Clinical Features of Dengue, Schistosomiasis, Leptospirosis, and Scrub Typhus
These four tropical infections share overlapping febrile presentations but can be distinguished by specific clinical patterns, timing, and associated features that guide diagnosis and treatment.
Dengue Fever
Clinical Presentation
- Presents with fever, headache, retro-orbital pain, myalgia, arthralgia, and rash with an incubation period of 4-8 days 1
- Fever typically lasts 5-7 days with a biphasic pattern in some cases 2
- Warning signs indicating progression to severe disease include persistent vomiting, severe abdominal pain, lethargy, restlessness, mucosal bleeding, and rising hematocrit with falling platelet count 1, 3
Laboratory Findings
- Thrombocytopenia is characteristic; absence significantly reduces probability of dengue 1
- Rising hematocrit (>20% increase from baseline) indicates plasma leakage 1
- Liver transaminases may be elevated but pattern is non-specific 2
Diagnostic Approach
- PCR/NAAT on serum for symptoms present 1-7 days 1
- IgM capture ELISA for symptoms >5-7 days 1
- NS1 antigen detection useful days 1-10 after symptom onset 3
Treatment
- Acetaminophen only for pain and fever; never use aspirin or NSAIDs due to bleeding risk 1, 4
- Aggressive oral hydration (>2500ml daily) for outpatient management 1
- For dengue shock syndrome: 20 mL/kg isotonic crystalloid bolus over 5-10 minutes with immediate reassessment 1, 4
Schistosomiasis (Acute Katayama Syndrome)
Clinical Presentation
- Acute schistosomiasis occurs 4-8 weeks after freshwater exposure 2
- Presents with fever, urticaria, eosinophilia, hepatosplenomegaly, and systemic symptoms 2
- Patients may not recall specific water exposure 2
- Chronic manifestations include abdominal pain, diarrhea, weight loss, and hepatosplenic disease with portal hypertension 2
Laboratory Findings
- Marked eosinophilia is characteristic during acute phase 2
- Serology becomes positive at 4-8 weeks but may be later 2
- Stool microscopy has low sensitivity; may require multiple concentrated samples 2
Diagnostic Approach
- Serology is primary diagnostic tool (>92% sensitive at presentation) 2
- Abdominal ultrasound for hepatosplenic involvement 2
- Colonoscopy with biopsy may provide histological diagnosis 2
Treatment
- Praziquantel 40 mg/kg as single dose for S. mansoni, S. intercalatum, and S. guineensis 2
- Praziquantel 60 mg/kg in two divided doses for S. japonicum and S. mekongi 2
- Consider steroids for severe acute schistosomiasis 2
Leptospirosis
Clinical Presentation
- Incubation period typically <5 days 2
- Biphasic illness: initial septicemic phase followed by immune phase 2
- Classic triad: fever, jaundice, and renal dysfunction (Weil's disease in severe cases) 2
- Conjunctival suffusion is characteristic when present 2
- Exposure history includes freshwater contact, flooding, or occupational risk 2
Laboratory Findings
- Elevated liver transaminases with conjugated hyperbilirubinemia 2
- Thrombocytopenia and leukocytosis common 2
- Renal dysfunction with elevated creatinine 2
- Creatine kinase may be markedly elevated 2
Diagnostic Approach
- Blood and CSF cultures <5 days from symptom onset (transfer at room temperature to reference lab) 2
- Serology becomes positive after first week 2
- PCR available in specialized laboratories 2
Treatment
- Doxycycline or penicillin initiated on clinical suspicion 2
- Treatment may not be helpful after jaundice has developed 2
- Severe cases require supportive care with fluid management and renal replacement therapy if needed 2
Scrub Typhus
Clinical Presentation
- Incubation period 5-7 days (up to 10 days) 2
- Sudden onset fever with chills, headache, myalgia, sweating, and vomiting 5
- Eschar (inoculation site) present in approximately 50% of cases, typically in axilla, groin, or inguinal region—this is pathognomonic when present 2, 5
- Rash develops in many patients 2
- Exposure to mites in rural areas of South Asia, Southeast Asia, and western Pacific 2
Laboratory Findings
- Elevated liver transaminases 5
- Thrombocytopenia and leukocytosis 5
- Non-specific findings that overlap with dengue, leptospirosis, and malaria 5, 6
Diagnostic Approach
- Indirect immunofluorescence assay (IFA) for IgM antibodies is reference standard 5, 6
- IgM ELISA is practical alternative with good sensitivity and specificity 5, 6
- Paired sera with ≥4-fold rise in titer confirms diagnosis 5
- Weil-Felix test has poor sensitivity and specificity; not recommended despite widespread use 6, 7
Treatment
- Doxycycline is first-line treatment; patients show dramatic response within 24-48 hours 2, 5, 8
- Alternative agents include fluoroquinolones or azithromycin 2
- Chloramphenicol or macrolides are alternatives 5
- Mortality in severe cases with multi-organ failure may reach 24% 5
Key Distinguishing Features
Timing and Exposure
- Dengue: 4-8 days post-mosquito bite (day-biting Aedes) 1
- Schistosomiasis: 4-8 weeks post-freshwater exposure 2
- Leptospirosis: <5 days post-freshwater/flooding exposure 2
- Scrub typhus: 5-7 days post-mite bite in rural areas 2
Pathognomonic Features
- Dengue: Retro-orbital pain, warning signs of plasma leakage, thrombocytopenia with rising hematocrit 1, 3
- Schistosomiasis: Marked eosinophilia 4-8 weeks after exposure 2
- Leptospirosis: Jaundice with renal dysfunction, conjunctival suffusion 2
- Scrub typhus: Eschar at bite site (when present), dramatic response to doxycycline within 24-48 hours 2, 5
Common Pitfalls
- All four conditions can present with non-specific fever, making clinical suspicion based on exposure history critical 2, 5, 6
- Coinfections are possible, particularly leptospirosis with scrub typhus, requiring consideration when fever persists despite appropriate treatment 8
- Weil-Felix test for scrub typhus should be abandoned due to poor performance 6, 7
- Dengue requires avoidance of NSAIDs/aspirin; this precaution should extend to any undifferentiated tropical fever until dengue is excluded 1, 4