Haematology Vignettes – 18

Suggestive but not diagnostic of dengue fever

A 62-year-old male returning from Fiji presents with fever, severe headache and myalgia. He is clinically very unwell and is admitted to intensive care.

A full blood count is performed. The patient is severely pancytopenic:
Hb 110 g/L, WBC 0.43 x 109/L and Platelet count 14 x 109/L.

Renal function and liver function tests are also performed:

Urea 21.2 mmol/L and Creatinine 492 umol/L

GGT 121 U/L, AST 249 U/L and ALT 95 U/L

The patient also has acute renal failure and abnormal liver function tests.

The blood film shows the presence of ‘Turk’ cells as well as a left shift with toxic changes. As the differential diagnosis for this patient is malaria, a malaria screen is performed. The result is negative.

Pancytopenia and the presence of ‘Turk’ cells on the blood film are also suggestive of dengue fever. Serology for dengue fever is performed:

IgG antibody is negative while IgM antibody is positive.

A diagnosis of dengue haemorrhagic fever is made.

This patient died three days after admission to intensive care.

Peripheral blood film showing 'Turk' cells.

Peripheral blood film showing ‘Turk’ cells.

Dengue fever and dengue haemorrhagic fevers are acute febrile diseases found in the tropics and Africa with a geographical spread similar to that of malaria. One major difference is that while malaria is not found in major cities, dengue occurs in developed tropical nations including Singapore, Taiwan, Fiji, Indonesia and Brazil. It is also found in northern Australia.

Any one of four closely related virus serotypes of the genus Flavivirus, family Flaviviridae, causes dengue fever.

Dengue fever is transmitted to humans by the Aedes Aegypti mosquito.

The clinical features of dengue are a sudden onset of fever, severe headache, muscle and joint pain and a petechial rash on the lower limbs and chest. There may also be gastritis with abdominal pain, nausea, vomiting and diarrhoea.

The fever lasts about six to seven days. The platelet count steadily drops during the period of fever. The platelet count returns to normal as the temperature returns to normal.

Treatment is supportive therapy. A platelet transfusion is indicated if the platelet count drops significantly as is a blood transfusion if the haemoglobin is low secondary to malaena indicative of gastrointestinal bleeding.

Dengue fever is the most important mosquito-borne disease affecting humans after malaria. Some forty million cases of dengue fever and several hundred thousand cases of dengue haemorrhagic fever are reported every year.

Although dengue fever is not diagnostic from the blood film, a rapidly progressive thrombocytopenia together with the presence of ‘Turk’ cells is highly suggestive of the viral infection.