Dengue
is a mosquito-borne tropical disease caused by
the dengue virus (DENV). The virus has four serotypes DENV-1 to DENV4. Infection with one serotype usually gives lifelong immunity to that serotype,
but only short-term immunity to the others.
Causative agents:
Dengue virus is an RNA virus of the family Flaviviridae.
Host factor:
Humans are the primary host of the virus but it also circulates in
nonhuman primates. Severe disease is more common in extreme of ages,
female sex, high body mass index, high viral load, reinfection with another
serotype and presence of chronic diseases such as diabetes, sickle cell
and asthma.
Environmental factor:
An Aedes mosquito is the vector. Aedes aegypti is particularly involved in transmission, as it prefers to lay its eggs in artificial
water containers, to live in close proximity to humans, and to feed on people
rather than other vertebrates. An infection can be acquired via a single bite.
Aedes prefer to bite more than one site before it completes its meal. The
mosquito prefers to bite during dusk and dawn. Monsoons and hot climate
increases the breeding of mosquito hence the incidence rate increases with it.
Mode of transmission, Incubation period, Period of communicability:
A
female mosquito that takes a blood meal from a person infected with dengue
fever, during the initial 2–10 day febrile period, becomes itself infected with
the virus in the cells lining its gut. About 8–10 days later, the virus spreads to
other tissues including the mosquito's salivary glands and is subsequently
released into its saliva. Cases of vertical transmission and contaminated blood
product consumption related transmission have been reported. Incubation
period is less than two weeks.
Clinical features:
Dengue presents in two forms; Dengue fever and Severe Dengue.
Dengue fever presents as high grade fever, headache especially retro orbital
pain, and rashes (triad of dengue). It may be associated with muscle,
abdomen, bone and joint pain. Children usually presents with vomiting,
diarrhoea and dehydration whereas adults usually presents with bleeding
manifestation. Febrile phase may last for seven days however patient may
remain afebrile for a few days after initial few days fever.
Severe dengue manifest as bleeding and/or fluid loss in third space leading to
hypovolumic shock. Any of the warning signs (Mucosal bleeding, Worsening
abdominal pain, Ongoing vomiting, Liver enlargement, High hematocrit with
low platelets, Lethargy or restlessness, Serosal effusions and Shock) during first
week of fever needs scrutiny for Severe Dengue.
Complications of Dengue
are Myocarditis, Transverse myelitis, Guillain Barre
Syndrome, Acute liver failure, Encephalitis and DIC but rare.
Diagnosis
Laboratory finding suggestive of dengue are Leucopenia, Atypical
lymphocytsis, Thrombocytopenia, Hemoconcentration, raised ESR, LDH, urea
and liver enzymes (ALT>AST).
Honeycomb sign in USG is specific findings.
Antigen detection test NS1 remains positive from day of fever to first week.
Antibodies (IgG/IgM) are positive at the end of first week to first few months.
Molecular technique PCR can be done during the period of positivity of NS1
antigen test.
Case definition
Suspected case:
An acute febrile case with any of above clinical presentation
from tropics or with travel history within a last two weeks.
Definite cases:
Clinical suspicion with positive antigen detection test (NS1) or
PCR or four fold rise in IgM/IgG titer.
Severe dengue:
Definite dengue case with any one of the warning signs
(Mucosal bleeding, Worsening abdominal pain, Ongoing vomiting, Liver
enlargement, High hematocrit with low platelets, Lethargy or restlessness, Serosal effusions, Shock)
Management of
patient
Dengue fever:
There is no specific medication for treatment of a dengue
infection. Avoid NSAIDS, steroids and antibiotics. Encourage patient to drink
plenty of fluids. Paracetamol and cold sponging is recommended for fever.
Severe dengue: Patient needs admission. Fluid management is crucial to save
life. The rate of fluid administration is titrated to a urinary output of 0.5–
1 mL/kg/h, stable vital signs and normalization of hematocrit. Platelets
transfusion is indicated if there is ongoing spontaneous bleeding or very
severe thrombocytopenia.
Prevention and
control
measures
Prevention of mosquito bites between dusk and dawn is the first line of
defense against malaria. Measures to prevent mosquito bites include sleeping
under long-lasting insecticidal nets, and using protective clothing and insect
repellents.
Dengvaxia is one of the most popular vaccines of dengue being
approved and reviewed by around 20 countries in Asia and Latin America.
Special
considerations
Dengue fever is not life threatening however severe dengue if not supported
with treatment is highly fatal.
