, nausea, vomiting and abdominal pain. Facial flush and hemorrhagic spots over the body, arms and legs are common. This phase usually lasts 2-7 days.
  2.
State of shock - the fever has subsided at this stage; patients feel drowsy with profuse sweating, cold hands and feet, weak but rapid pulse rate, pain at the right coastal margin, reduced urine output, and easy bleeding such as nose-bleed, vomiting of blood and bloody stool. In severe cases, blood pressure drops drastically resulting in shock and can lead to death. This phase lasts 24-48 hours;
  3.
Recovery phase - patients' conditions are improved as shown by good appetite, normal blood pressure, strong and slow pulse, and normal urine output. Bleeding spots under skin are still present over the body in some cases.
   
 
      
   
Diagnosis
 
Standard criteria of the World Health Organization for the diagnosis of DHF are high fever, easy bleeding (positive tourniquet test, bruises, nose-bleed, gum bleeding, etc.), abdominal pain at the right costal margin because of the enlargement of the liver, shock, decreased platelets, and hemoconcentration. Serological and/or virological investigations may be performed to confirm the diagnosis.
   
Treatment
 
There is no specific antiviral treatment. Symptomatic and supportive measures are most important. To lower the temperature during the febrile phase, acetaminophen should be given. Aspirin must not be used since it is known to cause bleeding. An antiemetic can also be given to prevent nausea and vomiting. Juice or oral rehydration solution in small amounts given frequently are helpful. Close observation for early signs of shock is necessary. The critical period is at the transition from the febrile to the afebrile phase. Parents should be advised about the warning signs of shock, such as, reduced urination, restlessness or drowsiness, coldness of extremities, or fainting. If these symptoms occur, the patient should be hospitalized immediately.
   
Prevention
 
The goal for the prevention and control of DHF is the control of mosquito vectors by several means, such as :
  1.
Preventing children/adults from being bitten by a mosquito vector; using a bed-net, even during the day, is advisable.
  2. Eliminating breeding places of mosquito vectors inside and around houses by
                  - changing water in containers, such as flower vases, every week
                - getting rid of unused, broken objects, such as old tires, flower pots
                - putting guppies or other fish that feed on mosquito larvae into lotus ponds or other water sources
                - all water containers should be covered; the use of larvicidal sand granules (temephos) in water storage
                  tanks to destroy the mosquito larvae is advisable
                - mixing salt or vinegar with water in ant traps
   
 

  


Last updated: March 20, 2013
 
 
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