Dengue Fever

Also known as: Dengue

Acute febrile illness caused by dengue virus (DENV, family Flaviviridae, 4 serotypes DENV-1–4), transmitted by Aedes aegypti (and Aedes albopictus) mosquitoes. Infection with one serotype confers lifelong immunity to that serotype but only transient cross-protection to others; secondary infection with a different serotype carries higher risk of severe dengue (antibody-dependent enhancement).

Classified by WHO 2009 criteria:

Dengue without warning signs
Dengue with warning signs: abdominal pain, persistent vomiting, fluid accumulation (ascites, pleural effusion), mucosal bleeding, lethargy/restlessness, liver enlargement >2cm, rising hematocrit with rapid platelet drop
Severe dengue: severe plasma leakage (shock, fluid accumulation with respiratory distress), severe bleeding, or severe organ impairment (liver, CNS, heart)

Phases of illness: febrile phase (days 1–3) → critical phase (days 4–6, plasma leakage risk) → recovery phase (days 7+, fluid reabsorption).

Febrile phase: sudden high fever (39–40°C), severe headache, retro-orbital pain, myalgia, arthralgia ("breakbone fever"), maculopapular/morbilliform rash, mild hemorrhagic manifestations (petechiae, positive tourniquet test), nausea/vomiting, facial flushing
Critical phase (around defervescence, days 4–6 — the dangerous transition): temperature drops but this does NOT mean improvement — plasma leakage begins here
Warning signs (monitor closely, admit if present): abdominal pain/tenderness, persistent vomiting, clinical fluid accumulation, mucosal bleeding, lethargy/restlessness, liver enlargement, rising hematocrit concurrent with rapid platelet decline
Progression to severe dengue: narrow pulse pressure (<20mmHg), tachycardia, cold clammy extremities, delayed capillary refill (signs of dengue shock syndrome), significant bleeding (GI, vaginal, intracranial), organ impairment (AST/ALT ≥1000, impaired consciousness, cardiac involvement)
Recovery phase: gradual reabsorption of extravasated fluid, improved appetite, bradycardia, characteristic convalescent rash ("isles of white in a sea of red")
Red flags for shock: restlessness/irritability progressing to lethargy, cold extremities, prolonged capillary refill >2sec, weak/rapid pulse, narrowing pulse pressure — precede hypotension, which is a LATE sign

Clinical suspicion: acute febrile illness + 2 of (nausea/vomiting, rash, aches/pains, positive tourniquet test, leukopenia, warning signs) in endemic area/exposure
FBC: leukopenia, thrombocytopenia (progressive fall, nadir typically around critical phase), rising hematocrit (hemoconcentration — indicates plasma leakage; a 20% rise from baseline is significant)
NS1 antigen: positive from day 1–7 of fever (early detection)
IgM/IgG serology: IgM detectable from day 5 onward (acute infection); IgG rise in secondary infection (paired sera useful)
PCR: confirms serotype, most sensitive in first 5 days
LFTs: transaminitis common; AST/ALT elevation
Coagulation profile if bleeding/severe disease: prolonged PT/APTT, low fibrinogen in severe cases
Serial hematocrit and platelet monitoring — essential for detecting critical phase transition
Ultrasound/CXR: detect subclinical plasma leakage (pleural effusion, ascites, gallbladder wall thickening) — useful in risk-stratifying warning-sign patients

Differentials: malaria (always test/exclude in endemic overlap areas), chikungunya, zika, typhoid, leptospirosis, measles, rubella, other viral hemorrhagic fevers, influenza.

No specific antiviral; management is supportive, centered on careful fluid management and monitoring for plasma leakage/shock.

Dengue without warning signs (outpatient management):

Adequate oral fluid intake (oral rehydration solution, fruit juice, avoid excessive plain water)
Paracetamol for fever/pain — strictly avoid NSAIDs (ibuprofen, aspirin, diclofenac) and other salicylates — bleeding risk and Reye's syndrome
Daily review: temperature, fluid intake/output, warning signs, FBC (hematocrit, platelets)
Educate on warning signs requiring immediate return

Dengue with warning signs (admit for monitoring):

IV isotonic crystalloids (normal saline or Ringer's lactate) starting at 5–7mL/kg/hour, titrate based on clinical response, hematocrit, urine output
Monitor vitals, urine output, hematocrit every 4–6 hours during critical phase
Reduce IV rate as patient stabilizes/enters recovery phase (risk of fluid overload once leakage resolves — this is a common cause of iatrogenic harm if fluids not tapered)

Severe dengue/dengue shock syndrome (ICU-level care):

Aggressive fluid resuscitation: IV crystalloid bolus 10–20mL/kg over 1 hour, reassess; consider colloids (e.g., dextran) if repeated boluses fail
Blood transfusion if significant hemorrhage (whole blood or packed cells); platelet transfusion NOT routinely indicated for thrombocytopenia alone without active bleeding — even very low counts (<10,000-20,000) are managed expectantly unless bleeding present
Correct hypoglycemia, electrolyte imbalances, metabolic acidosis
Manage organ-specific complications (hepatic failure, encephalopathy, myocarditis) supportively
Avoid IM injections and unnecessary invasive procedures (bleeding risk)

Discharge criteria: afebrile ≥24 hours without antipyretics, improved appetite, stable hematocrit, platelet count rising (>50,000), no respiratory distress, adequate urine output.

