Tuesday, June 18, 2019

Dengue

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.

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Dengue

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