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Dengue

Overview

Dengue is a common viral infection transmitted by the bite of an infected Aedes spp. mosquito. The virus is a member of the genus Flavivirus in the family Flaviviridae. Flavivirus species are also responsible for yellow fever, West Nile virus and Japanese encephalitis. The infection presents milder symptoms similar to influenza, along with extremely high fever and painful aching of the limbs and joints.

Dengue is widespread in tropical and sub-tropical regions, most commonly in central and South America, South East Asia and Western Pacific regions. It is non-endemic in the UK but cases have been reported due to travel to these affected areas. Between 2009 and 2013 there has been an average annual increase of reported Dengue fever in the UK by 53%, with 541 individual cases being confirmed in 2013. According to the World Health Organisation, there are 390 million Dengue infections per year, of which 96 million present with symptoms and 500000 with Dengue Haemorrhagic Shock.

 

Signs and symptoms

Symptoms develop after the incubation period of 10-14 days, usually within 4-7 days after exposure to the virus. Signs and symptoms include an abrupt high temperature of 40°C and a sudden onset of at least two of the following:

  • Severe headache (mostly in forehead)

  • Pain behind the eyes which worsens with eye movement

  • Muscle and joint pain occurring in the first few hours

  • Low back pain

  • Nausea or vomiting

  • Swollen lymph nodes in neck and groin

  • Fatigue

  • Skin rash which is characteristically bright red petechiae                                                                                                 (usually on lower limbs and chest)

  • Mild bleeding of the nose and gums

  • Easier bruising of body

 

Symptoms are usually self-limiting and will pass within a week. Alternatively, some patients, particularly those who have experienced previous infection, will develop a severe immunopathological response. This complication is known as Dengue Haemorrhagic Fever (DHF), also referred to as severe Dengue. Duration of DHF can last 7-10 days and has a mortality rate of less than 1% when treated. Without treatment, DHF has a mortality rate of 50%. The early symptoms are identical to the mild form of the disease. Severe symptoms present at defervescence, where viral load falls rapidly with reduced perfusion, central cyanosis, sweating and other signs of shock.

 

Signs and symptoms of DHF include:

  • Decrease in fever

  • Intense and persistent abdominal pain

  • Persistent vomiting with blood

  • Rapid breathing

  • Spontaneous bruising and bleeding from mucosal surfaces

  • Malaise

  • Encephalopathy

  • Hepatic failure

  • Renal failure

 

DHF can cause a sudden and severe drop in blood pressure, known as Dengue Shock Syndrome. Symptoms include:

  • Weak and rapid pulse

  • Rapid breathing

  • Cold clammy skin

  • Reduced urine outflow

  • Dry mouth

 

Causes

Dengue is transmitted by the bite of an Aedes aegypti or, less commonly,

Aedes albopictus mosquito which has been infected with the Flavivirus.

The virus disseminates in the blood of the bitten person within 2-3 days of

the infected bite.

Dengue infections can occur as a result of transmission of one of the four

serotypes: DEN-1, DEN-2, DEN-3 or DEN-4. Once infected with one

strain, lifelong immunity will be developed for that particular serotype.

Further infections from a different strain are possible so preventative

measures should still be followed. Further infections with a different

serotype can increase the risk of developing more serious complications

such as DHF. This increased risk disappears if infected with a third or fourth

strain.

 

Diagnosis and microbiological testing

Dengue fever is not easily distinguished from other causes of childhood febrile disease. In cases of DHF, signs and symptoms can resemble those of Yellow Fever.

 

Risk factors / at risk groups

Aedes mosquitos are commonly found near pools of stagnant water where they breed. Rates of Dengue are high in major cities of developing countries which have poor sanitation. Aedes mosquitoes feed in the day, most often early in the morning and again at dusk.

 

Treatment:

  • Antipyretics

  • Analgesics

  • Oral rehydration

 

Vaccines / preventative measures

There is currently no vaccine for dengue fever, so the best way to prevent catching the infection is to take common sense precautions when travelling in high-risk areas, such as:

  • Wearing loose fitting but protective clothing

  • Using a mosquito repellent throughout the day, especially around dawn and dusk – DEET

  • Sleeping under a mosquito net

  • Avoiding environments with stagnant water

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