Tropical & Vector-Borne Critical Illness

• Acute undifferentiated fever in an endemic area is a bundle of treatable diseases — malaria, dengue, scrub typhus, leptospirosis, enteric fever and bacterial sepsis all look identical on day 3 and only diverge around day 6, by which time the treatable ones have already done their damage.
• Cover the lethal and treatable possibilities empirically while the tests come back: doxycycline for scrub typhus and leptospirosis, a β-lactam for bacterial sepsis, and IV artesunate whenever malaria is positive or cannot be excluded.
• Fluid strategy is disease-specific and this is where patients are lost: dengue needs the minimum that maintains perfusion with a hard stop once reabsorption starts, severe malaria and scrub typhus ARDS are made worse by over-filling, and leptospirosis with oliguric AKI usually needs early kidney replacement therapy.
• The free diagnoses are clinical — the scrub typhus eschar in the axilla, groin, under the breast or at the belt line; conjunctival suffusion and calf tenderness in leptospirosis; and the 20-minute whole-blood clotting test after snakebite — and each settles the question before any laboratory result arrives.
• Co-infection is common and one positive test does not close the case: repeat malaria films at 12 and 24 hours, reassess when the clinical course diverges from the parasite count, and think of tuberculosis in anyone whose illness is measured in weeks rather than days.

Acute Undifferentiated Fever in the Tropics: The First 6 Hours

• Fever of less than two weeks with no clear source in an endemic area → send in a single draw: malaria rapid test with thick and thin films, full blood count with platelets, dengue NS1 and IgM, leptospira and scrub typhus serology or PCR, two sets of blood cultures, urea, creatinine and electrolytes, liver enzymes, creatine kinase, lactate, coagulation screen, urinalysis and a chest radiograph
• Examine for the diagnoses that cost nothing to find: an eschar in the axilla, groin, under the breast or at the belt line (scrub typhus); conjunctival suffusion with calf tenderness (leptospirosis); a positive tourniquet test and haemorrhagic signs (dengue); jaundice with renal failure (leptospirosis, malaria or bacterial sepsis); and a bite mark
• Any organ dysfunction — shock, SpO₂ below 94% or respiratory distress, jaundice, oliguria or a rising creatinine, a falling GCS or seizure, bleeding, platelets below 50 × 10⁹/L, or lactate above 2 mmol/L?
• Severe
• Admit to ICU or HDU. Give IV artesunate if any malaria test is positive or malaria cannot be excluded in a high-transmission setting, and start doxycycline 100 mg 12-hourly to cover scrub typhus and leptospirosis — both are cheap, safe and lethal to miss. Azithromycin replaces doxycycline in pregnancy
• Add a β-lactam (ceftriaxone 2 g, or piperacillin-tazobactam where local resistance requires it) for bacterial sepsis after taking cultures, and follow the sepsis bundle. Resuscitate cautiously, because the right fluid strategy differs by disease and dengue in particular tolerates over-filling very badly
• Not severe
• Observe with a daily platelet count, haematocrit and clinical review. Warning signs typically appear on day 4–6 as the fever settles — which is exactly when patients are usually reassured and sent home
• Repeat malaria films at 12 and 24 hours before calling malaria excluded. A normal platelet count early does not exclude dengue, and serology taken in the first week is often negative — treat on the clinical picture and revise later.

Severe Dengue: Managing Fluid by Phase

• Stage the illness by phase rather than by calendar day: the febrile phase (days 1–3), the critical plasma-leak phase (days 4–6, as the fever falls), and the recovery or reabsorption phase (days 7–10). Almost every death happens in the critical phase, and the fever coming down is the warning, not the reassurance
• Look for warning signs at every review: abdominal pain or tenderness, persistent vomiting, clinical fluid accumulation (ascites or pleural effusion), mucosal bleeding, lethargy or restlessness, tender hepatomegaly greater than 2 cm, and a rising haematocrit with a simultaneously falling platelet count
• Shock — compensated (narrow pulse pressure of 20 mm Hg or less, tachycardia, cool peripheries, delayed capillary refill, with a normal systolic pressure) or decompensated?
• Shock
• Compensated shock → isotonic crystalloid 5–10 mL/kg over 1 hour, then reassess and step down through 5–7, 3–5 and 2–3 mL/kg/h as the haematocrit and perfusion improve. Decompensated shock → 20 mL/kg over 15–30 minutes, then step down the same way
• If the patient is not improving and the haematocrit is still high, give a colloid bolus. If the haematocrit has fallen while shock continues, the patient is bleeding — transfuse blood rather than giving more crystalloid
• Warning signs only
• Warning signs without shock → 5–7 mL/kg/h for 1–2 hours, then down to 3–5 and then 2–3 mL/kg/h, guided by a urine output of 0.5 mL/kg/h and serial haematocrit. Patients with no warning signs should drink; they do not need an intravenous line
• Give the minimum fluid that maintains perfusion for the 24–48 hours of leak, then stop. During reabsorption the leaked plasma returns to the circulation, and continuing the infusion produces pulmonary oedema — the commonest iatrogenic cause of death in dengue
• Do not transfuse platelets for a number alone; transfuse for clinically significant bleeding. Avoid NSAIDs, aspirin, corticosteroids and intramuscular injections, and use paracetamol for fever. Postpone any invasive procedure that can wait until the critical phase has passed.

