Dengue, diagnosis

• Clinical: biphasic flu-like syndrome with severe muscle pain and sometimes rash. Sometimes positive tourniquet (= Rumpel-Leede test) with DHF: petechiae appear after applying a sphygmomanometer to the upper arm. The sphygmomanometer is inflated to halfway between the systolic and diastolic blood pressure. The meter is left in place for 5 minutes. Afterwards one looks for petechiae in the crease of the elbow. If there are more than 20 in a 3 cm diameter circle, the test is positive. This indicates significant capillary fragility, thrombocytopenia or disturbed blood platelet function.

• Laboratory: thrombocytopenia and leukopenia; raised haematocrit due to haemoconcentration. This haemoconcentration is the result of a “capillary-leak” syndrome, with effusions in the pleura and/or ascites accompanied by hypoalbuminaemia (fluid loss from the blood circulation).

• Serology: retrospectively, serological determination of antibodies is possible. There is considerable cross-reaction between the different dengue viruses. An important new development is the dengue ICT test. With this, both the IgM and IgG antibodies can be detected very quickly (in a few minutes). The test is however quite expensive. Its reliability needs to be tested further, but ELISA is probably better. Flaviviruses share antigenic epitopes, which elicit cross-reacting antibodies. These cross-reactive responses can confound the interpretation of serological tests, and it is often impossible to determine with certainty the infecting virus without resorting to performing neutralization tests.

• Antigen detection. A dengue antigen detection assay is also available. This will be positive during the early viraemic phase.

Category: Medicine Notes