“I came back from Thailand a few days ago with a high fever, splitting headache behind my eyes, and aching all over”

Fever in a RETURNING TRAVELLER demands a structured approach, and MALARIA must be excluded first as the must-not-miss — a single negative film does not exclude it, so three samples over 24–48 hours are needed (UK malaria treatment guidelines 2016), which means same-day hospital assessment. DENGUE (a mosquito-borne flavivirus common in SE Asia and the tropics, incubation usually <2 weeks) presents with high fever, severe RETRO-ORBITAL headache, marked MYALGIA/arthralgia ("breakbone fever"), rash, and often leucopenia and THROMBOCYTOPENIA, confirmed by RT-PCR/NS1 antigen early or serology later (UKHSA RIPL). Take a structured travel/exposure history (where, when, rural/urban, activities, bites, prophylaxis/vaccinations, food/water, freshwater swimming, sexual/animal exposure) and build the differential (malaria, dengue, typhoid, hepatitis A, rickettsia, leptospirosis, viral haemorrhagic fever in specific regions — isolate/notify, COVID), investigating with FBC, LFTs, U&E, blood films ×3, dengue NS1/serology and cultures while monitoring platelets/haematocrit. Critically, recognise dengue WARNING SIGNS of severe dengue needing admission (WHO 2009, international) — abdominal pain, persistent vomiting, fluid accumulation, mucosal bleeding/petechiae/bruising, lethargy/restlessness, liver enlargement, rising haematocrit with rapid platelet fall — most likely in the critical phase as the fever settles (often days 3–7); screen for sepsis (NICE NG253); and manage supportively with hydration, rest and PARACETAMOL while AVOIDING NSAIDs/aspirin (bleeding/platelet risk). Laboratories report confirmed dengue to UKHSA; clinicians notify suspected malaria or enteric fever. A second infection carries a higher risk of severe dengue (Qdenga for people aged 4 and over who have had dengue, Green Book chapter 15a). Safety-net robustly.