Dengue

Epidemiology of Infectious Diseases: Dengue

Causal agent
Dengue fever and dengue haemorrhagic (DHF) fever are caused by a flavivirus with 4 distinct serogroups (DEN- 1, DEN-2, DEN-3 and DEN-4). 

Infection with 1 serogroup confers life long immunity, but provides only partial and transient protection against infection by the other 3 serogroups. Sequential infection increases the risk of more serious disease resulting in DHF.

Common clinical features

  • Dengue fever is characterised by the sudden onset of fever, severe frontal headache, joint and muscle pain, myalgia, anorexia, nausea, vomiting and rash (appearing 3-5 days after onset of fever).
  • Infants and children may have a non-specific febrile illness with rash.
  • DHF - is a potentially life threatening complication that is characterised by high fever, haemorrhagic phenomena - often with enlargement of the liver and in severe cases, circulatory failure1.
  • DHF occurs principally in children but also occurs in adults.

Epidemiology

  • Endemic in most countries in the tropics.
  • Global prevalence has increased dramatically in the last 25 years and the WHO estimates that there may be 50 million cases of dengue infection worldwide each year2.
  • The reasons for this increase are complex and not well understood. However, several important factors have been identified including:  uncontrolled urbanization and population growth especially in South east Asia where substandard water and waste management provide a perfect environment for the Aedes mosquito to breed. Other factors include the failure of public health infrastructure to provide effective or sustained vector control programmes.
  • According the WHO dengue is now endemic in > 100 countries in Africa, the Americas, The Eastern Mediterranean, South East Asia and the Western Pacific. An estimated 2.5 billion people live in areas where dengue viruses are transmitted.
  • The highest burden of disease occurs in South East Asia and the Western Pacific but it is increasingly becoming an important public health problem in South America and the Caribbean2.
  • Epidemics caused by all four virus serotypes have become more frequent and larger in the last 25 years, with major epidemics occurring in many countries every 3-5 years.
  • In the Americas the first major epidemic started in 1981. The peak in 1982 resulted from an explosive outbreak that started in Cuba resulting in over 300,000 cases of dengue fever, 10,000 cases of DHF and 158 deaths. Subsequent epidemics have been reported in 1998 and 2002.
  • Almost half the dengue imported into Europe comes from Asia.

Reservoir
Aedes mosquito.  

The Aedes mosquitoes commonly breed in water filled receptacles (discarded tyres, buckets, cans and cisterns) close to human habitation.

Mode of transmission

  • Through the bite of an infected female Aedes mosquito.
  • The Aedes aegypti, a domestic day biting mosquito is the principal vector for dengue transmission.
  • However, geographical variation in vectors occurs and in recent years, Aedes albopictus, a secondary dengue vector in Asia has become established in the United States, several Latin American and Caribbean countries.
  • The Aedes mosquito are most active during daylight hours, with two peak periods of biting activity (in the morning for several hours after daybreak and for several hours before dark).
  • Primates may also act as a reservoir for the virus in the forests of South East Asia and western Africa1.

Incubation period
3-14 days, commonly 4-7 days.

Period of Communicability

  • No direct person to person spread.
  • Patients are infective for mosquitoes from shortly before and during the febrile period.
  • The mosquito becomes infective 8-12 days following the blood-meals and remains infective for life (2-3 months)1. 

Prevention and control

  • No vaccine, chemoprophylaxis or specific treatment is currently available for dengue and DHF.
  • Appropriate clinical management of cases significantly reduces mortality of infected persons.
  • Effective vector control in endemic areas.
  • Advice to travellers from the UK to countries where dengue is endemic or areas with outbreaks is avoidance of mosquito bites.

References

  1. Heymann D L, editor, Control of Communicable Disease Manual. 18th ed. American Public Health Association; 2004.
     
  2. Hawker J, Begg N, Blair I, Reintjes R, Weinberg J. Communicable Disease Control Handbook, Blackwell, 2005.

© CM Kirwan 2006