Dengue fever

*The World Health Organization (WHO) has stated "Dengue is one disease entity with different clinical presentations and often with unpredictable clinical evolution and outcome"

*Dengue virus is transmitted by the bite of an infected Aedes mosquito and is endemic in tropical and subtropical regions throughout the world. The female Ae. aegypti (the most important vector) mosquito is semi-domesticated, preferring to lay its eggs in man-made water containers, resting indoors and feeding in the early morning or late afternoon (unlike the malaria mosquito). Anti-malarial measures are largely ineffective against dengue.

*Patients become infected once bitten by mosquitoes. The virus passes to lymph nodes and replicates, which is followed by spread to the circulation and other tissues. Incubation period is 2-7 days.

SymptomsHaemorrhagic fever syndromes begin with abrupt onset of fever and myalgia.

Fever is associated with frontal or retro-orbital headache accompanied by onset of a generalised rash.

Symptoms regress for a day or two but may recur, although fever is rarely as high as at the onset.

Dengue fever cases experience severe bony and myalgic pain in legs, joints and lower back which may last for weeks (hence, breakbone fever).

Nausea, vomiting, cutaneous hyperaesthesia, taste disturbance and anorexia are common.

Abdominal pain may occur and, if severe, suggests possible DHF.

*Signs*High fever - usually between 39.5-41°C - persisting for 1-7 days only.

Fever is often biphasic with two peaks. Sudden disappearance of fever can be a warning signal of DHF.

*Cardiovascular signs include hypotension and narrow pulse pressure, poor capillary refill and relative bradycardia.

*Rash is initially generalised, macular and blanching and fades after 1-2 days; it may then reappear as a maculopapular, morbilliform rash with sparing of palms and soles. Desquamation may follow.

* Tender muscles on palpation.* There may be hepatomegaly and lymphadenopathy.* Positive tourniquet test. This can be performed by inflating a blood

pressure cuff on the upper arm to a pressure midway between the systolic and diastolic pressures for five minutes. A test is considered positive when ≥20 petechiae per 2.5 cm2 are seen. It can be negative or just mildly positive during profound shock.

*Other haemorrhagic manifestations include spontaneous petechiae (best visualised in the axillae), purpura, epistaxis, gum bleeding, gastrointestinal haemorrhage and menorrhagia.

*With DHF, there may be pleural effusion, ascites and pericarditis due to plasma leakage.

* Periorbital oedema and proteinuria may be present.

*Differential diagnosis*Malaria

*Typhoid fever

*HIV seroconversion

*Infectious mononucleosis

*Coxsackie and other enteroviruses

*Rickettsial infections

*Measles

*Rubella

*Parvovirus B19

*Weil's disease (leptospirosis)

*Influenza

*Scrub typhus

*Chikungunya viral infections

*InvestigationsInvestigations*FBC may show high packed cell volume if

haemoconcentrated and low platelets. There may be a paradoxical lymphocytosis (>15% circulating white cells) in context of overall leukopenia.*Clotting studies can reveal prolongation of APTT and PT.

Fibrin degradation products may be elevated.*U&E may show electrolyte disturbance and LFTs can be

elevated - especially AST.*Severe cases may show reduced venous bicarbonate due to

acidosis.*Infection may be confirmed by isolation of virus in serum

and detection of IgM and IgG antibodies by ELISA, monoclonal antibody or haemagglutination. PCR-based techniques are increasingly being used.*X-rays are often used to exclude other sources of

sepsis/assess complications, although in dengue infection the CXR may show abnormalities, such as pleural effusion, in the first week.[15]*Blood cultures and repeated malaria films should be

checked in the traveller returning with a high fever.

*Management *Fever control with paracetamol, tepid sponging and fans.

*Intravenous fluid resuscitation with close monitoring, remembering the risk of increased capillary permeability. Monitor CVP and urine output and pay close attention to electrolytes, packed cell volume, platelets and LFTs. High volume and aggressive colloid/crystalloid infusion under expert guidance may be needed. Inotropes may also be required, as may renal support.

*Secondary bacterial infections may occur and require treatment.

*Haemorrhage and shock will require FFP and platelets.

*Those with DHF/DSS are likely to require intensive care, where available.