Dengue fever

From Ganfyd

"Breakbone fever", from the intensity of the rigors

Aetiology

Dengue fever is caused by a flavivirus, transmitted by the Aedes aegypti mosquito (hence an arbovirus). It is an enveloped RNA virus. There are 4 serotypes of dengue virus.

Epidemiology

Dengue fever has become a global pandemic over recent decades. Each year, an estimated 100 million cases of dengue fever and several hundred thousand cases of DHF occur (depending on epidemics). Widespread in tropical regions, particularly of Asia & Americas, not so much in Africa. Travellers to Dengue affected regions are at risk and Dengue should be considered in returning travellers with the appropriate clinical picture.

Transmission

The Dengue fever virus is probably the most important of the arboviruses in terms of cases and deaths. The vector is the Aedes mosquito, which has spread globally due to its ability to breed in domestic habitats eg small water containers, and increased urbanization.

Clinical Features

Dengue can present with anything from a minor febrile illness to fatal haemorrhagic disease. The presentation is not related to the serotype. In endemic areas, infection usually produces a mild disease especially in children. Classic Dengue fever usually affects older children and adults, and causes sudden onset fever, headache, muscle pains. Incubation period is typically 4-7 days. A rash may be present, which may develop into petechiae, and eventually desquamates.

Haemorrhagic manifestations e.g. epistaxis, purpura, GI haemorrhage may be seen, but the illness is usually self-limiting and rarely fatal. Other features are neutropenia, atypical lymphocytosis, thrombocytopenia and mild elevations of transaminases.

Dengue Haemorrhagic Fever (DHF) primarily affects children. Initial presentation is similar to that of classic dengue fever, but at the time of defervescence (or shortly before) vascular leak develops causing shock (often with abdominal pain) then haemorrhage in skin, GI tract and at venepuncture sites. Besides thrombocytopenia and haemoconcentration, a tourniquet test (demonstrating capillary fragility) may help diagnosis. If shock is appropriately managed and the patient survives the first 24 hours then recovery is usually quick and uneventful^[1].

Pathogenesis

DHF is believed to be an antibody-dependent enhancement phenomenon. The patient must first have antibodies to Dengue, through previous exposure. On second exposure, but with a different serotype, antigen-antibody complexes form that are taken up by macrophages, but that are not effectively neutralized; instead, replication continues and inflammatory mediators are produced causing vascular leak etc.

Investigations

FBC, LFTS, Dengue serology.

Treatment

Supportive - usually with crystalloid +/- colloid resuscitation. The morbidity and mortality associated with DHF is significant, especially where patients do not have access to ITU/HDU facilities.

Prevention

The development of a vaccine is a priority, but faces the problem of increasing the risk of DHF through immune enhancement. A tetravalent vaccine would be required.

It is possible that Wolbachia pipientis may help provide control by reducing mosquito infectivity^[2].

Notifiable in the UK.

References