Introduction

Dengue fever is a viral infection transmitted to humans by the bite of a female Aedes mosquito. The global incidence of dengue fever is increasing to the extent that the World Health Organisation (WHO) recognises dengue as a “major and emergent concern” because of its expanding distribution and increased frequency of epidemics.

Dengue fever predominately occurs in urban or semi-urban areas in tropical and sub-tropical climates.

Dengue fever is most commonly found in:

  • South East Asia
  • The Indian subcontinent
  • Southern and Central America
  • The Caribbean
  • Africa
  • Australia
  • The Pacific Islands

A recent estimate of the global incidence of Dengue indicates 390 million dengue infections per year, of these 96 million show clinical symptoms. The incidence of the infection has grown dramatically in recent years with up to 50% of the world’s population now being at risk. (Ref WHO factsheet)

Transmission

Dengue fever is spread by the bite of the female Aedes mosquito. The Aedes mosquito is also responsible for the transmission of other viral infections including Zika, Chikungunya and yellow fever.

Transmission of dengue fever occurs where an infected human is bitten by a mosquito and the mosquito then bites another human. Whilst infected humans are the main reservoir of the virus human to human transmission is not possible.

The Aedes mosquito feeds during the day preferring to feed early morning or late afternoon. The infected mosquito is a slow feeder and is easily disturbed during feeding. Once disturbed they tend to return to the same subject to continue feeding or move to others to complete a meal. This potentially can result in several people being infected during a single mosquito meal.

Dengue fever is caused by a flavivirus. Four different serotypes can cause dengue fever, DEN1, DEN2, DEN3 and DEN4. Infection by one serotype will provide lifelong immunity to that specific serotype but infection with the other serotypes is still possible and may result in more severe symptoms.

The Aedes mosquito most commonly implicated in spreading dengue fever is Aedes aegypti, although the infection can be spread by Aedes Albopictus. The latter is highly adaptable being able to survive at cooler temperatures, hibernate and find shelter. This ability to survive at lower temperatures has assisted the spread of dengue fever into cooler geographic areas such as Europe and Northern America.  

In the last 50 years dengue has spread from affecting a small number of countries to being endemic in 128 countries. This rapid spread of the virus can be attributed to increasing population size, urban living, poor public hygiene, rapid urbanisation, increased international trade and global travel.

The female Aedes mosquito lays its eggs in man-made pools or water containers. The increasing global trade in worn tyres has facilitated the spread of the infection as worn tyres collect water providing a breeding ground for the female mosquito.

 Signs and symptoms

The classic symptoms of dengue fever are fever, malaise and fatigue. Dengue fever should be considered in any patient complaining of fever who has recently returned from travelling to geographical areas where dengue fever is endemic. The incubation period of dengue fever is 4-7 days (range 3-14) consequently patients starting with symptoms more than 14 days after return are unlikely to be suffering from dengue fever.

Dengue fever should be suspected when a patient presents with a high fever (over 40˚C) accompanied by 2 of the following symptoms:

  • Severe headache
  • Pain behind the eyes
  • Severe muscle and joint pains- hence the name “break bone” fever
  • Nausea and vomiting
  • Swollen glands
  • Maculopapular rash

 Symptoms generally last for between 2-7 days.

Recovery from dengue fever can be associated with prolonged fatigue although the vast majority of patients will make a full recovery with no long term consequences.

Complications

Complications associated with dengue fever include severe dengue fever and dengue shock syndrome.

Severe dengue fever is a potentially fatal complication of dengue fever that occurs in approximately 1-2% of cases. The key symptom associated with severe dengue is bleeding that leads to compromised function of major organs leading to the development of bradycardia, respiratory distress, renal failure, impaired consciousness and potentially death where medical treatment is not readily available.

 Health professionals involved in the treatment of patients with dengue fever should be alert to the warning signs for the development of severe dengue, these typically start 3-7 days after the original symptoms, and include:

  • Rapid breathing
  • Decreasing fever
  • Abdominal pain
  • Fatigue or lethargy
  • Bleeding gums.

Severe dengue is rarely seen in travellers, it is most commonly seen in children in endemic areas particularly those who have previously been infected with dengue fever. Initial infection provides lifelong immunity to the infecting serotype, but subsequent infection with the other serotypes is associated with an increased risk of developing severe dengue.

Travellers who frequently visit areas where dengue is endemic could be at an increased risk of contracting severe dengue fever although this has not been demonstrated clinically.

Dengue shock syndrome is caused by increased vascular permeability and movement of fluid into the extravascular space; this can cause a dramatic drop in blood pressure or dengue shock syndrome (DSS).

 Classic symptoms of DSS include:

  • Dry mouth
  • Fast breathing
  • Reduced urine flow
  • Cold clammy skin
  • Weak rapid pulse

Treatment results in rapid recovery for the vast majority of sufferers but without treatment it can be fatal in up to 40% of cases.

Prevention

There is currently no dengue fever vaccine available within the UK. Dengvaxia is the first vaccine licensed in the world to prevent dengue fever. It has been granted a marketing authorisation in Mexico, the Philippines and Brazil.

Dengvaxia is a live, recombinant tetravalent vaccine for use in people aged 9-45 years who live in endemic areas.

Clinical trials of the vaccine have shown that it is effective against all four dengue serotypes; protecting 66% of those vaccinated, and in the most severe form of the disease was effective in 93% of cases. The vaccine was shown to reduce hospitalisation from dengue by 80%.

Bite avoidance is the most important action that travellers can take to reduce their risk of contracting dengue fever.

Appropriate bite avoidance measures would include:

  • Using insect repellent containing N-diethyltoluamide (DEET) for all travellers over the age of 2 months. DEET is safe for use in pregnant travellers. Icaridin is an alternate insect repellent reported to have insect repellent properties equivalent to DEET.
  • Wearing light coloured, long sleeved, loose clothing.
  • Being aware of the environment and avoiding areas where mosquitoes will breed such as areas with standing water or water containers.
  • Longer-stay travellers are advised to clear any potential breeding grounds from around their accommodation, where possible.
  • Mosquito nets will help to prevent bites whilst asleep. The Aedes mosquito tends to bite early morning and late afternoon so the impact of this in reducing dengue fever is questionable although it will help to reduce transmission of other mosquito borne infection.
Treatment

There is no specific treatment for dengue fever; treatment is symptomatic focusing on rehydration and pain relief.

Paracetamol can be used to control the fever and alleviate pain whilst intravenous fluids are used to rehydrate the patient.

Patients with dengue fever should not be recommended aspirin or other anti-inflammatory agents as these can increase the risk of haemorrhagic complications.

Conclusion

Pharmacists are ideally placed to advise patients of the possible risks of infection whilst travelling abroad, including Dengue fever. For a detailed account of travel risk assessment read our Pharmacy Excellence module on the Numark + training library http://learning.numarknet.com/travel-risk-assessment-16 . An awareness of the specific risks for individual patients and areas of the world ensures that pharmacists are able to provide accurate, timely and up to date information