Question
A 24 year old male presented with fever, headache, severe myalgia, retrobulbar pain for past five days. On examination, he had maculopapular rash all over his body. Blood examination revealed thrombocytopenia
- (a) What is the most probable diagnosis. 1 mark(s)
- (b) Name the etiological agent and vector 2 mark(s)
- (c) Write briefly about the pathogenesis of this disease 2 mark(s)
- (d) Write TWO complications of the condition e) Describe the laboratory diagnosis f) Mention the preventive measures 2 mark(s)
Answer
a) Most probable diagnosis: Dengue fever — fever, severe myalgia, retro-orbital pain (“breakbone fever”), maculopapular rash, and thrombocytopenia over five days is classical.
b) Etiological agent and vector: Dengue virus (a Flavivirus, four serotypes DENV-1–4); vector: Aedes aegypti mosquito (a day-biting mosquito; Aedes albopictus is a secondary vector).
c) Pathogenesis After the bite of an infective Aedes mosquito, the virus replicates in local dendritic cells and disseminates via lymphatics/blood to the reticuloendothelial system (liver, spleen, bone marrow), producing viraemia. The host immune response (cytokine release — TNF-α and others) drives fever, myalgia, and the rash; in a secondary infection with a different serotype, Antibody-Dependent Enhancement (ADE) — pre-existing non-neutralizing cross-reactive antibody enhances viral uptake into Fc-receptor-bearing monocytes/macrophages — can amplify viral replication and drive a more severe cytokine storm, increasing capillary permeability and predisposing to dengue haemorrhagic fever.
d) Two complications: Dengue Haemorrhagic Fever (DHF) — thrombocytopenia and plasma leakage; Dengue Shock Syndrome (DSS) — severe plasma leakage causing circulatory failure/shock.
e) Laboratory diagnosis
- NS1 antigen — detectable from day 1, before antibody develops.
- IgM ELISA — positive from about day 5.
- RT-PCR — detects viral RNA in the early viraemic phase, allows serotyping.
- Full blood count — thrombocytopenia and rising haematocrit (haemoconcentration).
f) Preventive measures: mosquito control (source reduction, larvicides, insecticide spraying); personal protective measures (repellents, protective clothing, bed nets); community health education; dengue vaccination where available for select endemic populations.