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Dengue Fever
Updated 9/2001
Primary Distribution:
East and West Africa, Southeast and East Asia, Pacific Islands,
Eastern Australia, Central and South America, Mexico, South Texas, Caribbean
Islands - with distribution increasing, especially in urban areas. Dengue
fever is intermittently reported from Southeastern Texas. With approximately
150,000 deaths annually, dengue is now the tenth leading cause of death worldwide.
There are approximately 80-100 million new cases annually worldwide and approximately
40% of the world's population live in an area at risk for dengue (Chin, 2000;
World Health Organization [WHO], 1998; Ericsson, 1998).
Agent and Vector:
Dengue viruses (DVs) types 1, 2, 3, 4 (Togaviridae, Flavavirus) are
transmitted by Aedes aegypti mosquitoes. There is increasing incidence and
prevalence of cocirculation of multiple serotypes.
Incubation: 2-10 days.
Clinical Findings
and Treatment
Signs and Symptoms: After the infected mosquito inoculates the host, the virus is replicated in local lymph nodes and within 2-3 days disseminates via the blood to various tissues. The virus circulates for 4-5 days in the infected monocytes, B cells, and T cells. Most patients are viremic at the point of clinical presentation with fever and clear the virus from the blood within a day of breaking the fever.
Dengue is usually a self-limited
illness characterized by abrupt onset high fever, chills, headache (frontal/retro-orbital)
especially when pressure is applied to the eyeballs, rash, signs of bleeding
(epistaxis, gums, petechiae, menometrorrhagia), changes in taste, sore throat,
nausea, vomiting, diarrhea, anorexia, depression, and severe aching myalgia
and arthralgia (hence the term, "bone-break" fever). In uncomplicated
dengue the syndrome usually abates in 48 hours.
Fever is usually biphasic
with the initial phase lasting 3-6 days (sometimes with swelling of hands
and feet), remission lasting about one day, then 1-2 more days of fever. The
rash is also biphasic usually beginning during fever remission and lasting
several hours to several days. The rash is usually characterized by scarlatinaform
macules beginning on the dorsum of the hands and feet, spreading centrally,
and sparing the face; and may also be morbilliform, macropapular, or petechial;
and followed by desquamation. Pervascular edema with diapedesis of RBC and
widespread focal hemorrhages may also occur when the inflammatory response
produces a vasculopathy which can lead to shock (Gubler, 1998; Rigua- Perez,
1998; Tsai, 2000; Vaughn & Green 2000). Convalescence can vary from days
to weeks.
Complications:
Unfortunately there is no durable cross protection between the four dengue
viruses. However, after two bouts of dengue there is rarely a third bout and
even rarer a fourth bout. There may also be an immune pathological response
in some patients (often the result of an heterologous immunity), which results
in the syndromes of dengue hemorrhagic fever (DHF) and dengue shock syndrome
(DSS). Meningoencephalitis occurs in 5-10% of children with dengue. Shock
in DHF and DSS follows the sudden extravasation of plasma into extravascular
sites including the pleural and abdominal cavities. DHF occurs when immune
status is suppressed or when a second infection is from serotype 2, though
any of the common serotypes may cause hemorrhagic fever, especially among
children. DHF is characterized by petechial rash, gastrointestinal bleeding,
and fluid leaking into serosal cavities and tissue spaces. While DHF is probably
a result of secondary infection and/or viral virulence, DSS results from vascular
permeability and shock from massive plasma leakage and is characterized by
rising hemocrit, hypoproteinemia, serous effusion, hypotension, narrow pulse
pressure - which can lead to circulatory collapse and sometimes death. DSS
sometimes occurs in infants born to mothers who are immune to dengue fever.
Other, less common complications are depression, pneumonia, bone marrow failure,
iritis, orchitis, and oophoritis (Chin 2000; Chuansumrit, Phimolthares, Tardtong,
Tapaneya-Olam, Kowsathit, & Chantarojsiri, 2000; Tsai, 2000).
