Dengue fever is a viral disease transmitted by mosquito Aedes Aegyhti or other species of this genus. It is endemic in many countries of ASIA, AFRICA central and South America, All ages and both sexes are liable to get infection.
The virus is filterable and four sero types called DEN-I, DEN-2, DEN-3 and DEN-4 exist. All four serotypes cause disease but serious form of disease (DHF and DSS) are associated with sero types DEN-2 and DEN-3. The mosquito feeds primarily on humans during the day time and becomes infected when they take a blood meal from viremic person.
Humans are infective during the first 3 days of high body temperature. Viremia in humans is present for about 24 hours prior to onset and on average five days after onset of illness. Mosquitoes that become infected require incubation period of about 8-14 days before they can transmit Dengue fever virus to another person.
Mosquito once infected remains so for life. Its viruses are not communicable and person to person transmission does not occur and an- infected person is not infectious to other persons though it remains infectious for mosquitoes for an average of about 6 days
Clinical features
The incubation period is generally 5-10 days but sudden onset may occur in about 50% of cases. Classic dengue fever has three phases.
I. The stage of invasion
2. The stage of remission
3. Stage of secondary rash / terminal temperature
A case of dengue fever presents with general malaise, high body temperature and pains in the limbs. Temperature raises suddenly going upto 150°F. There is chilly sensation, severe headache, backache, reto orbital pain. Face becomes congested and flushed. Restlessness and insomnia appear. Pulse may vary from rapid to slow.
After 3 to 4 days temperature falls by crisis and now symptoms improve. But after a period varying from 12 hours to 3 days, the temperature rises again. This is often referred to as ‘SADDLE BACK FEVER’ which is characteristic of dengue fever. A roseolar rash simulating measles may appear on the face, neck and arms.
It is transient to start with but definite rash may appear on trunk on third to 5th day. It is pmritic and may persist for two weeks. Lymphadenopathy and petechiae on the soft palate may be seen. After two to three days of appearance of rash, temperature subsides but leaves a feeling of marked weakness and depression for several weeks. Blood count is low with lymphocytosis but by 3rd to 5th day there is leucoplenia and neutropenia.
Deugue has to be differentiated from influenza, rheumatic fever and other exanthemata. For a classic case of dengue fever many investigations are not required.
Treatment is symptomatic. Bed rest, paracetomal and plenty of fluids are helpful. Patient should preferably be kept in bed for at least 3 days after the temperature has subsided. As recovery takes place, good nourishing diet is advised to tide over the generalized weakness.
An uncomplicated case of dengue fever carries good prognosis. It is a self-limiting disease though recovery often leaves behind marked tiredness and weakness.
Dengue hemorrhagic fever
It is a severe form of dengue fever and all four serotypes can cause it but it occurs when several types of virus are present at the same time. Infection with DEN 1, 3 or 4 followed within few years by DEN-2 may be important in its pathogenesis.
DHF is immunologically mediated disease and at one point was considered to be a disease of childhood but now it is equally prevalent in all age groups. Prior immunity to different types of dengue fever virus is important in the production of severe form of disease.
Clinically there is abrupt onset of high body temperature with headache, body pains, cough, anorexia, nausea and vomiting. These signs are just like in any case of dengue fever but within 24 hours after the temperature falls to normal or below normal, there is sudden deterioration in health.
Patient goes into a state of shock with cold clammy extremities and peripheral circulatory failure. Hemorrhages appear into the skin and various other sites. Patient may have epistaxis, bleeding gums, hematuria, haematemesis and malena and may go into a state of shock (DSS).
There is fall of blood pressure with a week thready pulse. Liver is enlarged (LOBULAR HEPATITIS). Often patient goes into a state of coma which is a poor prognostic sign. Most fatalities occur on fourth or fifth day of illness.
Diagnosis
It is based on virus isolation which can be made by mosquito inoculation and by using C6136 mosquito cell culture. Virus is identified and detected by immuno-fluorescence using serotype specific monoclonal antibodies.
Demonstration of rising antibody titres by Ham-agglutination inhibition or complement fixing test are helpful. Dengue fever blot assay test is considered specific. ELISA test for 1gM and IgG antibodies is also a useful test. The most characteristic findings are Thrombocytopenia (Platelet count less than 75,000 per mieroliter) Prolonged bleeding times, depression of clotting factors V, VII, IX and X. Tourniquet test is positive.
Prothrombin time and partial thromboplastin time may be normal or deranged. Their values are important in predicting bleeding. Thus tendency to bleed is greater when PEr is prolonged more than 30 see. In addition to above patient of DHF / DSS may have hyponatremia, Aeidosis elevation of blood urea and transaminase levels.
Dengue shock syndrome (DSS) is characterized by a weak thready pulse, cold extremities and restlessness. It falls into grade Ill/Grade IV of WHO classification.
Treatment
Early replacement of lost plasma with electrolyte solutions is the main stay of treatment. 5% glucose solution in 0.5 N.Saline administered at a rate 40 ml /kg shall restore blood pressure. Rapid replacement of fluid shall prevent disseminated intravascular coagulation.
Early recognition of shock is very important. Hypotension, a sudden rise in hematocrit or continuously elevated hematocrit values despite administration of fluids are ominous signs. Measuring of urinary output is another important parameter.
Oxygen should be administered to correct abnormally low blood oxygen. Blood transfusion is contraindicated unless there is severe plasma leakage. Where there is suspicion of internal bleed, fresh whole blood should be given. Antibiotics are not required. Salicylates should be avoided and so sympathomimetic amines.
Since there is doubt about severe disseminated intra-vascular coagulation, role of Heparin is controversial though it is used in some cases. Role of steroids is also doubtful though in cases of shock they may help.
Recovery from circulatory collapse occurs within 24 to 48 hours. Platelet count can be a predictor of mortality with deaths six times greater in those with platelet count less than 50,000/cmm. Survival after infection with one virus sero type confers life long immunity to reinfection with that sero type but not to the other three sero types.
Prevention
Vector control is important.Since Aedes aegypti feeds primarily on humans during the day time and is found mostly in human habitations, attempts be made to destroy the mosquito which generally is present in pots, discarded cans, flower vases and water coolers. Spray insecticides. Use of mosquito repellents and sleep under mosquito nets be advised. Avoid wearing clothes that expose arms and legs.
Prognosis
A simple case of dengue fever carriers good prognosis but cases with severe form of DHF/ DSS carry poor prognosis. Case fatality is from 2 to 5 per cent.
