Dengue fever is a relatively common problem that periodically reaches epidemic proportions, usually every 4-5 years. Dengue occurs due to infection by a FLAVIVIRUS, which is transmitted by the bite of the Aedes aegypti mosquito. It is very rarely fatal in healthy and fit individuals. The patient is often left debilitated and requires considerable convalescence. Dengue is not transmitted from person to person.
Following an incubation period of 2 - 14 days (usually 4 - 8), the onset of symptoms is usually abrupt with chills, headache, backache, weakness and pain behind the eyes. The joint and back pains can be very bad indeed; hence the older name 'backbone fever'. The temperature rapidly rises, often to 40°C (104°F), and there is a low heart rate (compared to the other causes of high fever). The blood pressure is often also low.
Recurrent infections with Dengue fever, especially when they are from different strains of the Flavivirus, are associated with a higher risk of complications, in particular Dengue Haemorrhagic shock syndrome (covered later in this bulletin).
After 2 - 4 days, a temporary improvement can occur with a sudden drop in temperature and subjective improvement, usually for 24 hours until there is a second rapid temperature rise, and the appearance of a characteristic rash on the trunk, limbs, palms and soles especially. The skin in these areas turns bright red (the rash is usually a series of dots) and may peel. (This second phase of fever does not always occur). Thereafter there is slow improvement. An attack produces immunity for a year or more, but only to the one of the four FLAVIVIRUS strains responsible.
CONFIRMING THE DIAGNOSIS
There are no immediate useful tests for diagnosing dengue fever. The white blood cell count is often low unlike in bacterial causes of fever. The dengue antibody test can give both false positive and false negative results, especially in the first week of the disease. The diagnosis will, in a large proportion of cases, be based on clinical presentation and a characteristic drop of platelets in the blood.
Convalescence can take weeks, and bed rest and fever lowering medications are required. Do not use Asprin.
DENGUE HAEMORRHAGIC FEVER (DHF)
A rare complication of dengue fever, dengue haemorrhagic fever, can occur, most often in small children and elderly adults. This can sometimes be a serious illness. If DHF occurs it will usually do so by day 3-5 of the fever.
It has been suggested that DHF is more likely if the patient has previously had an attack of dengue within the last calendar year, and that the occurrence of DHF relates to this previous exposure. The relationship between DHF and previous dengue infection is not this clear-cut, however previous exposure does raise the incidence of subsequent DHF, in particular when this involves different strains of the virus.
SYMPTOMS OF DHF
Uncontrolled bleeding distinguishes this from uncomplicated dengue fever. Bleeding can occur from the gums, nose, intestine, or under the skin as bruises or spots of blood especially under a tourniquet - this test should be employed if there is any suspicion. The liver is often enlarged.
Patients can have rapid onset of marked drowsiness, lethargy or restlessness or the presence of shock as manifested by a rapid and weak pulse, low blood pressure and cold clammy skin. Such patients should be immediately referred to a good hospital for further management. DHF shock can be a mortal illness and requires rapid and careful in-hospital management with replacement of fluid, electrolytes, plasma and sometimes fresh blood / platelet transfusions.The most useful laboratory test in suspected DHF is the estimation of thrombocytes (platelets) which will be very low. In contrast to uncomplicated dengue fever the white cell count is more often high in patients with DHF.