Laboratory Findings: Pancythemia may occur after 3-4 days of illness, characterized by leukopenia < 2000, mild acidosis, and hypoproteinemia. Platelets rarely fall below 100,000. PT and PTT are within normal limits. ECG changes may include bradycardia, ecotopy from the ventricules, flattened T waves, and prolongation of the P-R interval (Halstead, 2000). Additional or common hematologic changes in DHF and DSS include: hemoconcentrations of >20% in hematocrit, thrombocytopenia, prolonged bleeding time; and decreased PT that is seldom <40% of the control. Chest x-ray may reveal pleural effusions (left > right). Elevated hepatic transaminase levels have been reported in over 80% of dengue cases with no relationship to concurrent hepatitis B or C infections (Carlini, & Shandera, 2001; Tsai 2000; WHO, 1998; Halstead, 2000).
The tourniquet test is
frequently positive. A tourniquet test is used to assess if capillaries can
withstand increased pressure which is important to assess as the vasculopathy
that leads to DSS and DHF which is often first visualized in the form of petechiae.
The tourniquet test is assessed by inflating a blood pressure cuff on an arm
to above venous pressure (70 mm Hg) for 5 minutes and then relieve the pressure.
Inspect the extremity for petechiae. If there are > 2 petechiae then the
test is positive. This test does not have high specificity. Interfering factors
with this test are women that are premenstrual, postmenstrual and not taking
hormones, or those with sun damaged skin, since all will have increased capillary
fragility. Large petechiae are associated with thrombocytopenia. (Pagana,
& Pagana, 1998; Tsai, 2000).
Diagnosis: Except
for the presence of the rash, dengue fever is difficult to distinguish from
other febrile illnesses (e.g., malaria, yellow fever, influenza) or arboviral
disease with dengue-like courses (e.g., Colorado tick fever, Rift Valley fever,
Ross River fever, sandfly fever). For this reason, an initial diagnosis may
be "dengue-like disease." Serologic diagnosis is on the basis of
a fourfold or greater increase in antibody titer in paired sera by hemagglutination
inhibition, complement fixation, enzyme immunoassay, or neutralization test.
Typically, paired samples from patients utilize IgM capture ELISA and indirect
IgG ELISA. Detection of DV specific IgA serum antibodies by indirect immunofluorescence
assay is diagnostic of dengue fever. Viral RNA can be detected by specific
complementary DNA probes or amplified first by a polymerase chain reaction
(Carlini & Shandera, 2001; Gren, Velzing, Copra, Balentien, Deubel, Vorndam,
& Osterhaus, 1999; Vaughn & Green 2000).
Differential Diagnosis:
The major differentials include early stages of malaria; mild yellow fever;
influenza and viral respiratory diseases; viral hepatitis; typhoid; and leptospirosis.
Four arboviral diseases have a dengue like course without a rash: Colorado
tick fever, Rift Valley fever, Ross River fever, and sandfly fever (Halstead,
2000).
Treatment: Treatment
of uncomplicated dengue is primarily supportive, and includes pain relief,
bed rest, fluid replacement, and gradual convalescence. Acetaminophen rather
than aspirin is used for fever and pain relief. DHF and DSS are treated in
a hospital and patients monitored for shock, especially in the first 48 hours.
Patients with cyanosis or labored breathing should receive oxygen. Electrolytes
are replaced intravenously based on lab results to avoid over hydration and
congestive heart failure. Replacement of fluids is with half to full strength
normal saline in D5W at a rapid rate of 10-20 ml/kg/hour for 1-2 hours. In
severe cases of circulatory failure, volume expanders must be added. However,
the total fluid administration per day should not exceed the maintenance plus
5-10% of the deficit. Blood transfusions are based on H&H values. Packed
RBCs are transfused if there is a rapid drop in hematocrit. In cases of active
bleeding in vital organs, packed platelets are given in dosages of 0.2-0.4
U/kg of body weight. DHF and DSS are medical emergencies and should be treated
in intensive care settings. DHF results in death in 40-50% of untreated patients
who go into shock, but with intensive care the death rate drops to 2%. Children
under 15 years old are the most vulnerable (Chuansumrit et. al, 2000; Dung,
Day, Tam, Chau, Minh, Diet, Bethell, Kneen, Hien, White, & Farrar, 1999;
Ericsson, 2000; Tsai, 2000).
Prevention is imperative and accomplished by mosquito repellent, protective screens and clothing, and storing water in containers with lids. Public health measures such as community spraying and decreased vector reservoirs are critically important as the disease spreads.
Authors: Amy Roberts, FNP & Charles Kemp, FNP - Louise Herrington School of Nursing at Baylor University
References
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