Severe Malaria: Artesunate and the Complications

• Severe malaria is a positive test plus any one of: impaired consciousness or seizures, respiratory distress or acidosis, shock, pulmonary oedema, abnormal bleeding, jaundice with another organ dysfunction, haemoglobin below 7 g/dL, glucose below 2.2 mmol/L, creatinine above 265 µmol/L, or parasitaemia above 10%
• Give IV artesunate 2.4 mg/kg (3 mg/kg if under 20 kg) at 0, 12 and 24 hours and then daily. It is superior to quinine for survival and is first choice at every age and in every trimester of pregnancy. If artesunate is not immediately available, start artemether or quinine while it is obtained — never delay the first dose
• Switch to a full 3-day course of oral artemisinin-based combination therapy once the patient can swallow and has had at least 24 hours of parenteral treatment; a parenteral course on its own does not cure and invites recrudescence
• Treat the complications, which kill more often than the parasite does: check glucose every 4 hours (quinine causes hyperinsulinaemic hypoglycaemia), correct acidosis by restoring perfusion rather than with bicarbonate, be conservative with fluid because ARDS follows over-filling, transfuse for haemoglobin below 7 g/dL, and start kidney replacement therapy early for AKI
• Coma persisting, new seizures, or deterioration after the parasitaemia has cleared?
• Yes
• Exclude hypoglycaemia first, then bacterial meningitis and co-infecting bacterial sepsis, and consider post-artesunate delayed haemolysis — a falling haemoglobin 7–21 days after treatment that needs a repeat blood count and often transfusion. Do not give corticosteroids for cerebral malaria; they worsen the outcome
• No
• Monitor parasitaemia daily until it is negative, continue supportive care, and reassess the whole picture whenever the clinical course diverges from the parasite count
• Malaria and bacterial sepsis coexist often enough that empirical antibiotics are reasonable in severe malaria with shock, and co-infection with dengue or scrub typhus is common in the same season. A positive malaria test does not close the case.

Scrub Typhus, Leptospirosis and Other Treatable Zoonoses

• Treat first and confirm later. Serology is usually negative in the first week, so the decision to give doxycycline is a clinical one and the cost of waiting for a result is measured in organ failures
• Doxycycline 100 mg 12-hourly, intravenously or orally, for 7 days covers suspected scrub typhus, murine typhus, spotted fever and leptospirosis alike. Azithromycin 500 mg daily is the alternative in pregnancy and in children; in severe leptospirosis, IV penicillin G or ceftriaxone 2 g daily is equally acceptable. A short course of doxycycline is not contraindicated in children
• Search deliberately for the eschar. The painless black necrotic ulcer of scrub typhus hides in the axilla, groin, under the breast, at the waistband and behind the ear, and is found in fewer than half of cases unless the patient is fully undressed and examined in good light
• Organ dysfunction — ARDS, AKI, jaundice, myocarditis, meningoencephalitis or shock?
• Severe
• Support the failing organ: lung-protective ventilation for scrub typhus ARDS, which can progress within hours; kidney replacement therapy for the oliguric, hypokalaemic AKI of leptospirosis; and echocardiography for myocarditis. Pulmonary haemorrhage in leptospirosis is a specific and rapidly fatal presentation that needs early intubation and transfusion support
• Continue the antibiotic. Clinical improvement within 48 hours of starting doxycycline supports the diagnosis and is itself a useful diagnostic test
• Uncomplicated
• Expect defervescence within 48 hours. Failure to improve should send you back to the differential rather than up the antibiotic ladder
• Ask about the exposure — flood water, paddy fields, rodents, animal urine, scrub vegetation, occupation and recent travel — and then screen the household members or unit colleagues who shared it.