Prevention: vector control (eliminate breeding sites, insecticide-treated nets, repellents), dengue vaccine (CYD-TDV/Dengvaxia — only for seropositive individuals due to ADE risk in seronegative recipients; TAK-003/Qdenga — broader use profile, check local guidelines).

Clinical toolsCalculators

BMI GCS EDD Parkland Formula

Corrected Sodium Corrected Calcium Anion Gap Creatinine Clearance Insulin Calculations qSOFA Wells PE Wells DVT CHA₂DS₂-VASc HAS-BLED CURB-65 Centor/McIsaac

Brucellosis

Also known as: Undulant fever, Malta fever

Brucellosis is a zoonotic bacterial infection caused by Brucella species, acquired through direct contact with infected animals or their tissues (particularly relevant to farmers, veterinarians, and abattoir workers) or through consumption of unpasteurized dairy products, the latter representing the dominant route of acquisition in many endemic regions and an important public health target for prevention.

The organism is an intracellular pathogen, surviving and replicating within host macrophages, which contributes to both its capacity to cause chronic, relapsing disease and the specific antibiotic regimens (favoring agents with good intracellular penetration) required for effective treatment.

Presentation is often non-specific, contributing to frequent diagnostic delay, and the illness can be acute or, particularly if inadequately treated, become chronic and relapsing.

Fever, classically described as undulant (rising and falling in a wave like pattern over weeks), though this classic pattern is not always clearly seen in practice, alongside night sweats, malaise, and significant fatigue.
Arthralgia and myalgia are common, with sacroiliitis and peripheral large joint arthritis being recognized, relatively distinctive musculoskeletal manifestations.
Hepatosplenomegaly and lymphadenopathy are frequently found on examination.
Focal complications, while less common than the systemic illness, are important to recognize given their specific management implications: spondylitis (particularly lumbar, causing back pain and, if missed, potential neurological complication), epididymo-orchitis, and, rarely, endocarditis (typically affecting the aortic valve, and, though uncommon, an important cause of the small proportion of brucellosis related mortality) and neurobrucellosis (meningitis or other central nervous system involvement).

Blood culture can be diagnostic, though the organism is slow growing and the laboratory should be specifically alerted to the clinical suspicion, since standard culture protocols and durations may need extension to reliably detect it, and there is also a recognized laboratory exposure risk requiring appropriate precautions.
Serology (standard agglutination test and related assays) is widely used and often more practically useful than culture in many settings, with a significantly elevated or rising titre supporting the diagnosis, interpreted alongside the clinical picture and local epidemiological context, given that low level titres can also reflect past exposure without current active disease in endemic populations.
PCR based testing offers an alternative diagnostic approach where available, with good sensitivity and the advantage of a more rapid turnaround than culture.
FBC often shows relatively non-specific findings, sometimes with mild cytopenias reflecting reticuloendothelial and marrow involvement, and inflammatory markers are frequently elevated, though neither is specific.
Further imaging or targeted investigation is directed by the presence of any suspected focal complication, for example spinal MRI for suspected spondylitis, or echocardiography where endocarditis is a concern.

Differentials include other causes of prolonged fever with hepatosplenomegaly, including tuberculosis, typhoid fever, and visceral leishmaniasis, alongside other causes of undulant or relapsing fever patterns.

Combination antibiotic therapy is essential, given both the intracellular nature of the organism (favoring agents with good intracellular penetration) and a well recognized high relapse rate with monotherapy.
A commonly used regimen combines doxycycline with rifampicin, or doxycycline with an aminoglycoside (such as streptomycin or gentamicin), typically for a minimum of six weeks, given the organism's capacity for prolonged intracellular persistence and the associated relapse risk with shorter courses.
Focal complications generally require a longer treatment duration and, in some cases (spondylitis, endocarditis), additional specific management, including surgical input for endocarditis given the generally poor response of intracardiac brucella infection to antibiotics alone.
Prevention centers on avoiding unpasteurized dairy products in endemic areas, appropriate personal protective equipment for those with occupational animal exposure, and broader veterinary public health measures including livestock vaccination and testing programs in endemic regions.

Referral: infectious disease input for confirmed or strongly suspected cases, particularly where treatment failure, relapse, or a focal complication (spondylitis, endocarditis, neurobrucellosis) is suspected, given the specific and prolonged management these require.

Dengue Fever

Overview

Clinical Features

Diagnosis

Management

Overview

Clinical Features

Diagnosis

Management