Question
A 25-year-old migrant labourer was brought to outpatient department with high grade fever, severe myalgia and retro orbital pain. On examination, he had maculopapular rashes over his body. Blood examination showed thrombocytopenia and NS1 antigen positive
- (a) What is the probable diagnosis and name the aetiological agent 2 mark(s)
- (b) Write the vector transmitting the agent 1 mark(s)
- (c) Write four differential diagnosis of the condition 2 mark(s)
- (d) Write briefly the pathogenesis of the disease e) Write two complications of the condition f) How will you diagnose the infection in the lab g) Mention the preventive measures. 3 mark(s)
Answer
a) Probable diagnosis and aetiological agent: Dengue fever — high-grade fever, severe myalgia, retro-orbital pain, maculopapular rash, thrombocytopenia, and positive NS1 antigen is classical. Aetiological agent: Dengue virus (a Flavivirus, four serotypes DENV-1–4).
b) Vector: Aedes aegypti mosquito (a day-biting mosquito; Aedes albopictus is a secondary vector).
c) Four differential diagnoses: Chikungunya, malaria, leptospirosis, and enteric (typhoid) fever — all can present with fever, myalgia, and non-specific systemic symptoms in a similar epidemiological setting.
d) Pathogenesis After the mosquito bite, the virus replicates in local dendritic cells and disseminates via lymphatics/blood to the reticuloendothelial system, producing viraemia and a cytokine response responsible for fever, myalgia, and rash. In 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 replication and drive a cytokine storm, increasing capillary permeability (plasma leakage) and suppressing bone marrow (thrombocytopenia).
e) Two complications: Dengue Haemorrhagic Fever (DHF) and Dengue Shock Syndrome (DSS).
f) Laboratory diagnosis: NS1 antigen (early, positive here); IgM ELISA (from ~day 5); RT-PCR (early viraemic phase, allows serotyping); full blood count (thrombocytopenia, rising haematocrit).
g) 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 — particularly relevant here given the patient’s occupational/migrant-labourer exposure to potential vector-breeding construction sites.