Snakebite: Clotting Test, Antivenom and Neurotoxicity

• First aid is immobilisation and rapid transport: splint the limb, keep it at heart level, and remove rings and tight clothing. Do not cut, suck, apply a tourniquet, use ice or give a traditional remedy — each adds injury without removing any venom
• Assess for envenoming rather than for the bite: swelling crossing a joint, tender draining lymph nodes, bleeding from gums, venepuncture sites or old wounds, ptosis, ophthalmoplegia, a broken-neck sign, dysphagia, dark urine and hypotension. A dry bite needs observation, not antivenom
• Do the 20-minute whole-blood clotting test at the bedside: 2 mL of fresh venous blood in a clean, dry glass tube, left undisturbed for 20 minutes. Blood that has not clotted means venom-induced consumption coagulopathy and is an indication for antivenom on its own. Repeat it 6-hourly
• Any sign of systemic envenoming — incoagulable blood, spontaneous bleeding, neurotoxicity, rhabdomyolysis, AKI, shock or rapidly advancing local swelling?
• Envenomed
• Give polyvalent antivenom by the local protocol as an IV infusion over 30–60 minutes, with adrenaline, oxygen and full resuscitation equipment at the bedside. Treat an anaphylactic reaction with adrenaline 0.5 mg IM at once, then restart the antivenom more slowly. The dose is identical for children and adults, because it neutralises venom rather than body weight
• Repeat the same dose after 6 hours if the clotting test is still abnormal, or after 1–2 hours if bleeding or neurotoxicity is progressing. Fresh frozen plasma and platelets are not a substitute — the coagulopathy recovers only once the venom is neutralised
• No systemic signs
• Observe for at least 24 hours with 6-hourly clotting tests and neurological checks before discharge. Krait bites can be painless and declare themselves hours later with paralysis, characteristically overnight
• Progressive neurotoxicity — ptosis, bulbar weakness, or a falling single-breath count or vital capacity?
• Yes
• Intubate early and electively rather than as a rescue; it is ventilation that keeps these patients alive while the antivenom works. Give a trial of neostigmine 0.5 mg with atropine 0.6 mg for post-synaptic (cobra-type) envenoming and continue it only if there is objective improvement — it does not work for pre-synaptic krait envenoming
• No
• Continue hourly neurological observation. The paralysis descends, so ptosis and ophthalmoplegia precede respiratory failure by hours and are the warning to act on
• Treat the limb conservatively: elevate it, mark the swelling, and do not perform a fasciotomy on swelling alone — measure the compartment pressure and correct the coagulopathy first. Give tetanus prophylaxis, and antibiotics only for an established infection.

Severe and Disseminated Tuberculosis in the ICU

• Consider tuberculosis in any critically ill patient with weeks of fever, weight loss, an unexplained infiltrate or miliary pattern, unexplained pancytopenia, adrenal insufficiency, lymphadenopathy, or a lymphocytic meningitis with low CSF glucose — particularly with HIV, diabetes, malnutrition, corticosteroid or biologic therapy
• Send rapid molecular testing (Xpert MTB/RIF Ultra) on sputum, tracheal aspirate, BAL, CSF, pleural or ascitic fluid or tissue: it answers within hours and reports rifampicin resistance at the same time. Add urine lipoarabinomannan in advanced HIV and mycobacterial blood cultures in disseminated disease, and send smear and culture on every available sample. Negative smears never exclude the diagnosis
• Start the four-drug regimen — isoniazid, rifampicin, pyrazinamide and ethambutol — without waiting for culture in a patient who is deteriorating. If enteral absorption is unreliable because of shock, ileus or vomiting, use the available parenteral agents (rifampicin, isoniazid, amikacin, a fluoroquinolone, linezolid) with specialist advice rather than leaving the patient untreated
• Tuberculous meningitis or pericarditis?
• Yes
• Add dexamethasone tapered over 6–8 weeks, extend treatment to 9–12 months for meningitis, and choose agents with good CSF penetration. Manage hydrocephalus and raised intracranial pressure actively — the decision about CSF diversion often determines the outcome
• No
• Treat for 6 months in drug-sensitive pulmonary disease and longer for bone and joint disease, notify the tuberculosis programme, and keep the patient isolated until infectiousness has been addressed
• In HIV co-infection, start antiretroviral therapy after 2 weeks of tuberculosis treatment when the CD4 count is below 50, and by 8 weeks otherwise. Expect paradoxical worsening from immune reconstitution and treat it with corticosteroids rather than by stopping tuberculosis treatment
• Drug hepatotoxicity is common in critical illness: check liver enzymes and bilirubin before and during treatment and have a written plan for stopping and sequentially reintroducing drugs. Isolate suspected pulmonary or laryngeal disease in a negative-pressure room and use fit-tested respirators, not surgical masks.